Wood-Plastic Composites || Flammability and Fire Rating of Wood–Plastic Composites

461

14FLAMMABILITY AND FIRE RATING OF WOOD–PLASTIC COMPOSITES

INTRODUCTION

Acceptance criteria for deck boards and components of railing systems (ICC-ES’ AC 174, effective July 2006) are based on ASTM D 7032 and specify the fl ame spread rating to be not greater than 200 when tested in accordance with ASTM E 84.

This chapter explains the meaning of the above statements. It describes fl amma-bility and smoke/toxic gases evolution at burning of wood compared to wood– plastic composite (WPC) materials and products of different compositions and profi les. It also explains fl ammability and fi re ratings and indexes as quantitative measures for fi re hazard and fi re safety, and fi re performance characteristics in general of wood and composites.

The building codes or fi re codes regarding material requirements are based on three basic characteristics of materials: combustibility, fl ame spread, and fi re en-durance. Wood and most thermoplastic-based composites are combustible materi-als. For regulatory purposes, materials are classifi ed according to their fl ame spread index (FSI). As it will be described in more detail below in the section “ASTM recommendations,” for determining of fl ame spread index, materials are tested ac-cording to ASTM E 84 in a form of a 24-ft long and 20-in. wide assembled panel. This panel completes the top of the 25-ft long tunnel furnace. Hence, ASTM E 84 test is often called “the 25-ft tunnel test.” The panel is ignited at one end and burned under specifi ed forced draft conditions. The fl ame front position spread along the panel is recorded as a function of time. An FSI is calculated from these data using

Wood-Plastic Composites, by Anatole A. KlyosovCopyright © 2007 John Wiley & Sons, Inc.

462 FLAMMABILITY AND FIRE RATING OF WOOD–PLASTIC COMPOSITES

a prescribed formula. In other words, a FSI is a measure of the overall rate of fl ame spreading in the direction of a specifi ed airfl ow. As set points, FSI for inorganic rein-forced cement board surface is set as 0, and for select grade oak surface is arbitrarily established as 100 under the specifi ed conditions (ASTM E 84, Section 9.2).

There are four basic categories, or classes, for FSI: Class A, with FSI between 0 and 25; Class B, with FSI between 26 and 75; Class C, with FSI between 76 and 200; and below Class C, with FSI above 200 (unclassifi ed materials). Classes A, B, and C sometimes are called Classes I, II, and III.

In the same “25-ft tunnel test” the so-called smoke development index (SDI) can also be determined. The smoke measurement is based on the percentage of retarda-tion of light passing through the tunnel exhaust stream and detected by a photocell, and then data obtained are converted to the SDI, with red oak fl ooring set at 100. AC 174 does not specify any particular SDI as the code requirement, but the industry generally considers SDI above 450 as hazardous and not acceptable, particularly for interior fi nish.

These are introductory data necessary for the following considerations, and they will be discussed in more detail later in this chapter.

FLAMMABILITY OF WOOD

The FSI for ordinary wood species is typically between 100 and 200, for some spe-cial cases it is as low as 60–70 (Table 14.1) To burn, wood should be exposed to heat

TABLE 14.1 ASTM E 84 fl ame spread indexes for 19-mm-thick solid lumber [1]

Species Flame spread index Smoke developed index

Yellow poplar 170–185 —Southern pine 130–195 —Ponderosa pine 105–230 (Average 154) —Eastern white pine 120–215 122Cypress 145–150 —Red pine 142 229Sweetgum 140–155 —Walnut 130–140 —Cottonwood 115 —Birch 105–110 —Maple 104 —Oak (red, white) 100 100Spruce, Sitka 74–100 74Douglas-fi r 70–100 —Yellow-cedar 78 90Redwood 70 —Fir, Pacifi c silver 69 58Spruce, eastern 65 —

an air/oxygen. Burning occurs in stages: thermal decomposition with evolution of volatiles and heat release, ignition of fl ammable volatiles, combustion as fl ames, fl ame spread with evolution of smoke and toxic gases, and charring. Each stage can proceed differently depending on wood density, morphology, and composition (amount of lignin, etc.), the rate of heating, the temperatures, the moisture content, and the extent of air ventilation.

Generally, the same stages take place in burning of WPCs. However, composites provide much more variations in their chemical composition, density, the nature of plastics, plastic content, amount of fi llers, and so on.

IGNITION OF COMPOSITE MATERIALS

Composite materials, as well as plastics, do not ignite, per se. Ignition happens when the fl ammable material reaches a certain temperature in atmosphere that contains suffi cient amount of oxygen. Ignition can be piloted, that is, in the presence of a fl ame (or another ignition source), or unpiloted, such as in a furnace with tempera-ture at or above the ignition point.

If to place a piece (or pellets, sheet, fi lm, etc.) of HDPE into an oven at ambient temperature, close the oven door, program temperature at a rather high level (say, 600�C), and let it rise, at some point one can hear a pop inside the oven. Opening the door would reveal the sample in fl ames. To get ignited, the sample went through stages, such as melting the plastic, partial thermal decomposition resulting in evolu-tion of volatiles, including fl ammable ones, and at some temperature the point of ignition of those volatiles and the sample itself will be reached. For polyethylene this temperature is about 360–367�C (680–693�F) [2], depending on a size of the sample.

Ignition point of fi lled HDPE, or HDPE-based composites, would be about the same provided that the material does not contain active fl ame retardants. Indeed, fi lled or not fi lled, HDPE in the material would still melt and emit fl ammable VOC (volatile organic compounds), which would ignite at a certain temperature point, close to that one for neat HDPE. A difference would depend mainly on the amount of HDPE in the material and the size of the sample.

For example, at the same conditions and for 3-g samples of HDPE and GeoDeck, ignition temperature was 806 and 815�F (435�C), respectively. Experiments with GeoDeck have shown that at 430�C ignition did not occur for more than 10 min; at 435�C the specimen ignited at 6:30 min, at 440�C it ignited at 5:45 min, and at 450�C the ignition occured at 4:00 min.

HDPE fi lled with a fl ame-retardant ATH (aluminum trihydrate) showed the igni-tion temperature of 445�C (833�F). The 10�C delay was caused by ATH, which re-leases water vapor at about 180–240�C (360–460�F), which that in turn cools down the material.

HDPE-based WPC materials all have rather similar ignition points. When tested at the same conditions, they showed almost the same self-ignition temperatures (SIT):

IGNITION OF COMPOSITE MATERIALS 463


TimberTech 405�C,Trex and TekDek 410�C,GeoDeck 435�C.

GeoDeck has shown a slightly higher ignition point because it contains the high-est amounts of inorganic fi llers, more than 20%. In these conditions, pressure-treated lumber showed SIT at 430–435�C (806–815�C).

A sample surface is ignited by the fl ow of energy, or heat fl ux, from a heat source. Table 14.2 shows some values of heat fl ux and the respective ignition time for several wood species.

One can see how much the increase of the imposed heat fl ux decreases time to ignition, and how much the density of the materials affects ignition time. The lower the density of materials, the lower the ignition surface temperature. Moisture content in the material is also very important.

When the material contains some fl ame retardants, for example, ATH, its igni-tion point often shifts up. ATH, as it will be explained below in more detail, releases water at a certain temperature level. Water cools down the material and increases an apparent ignition time; it also reduces the heat produced by the burning material and therefore quenches fl ames.

Table 14.3 shows data on ignition temperatures of commercial WPCs, reported by the manufacturers.

FLAME SPREAD INDEXES AND FIRE RATING OF COMPOSITE MATERIALS

Essentially, FSI indicates how rapidly the fuel, emanating from the burning mate-rial, travels along the testing panel and reaches the ignition temperature under the heating by the fl ame front and the controlled heating, and the controlled air draft. The FSI greatly depends on the material’s thermal conductivity, heat capacitance, thickness of the panel, shape (solid or hollow), amount of inorganic fi llers (if any), fl ame- retardants (if any), and so on.

Some plastic lumber or WPC deck boards are not suitable to test according to ASTM E 84. As the fi re exposure in the ASTM test is on the underside of a horizontal

TABLE 14.2 Flammability data for selected wood species [3]

SpeciesDensity (g/cm3)

Ignition time (s) for heat fl ux

18 (kW/m2) 55 (kW/m2)

Red oak 0.66 930 13Southern pine 0.51 740 5Redwood 0.31 741 3Basswood 0.31 183 5

Data are determined using ASTM E 906.

testing panel, when the material melts and drips or is not self-supporting, the test is commonly terminated.

There are three fi re ratings on fl ame spread, based on the numerical indexes calculated from test data, according to ASTM E 84:

Class A: Flame spread index 0–25

Class B: Flame spread index 26–75

Class C: Flame spread index 76–200

FSIs for commercial WPC materials and products published by manufacturers (in ICC–ES reports and elsewhere) are given in Table 14.4.

Table 14.5 shows available data on burning rate of some composite materials determined according to ASTM D 635.

TABLE 14.3 Ignition temperatures (FIT or SIT) for plastic-based commercial composite deck boards, reported by manufacturers and determined according to ASTM D 1929

Deck board ManufacturerPrincipal

ingredients FIT or SIT

Ignition temperature, �C

(�F)

EverX Universal Forest Products

HDPE 50%, wood fl our 50%

SIT 436 (817)FIT 355 (671)

USPL U.S. Plastic Lumber HDPE, wood fl our SIT 387 (729)FIT 381 (718)

E-Z Deck Pultronex Corporation Polyester, glass fi ber

FIT, SIT

�343 (� 650)

Ecoboard (nonreinforced)

Trelleborg Engineered Products, Inc.

100% polyethylene FIT 350 (660)

Ecoboard (reinforced)

HDPE 70%, LDPE 10%, fi berglass 20%

FIT 350 (660)

Trex Trex Company Polyethylene 50%, wood fl our 50%

SIT 395 (743)FIT 370 (698)

GeoDeck LDI Composites HDPE 40%, rice hulls 28%, Biodac 28%

SIT 435 (815)

Nexwood Nexwood Industries 40% HDPE, 60% rice hulls

SIT 450 (842)

ChoiceDek Advanced Environmental Recycling Technologies

50% HDPE, 50% wood fi ber

SIT 394 (741)FIT 387 (729)

Boardwalk CertainTeed Corporation

PVC, wood fl our SIT 345 (653)FIT 361 (682)

FLAME SPREAD INDEXES AND FIRE RATING OF COMPOSITE MATERIALS 465


TABLE 14.4 Flame spread indexes for commercial WPCs determined according to ASTM E 84

Deck boards (solid or hollow) Profi le Manufacturer

Principal ingredients

Flame spread index

USPL Solid U.S. Plastic Lumber HDPE, wood fl our

76

Millenium Hollow Millenium Decking PVC, wood fl our 60Nexwood Hollow Nexwood Industries HDPE, rice hulls 65Life Long Solid,

channeled and hollow

Brite Manufacturing

Polyethylene, wood fl our

�200

GeoDeck Hollow LDI Composites HDPE, rice hull, Biodac

100 ± 3

Trex Solid Trex Company Polyethylene, wood fl our

80, between 75 and 200,120a

Monarch Solid Green Tree Composites

HDPE, wood fl our (saw dust)

130

Boardwalk Solid CertainTeed Corporation

PVC, wood fl our 25

Epoch (Evergrain)

Solid Epoch Composite Products

Polyethylene, wood fl our (compression molding)

Between 76 and 200

Rhino Deck Solid Master Mark Plastic Products

Thermoplastic, wood fi ber

169

Timber Tech Hollow TimberTech HDPE, wood fi bers

75

EverX Hollow Universal Forest Products Ventures II

HDPE, wood fi ber

46

WeatherBest Solid Louisiana-Pacifi c Corporation

HDPE, wood fl our, 12% talc � phenol-formaldehyde resin

�200

E-Z Deck Solid Pultronex Corporation

Polyester, glass fi ber

80

Presidio Hollow Westech Building Products, Inc.

100% PVC No more than 75

XTENDEX Hollow Carney Timber Company

HDPE, rice husks 104

ChoiceDek Channeled Advanced Environmental Recycling Technologies, Inc.

HDPE, wood fi ber

100

For a comparison, some other neat or fi lled plastics are shown.a CAN/ULC-S102.2-M88

EFFECT OF MINERAL FILLERS ON FLAMMABILITY

Many inert fi llers, such as calcium carbonate, talc, clay, cellulose fi ber, glass fi ber, and so on, can slow down fl ame spread—by just “removing food” for fl ame propa-gation, or slow heat generation, favor charring, and so on—but they do not signifi -cantly change the ignition point. They do not act as “active” fl ame retardants, which typically produce some counter-fl ame or counter-ignition matters, such as water or infl ammable gases. They act rather by diluting the fuel in the solid (plastic) phase. Calcium carbonate evolves inert gases (carbon dioxide) at about 900�C, which is too high in order to serve as a fl ame retardant.

For example, when ASTM D 635 procedure was used, a “basic” composite ma-terial (42% HDPE, 57% rice hulls, and 1% lubricant) burnt for 3�48�. For a com-parison, a neat HDPE sample burnt for 3�30� ( ± 12�). With 10% fl y ash added to the “basic” composition, the resulting composite burnt for 4�05�. With 25% fl y ash, for 4�42�. With 40% fl y ash, for 8�09� (in some experiments, fl ame self-extinguished after about 5 min).

When compared with active fl ame retardants, such as decabrom (see below), the addition of 10% decabrom resulted in a delay of burning time of the sample to 5�50�, with 15, 20, or 30% decabrom the samples did not burn at all. The sample with 10% decabrom and 2.5% antimony oxide did not burn as well. Understandably, the sample with 12% decabrom and 3.5% antimony oxide did not burn too.

SMOKE AND TOXIC GASES, AND SMOKE DEVELOPMENT INDEX

Smoke and toxic gases associated with fi re represent one of the most important problems, particularly when plastic-containing materials are burning. Smoke contains gases, solid particles, droplets of liquids, including water and molten plastic. Smoke is harmful to health, obscures vision, causes choking and sometimes death. This ex-plains a general concern, which general public expresses regarding halogen- containing fl ame retardants, even when tests consistently show that some of them are harmless.

TABLE 14.5 Burning rate of WPCs according to ASTM D 635

Composite material Burning rate (in./min)

Trex 0.71a

Rhino Deck 0.69–0.86b

Nexwood 0.68GeoDeck 0.29c

E-Z Deck 0.28

aAs an example: burning time 248 ± 13 s, burning distance 75 mm, burning rate 18.1 ± 1.0 mm/min, or 0.71 in/min.bDensity of smoke (ASTM D 2843-93) 5.5% per UBC 26-5.cAs an example: burning time 609 ± 112 s, burning distance 75 mm, burning rate 7.4 ± 1.4 mm/min, or 0.29 in./min.

SMOKE AND TOXIC GASES, AND SMOKE DEVELOPMENT INDEX 467


Generally, but not necessarily, the higher the FSI, the higher the smoke developed index (SDI) (see Table 14.1). For wood the SDI is typically between 60 and 230. WPCs also often exceed these values (see Table 14.6).

Virgin (rigid) poly(vinyl chloride) contains about 57% chlorine and shows low fl ammability. PVC-based WPCs have FSI between 25 and 60. When burns, PVC pyrolyzes to form HCl and volatile organic (aromatic) compounds, which evolve large amounts of smoke.

FLAME RETARDANTS FOR PLASTICS AND COMPOSITE MATERIALS

Flame retardants for plastics and WPCs are completely different from those of wood materials. Wood is typically impregnated with solutions of fl ame retardants, com-monly salts, such as monoammonium and diammonium phosphate, ammonium sulfate, zinc chloride, sodium tetraborate, boric acid, and guanylurea phosphate. In

TABLE 14.6 Smoke developed indexes for commercial WPCs, determined according to ASTM E 84

Deck boards(solid or hollow) Profi le Manufacturer

Principal ingredients

Smoke development index

GeoDeck Hollow LDI Composites HDPE, rice hull, Biodac

166 ± 7

Rhino Deck Solid Master Mark Plastics

245

Nexwood Hollow Nexwood Industries

HDPE, rice hulls 340

ChoiceDek Channeled Advanced Environmental Recycling Technologies, Inc.

HDPE, wood fi ber 360

Millenium Hollow Millenium Decking

PVC, wood fl our 440

Timber Tech Hollow Timbertech Ltd. HDPE, minerals, wood fi ber

�450

Boardwalk Solid CertainTeed PVC, wood fl our �450Epoch

(Evergrain)Solid Epoch Composite

ProductsPolyethylene, wood

fl our (compression molding)

�450

Trex Solid Trex Company Polyethylene, wood fl our

285�450�500a

XTENDEX Hollow Carney Timber Company

HDPE, rice husks 1597

a CAN/ULC-S102.2-M88.

plastics and WPCs, however, fl ame retardants are added as solids directly into the formulation. Hence, fl ame retardants for plastics and WPCs should be temperature-resistant, in order not to be decomposed during processing.

PVC-based composites, unlike many other thermoplastic-based composites, are “natural” fi re-resistant materials (see Chapter 2). Their FSI is in the range of 25–60 (Table 14.4), in Class A–B range. However, PVC also often employs fl ame retar-dants, mainly ATH, for further decrease in its fl ammability.

Generally, all groups of plastics utilize fl ame retardants when needed for their performance and specifi c application. Below is a short chart showing fl ame retar-dants that are used the most in the respective plastics.

• PE and PP ATH (almost ten times more than the second FR, chlorinated compounds)

• PVC ATH (twice as much as compared with the second FR, organophosphorus compounds, nonhalogenated)

• ABS Brominated compounds and antimony oxides

Consumption of magnesium hydroxide compared to ATH as fl ame retardants is lower 15–20 times by volume and about 10 times lower by a dollar value [4].

Very few, if any, of commercial WPCs employ added fl ame retardants to be-come Class A or Class B deck boards. A rather common belief was that it does not make much sense: What is good in a fi reproof deck if the house is burnt but the deck stays? However, because of massive brush fi res, particularly in Southern California, Arizona, Colorado, New Mexico, and Oregon, a number of legislations are considering state laws requiring fi re-resistant decks. For example, the state of California recently approved a new construction building code for new construc-tion that calls for improved fi re resistance from many building products including WPC decking. The new legislation will be effective starting January 2008 [5]. If the California regulations are adopted by some other states, Classes A and B WPC decks, containing effective fl ame retardants, might soon become a commodity in the market.

Alternatively (or, rather, along with) the opportunity for PVC-based products will be boosted.

Flame retardants for plastic and WPCs can be subdivided into the following principal groups according to their physical action:

• Water-releasing and cooling, creating a “heat sink”;

• Halogen (gas) forming and fl ame poisoning, or fl ame choking;

• Char forming, formation of a protective layer.

As it was indicated above, many inert fi llers, such as calcium carbonate, talc, clay, glass fi ber, and so on, serve as “passive” fl ame retardants, by just “removing food” for fl ame propagation, or slow heat generation, favor charring, and so on, but they do not signifi cantly change the ignition point.

FLAME RETARDANTS FOR PLASTICS AND COMPOSITE MATERIALS 469


Zinc borates, such as 4ZnO � B2O3 � H2O, 2ZnO � 3B2O3 � 3.5H2O, were shown to act as synergists with ATH and Mg(OH)2 as fl ame retardants and smoke suppressants [6]. Their pyrolysis leads to a formation of a protective vitreous barrier, as low melting glasses can do. An example of zinc borate as a commer-cial fl ame retardant, recommended for plastics, is Firebrake® ZB by Borax (U.S. Borax Inc., Valencia, CA). This material releases its bound water at tempera-tures exceeding 290�C (554�F). At this temperature, ATH already releases about 10% of its water, if temperature increases by 10�C/min (see below). Firebrake® is claimed by its manufacturer to be fl ame retardant at 3–25% in halogen-con-taining plastics, or at higher levels with halogen-free plastics. It is typically used along with ATH or magnesium hydroxide. Median particle size of three main brands of Firebrake® are as follows: Firebrake® ZB, 7–9 µm, Firebrake® ZB-Fine, 3 µm, and Firebrake® ZB-XF, 2 µm (top particle size 12 µm). As Firebrake® has a low water solubility (less than 0.28%), it washes out only a little from composite materials used outdoors.

The way that fl ame retardants work is better understood considering the way how materials burn. As temperature of solid materials increases above certain value, they decompose via pyrolysis and release fl ammable gases. These gases burn with oxygen in the air, and the fl ame propagates, or spreads. Organic molecules decompose via free radicals to give free carbon that can react with oxygen to give CO and CO2.

Active fl ame retardants inhibit or suppress combustion by several mechanisms, as briefl y mentioned above:

• By releasing water (ATH, i.e., alumina trihydrate, Al(OH)3; magnesium hy-droxide Mg(OH)2) that acts as heat sinks and prevents oxygen to get to fl am-mable compounds, or by forming of a protective layer and by dilution and coating. ATH alone accounts for about 20% of all fl ame retardants used in plastics.

• By forming nonfl ammable gases to poison fl ame, to shield fl ammable materials from oxygen, insulating them, as halogenated fl ame retardants do. Brominated fl ame retardants remove free radicals in the gas phase and as a result prevent or slow down the burning process by reducing heat generation and by producing fl ammable gases. Brominated fl ame retardants account for about 32% of fl ame retardants, plus 6% goes for chlorinated fl ame retardants. Halogenated fl ame retardants are subdivided into halogenated organic and halogenated organo-phosphate esters.

• By acting as char formers, as phosphorous fl ame retardants do. They are also subdivided into nonhalogenated organophosphate esters, ammonium polyphos-phate, and others. When heated, they produce a solid form of phosphoric acid that in turn chars the material and shields it from releasing of fl ammable gases feeding fl ames. Phosphorous fl ame retardants account for about 20% of fl ame retardants in the industry (mainly not with polyolefi ns). Boron compounds also work as char formers [2].

Some of the inorganic compounds, such as antimony trioxide (Sb2O3), or boron-based compounds, such as zinc borate, function as synergists rather than directly as fl ame retardants but enhance the effectiveness of the latter. Antimony trioxide is used mainly with halogenated fl ame retardants.

Flame Retardants in Plastics

Flame retardants are used very little in WPC materials compared to large scale ap-plication in plastics, such as in electrical applications (TBBA in epoxy laminated printed circuit boards, existing there as brominated epoxy polymers, or BEOs) or carpets. In epoxy resins it is a reactive chemical, existing as part of the polymer chain, TBBPA (tetrabromobisphenol-A) [7]. Another example—polybromostyrene fl ame retardants for use in Nylon 6 and Nylon 66 applications for connectors and high-temperature polyamide applications (PDBS 80, BrPS, BrPS-1, Firemaster® PBS-64HW, and Firemaster® CP-44HF, the latter is a copolymer of di- and tri-bro-mostyrene with glycidyl methacrylate).

Flame retardants that are often used in polycarbonate/ABS plastics (such as in computer industry) include nonhalogen triaryl phosphates, such as RDP [resorcinol bis (diphenyl phosphate)] and BDP [bisphenol A bis(diphenyl phosphate)]. As BDP has lower phosphorus content compared to that of RDP, more of it should be used to match the fl ammability performance of RDP. In one particular study using polycar-bonate–ABS alloy, 9% of RDP or 12.3% of BDP was employed and showed equal to each other and excellent fl ame retardant properties [8].

Restrictions or Prohibitions of Some Brominated Flame Retardants

Use of some of the fl ame retardants, particularly brominated ones (PBDEs, or poly-brominated diphenyl esters), was prohibited by European Union Risk Assessment program. Among them were pentabromodiphenyl ether (pentaBDE), which was used primarily in polyurethane foam, and octabromodiphenyl ether (octaBDE), used mainly in electrical and electronic equipment and automobiles (both were prohibited by EU in August, 2004). In the United States, production of pentaBDE was ceased in 2004 and its manufacture and import into the United States is prohibited. Octa-BDE was scheduled to be prohibited in 2006 in a number of states in the United States [9]. Both pentaBDE and octaBDE are linked to fetal development and thyroid prob-lems; however, the concentrations of PBDEs in human blood serum and breast milk have been doubling every 2–5 years, according to the Centers for Disease Control & Prevention (CDC).

Decabromodiphenyl ether (decaBDE) was recognized as safe, with “no need for risk reduction measures” both in the United States and Europe [9], though CDC lists it as a possible human carcinogen. Currently, under the investigation by EU are the following fl ame retardants: TBBPA (tetrabromobisphenol-A), HBCD (hexabro-mocyclododecane), TCEP [tris(2-chloroethyl)ethyl)phosphate], TCPP [tris(2-chloropropyl)phosphate], TDCP [tris(2-chloro-1-(chloromethyl)ethyl) phosphate],



and V-6 [2,2-bis(chloromethyl)trimethylene bis (bis(2-chloroethyl)phosphate)]. The main application for TCEP, TCPP, TDCP, and V-6 is polyurethane foam.

It looks like, however, that the “safe status” of decaBDE might be soon reconsid-ered. Recent researches have shown that microorganisms present in North American and European soil break down relatively stable decaBDE into octaBDE and then pentaBDE, both toxic. These microorganisms were identifi ed as Sulfurospirillum and Dehalococcoides [10].

Chlorine-Containing Flame Retardants

Chlorine-containing fl ame retardants can be divided into three groups: aliphatic, alicyclic (cycloaliphatic), and aromatic. Their thermostability is increased in this order, but fl ame retardant effi ciency is decreased in the same order. This reciprocal tendency is common among fl ame retardants. Clearly, the higher the thermal stabil-ity, the higher the temperature at which the fl ame retardant becomes chemically active and functional as a fl ame retardant.

A common disadvantage of chlorine-containing fl ame retardants is that they have to be added in quantities, which in turn decrease mechanical properties of the polymer materials. The same situation in terms of large amount that should be added into the base material holds for mineral fl ame retardants as well (ATH, Mg(OH)2); however, minerals typically improve both fl exural modulus (stiffness) and fl exural strength of composites.

Aliphatic chlorine fl ame retardants are represented by chloroparaffi ns, with chlo-rine content between 40 and 70%. They typically have a poor thermal resistance, as their dechlorination often starts at 180�C (356�F); hence, their application is re-stricted by polyethylenes and PVC.

Dover Chemical Corporation produces resinous chlorinated paraffi ns under a name Chlorez® and advocates their usage as fl ame-retardant additives in plastics. All Chlorez® grades have a physical form of white powder (particles smaller than 50 mesh) with chlorine content around 70%. Chlorez® is not recommended to be processed above 180�C (356�F). Indeed, an attempt to compound one of these materials with a WPC at 190�C (374�F) has resulted in a rather violent decomposition of the material. The melt turned dark, and some foaming occurred with an accompanying strong smell.

On the contrary, chloroaromatic compounds, such as decachlorodiphenyl, are too stable thermally to be widely used as fl ame retardants.

An example of a successful application of Chlorez® in making of an HDPE-based WPC at 325�F (die lip at 340�F) was provided by Dover Chemical Corporation (Thomas Kelley). The base WPC formulation was 40-mesh pine fl our (52–55% w/w), and MFI of HDPE was 0.4. A profi le was extruded using a 35-mm conical twin-screw extruder from Cincinnati Milacron at WMEL, Washington State University Chlorez® was employed at 10–15% w/w along with 2.5–5% of Sb2O3 (antimony trioxide, or ATO) as a synergist. For comparison, Decabrom (10% w/w) along with 3% of Sb2O3 was also evaluated. According to the company data, the composite deck boards loaded both Chlorez®/ATO and Decabrom/ATO had a regular shape; however, Chlorez®-loaded boards showed better fi re-resistant properties compared to Decabrom-loaded boards.

An example of cycloaliphatic chlorine fl ame retardants is hexachlorocyclo-pentadiene (Dechlorane Plus®, or CFR). It is typically used in polyester resins in which hexachlorocyclopentadiene is converted into functional derivatives by ma-leic anhydride to give the “net anhydride.” It is the most stable chlorinated fl ame retardant(CFR). CFR is commonly used in synergism with antimony oxide, zinc borate, zinc oxide, and iron oxides. In Nylon 66, CFR is often used in concentrations of 8–25%, along with 1–10% of Sb2O3, zinc borate, or iron oxide [11].

ATH (Aluminum Trihydrate) and MDH (Magnesium Hydroxide)

A typical example of “active” fl ame retardants is represented by ATH, that is, aluminum trihydrate. When ATH is heated with a heating rate of 10�C/min, it starts releasing water at about 225�C (437�F). At 300�C, ATH releases 12% water by weight. At 334�C (633�F), the rate of water reaches its maximum, with about 28% of water release, and the process slows down, reaching 35% of water release at 900�C. Water release reduces the heat from the oxidized plastic and quenches fl ames.

2Al(OH)3 → Al2O3 + 3H2O

This is an endothermic decomposition, with ∆H 298 kJ/mol (71.2 kcal/mol).Generally, ATH is considered to be thermally stable at around 180–200�C (360–

400�F), and—with some reservations—until 216�C (420�F). Some data indicate the decomposition of ATH in the temperature range of 180–240�C (360–460�F). ATH is usually cream-colored, free-fl owing powder with specifi c gravity of 2.42 g/cm3 loose bulk density of 70 lb/ft3 (1.12 g/cm3), and the so-called packed bulk density of 55 lb/ft3 (1.36 g/cm3). A typical commercial grade of ATH (for example, product of Alcan Chemicals, Cleveland, OH), contains up to 15% of powder with mesh size of 100 and larger particles, 67–87% with mesh size 200–200, and between 1 and 12% of mesh size 325.

Magnesium hydroxide converts to magnesium oxide and water above 300–330�C (570–630�F), and according to other data in the range of 330–460�C (630–860�F), which at any rate is in a signifi cantly higher temperature range compared with that of aluminum trihydrate. Besides, this is more endothermic reaction, with a higher enthalpy of decomposition, hence, more effi cient as a “heat sink.”

Mg(OH)2 → MgO + H2O

This is also an endothermic decomposition, with ∆H 380 kJ/mol (90.8 kcal/mol).Obviously, ATH cannot be used in thermoplastics other than polyethylene and

PVC, and in the respective plastic-based composite materials. A common disadvan-tage of ATH and MDH (magnesium hydroxide) is that in order to provide a suffi cient level of fl ame retardancy, they have to be used in large amounts, such as 50–65% and not below 40%.

As it could have been expected, the decomposition of ATH to Al2O3 during the heating of the polymer resulted in an increase of the ignition time [12].



ATH Dehydration: A Quantitative Approach

Ashing of a sample of plastic (or a plastic-based composition) containing ATH can determine how much the ATH was dehydrated during the processing.

Though aluminum trihydrate, Al2O3 • 3H2O, or [Al(OH)3]2, theoretically contains three water molecule, in reality it typically contains a slightly reduced amount of wa-ter. A direct analysis of eight commercial ATH samples resulted in only 2.86 water molecules on average per Al2O3 in ATH.

This was determined as follows. Eight ATH samples were studied:

1. RIH-30, 10 mc, Riverland Ind. Inc.

2. Haltex

3. Huber, Surface modifi ed HYMODTH SL, 36SL

4. Huber, Surface modifi ed HYMODTH SP, 36SP

5. Huber SB-36

6. Huber SB-336

7. Huber MoldTM A120

8. Alcoa Inc., 10 mc.

Theoretical molecular weight of Al2O3 • 3H2O is 156.Molecular weight of Al2O3 (ash) is 102.Therefore, ash content in ATH, having 100% of bound water, is 102/156 65.38%.If a whole water molecule–on average—is lost as a result of a temperature treat-

ment of some other effects, the resulting aluminum dihydrate Al2O3 • 2H2O will pro-duce 102/138 73.91% of ash by weight. If two water molecule are lost, the result-ing aluminum monohydrate Al2O3 • H2O will produce 85.0% of ash. Obviously, if all three water molecules are lost, resulting in pure aluminum oxide Al2O3, after ashing of it all 100% of ash will be observed.

At more gentle temperature treatment, only a fraction of water—on average—can be lost. In other words, some ATH molecules will lose a water molecule, and some ATH molecules will not. Below is a brief chart showing how ash content of respective ATH samples would look like (Table 14.7).

TABLE 14.7 An amount of ash (per cent) after temperature treatment (at 525�C for 24 h) of Aluminum Trihydrate (ATH) until constant weight. Theoretical data.

Quantity of water molecules present on average per ATH molecule

Ash content (%)

3.0 65.382.9 66.152.8 66.932.7 67.732.6 68.552.5 69.39

When all eight ATH samples listed above were ashed at 525�C for 24 h (until constant weight), results looked as given in Table 14.8.

Thus, all eight ATH sample had a very close to each other amount of bound water, namely 2.86, rather than the theoretical amount of 3.0 water molecules.

The same approach can be applied to plastics, fi lled with ATH (or any other fi ller). A compounded mix of 60% ATH and 40% HDPE was prepared and a sample of the fi lled plastic was ashed. Theoretically, the amount of ash should be 39.23% by weight. This fi gure can be obtained by taking 65.38% ash content in ATH and taking 60% of it (because the ATH was diluted by 40% of HDPE). If to introduce the correction that there were only 2.86 water molecules per ATH (see above), the amount of ash should be 40.0%.

Any fi gure for a weight percentage of the ashed HDPE/ATH higher than 40.0% would indicate that the ATH in the material was partially (or completely) decom-posed compared with the initial ATH.

An actual experiment showed ash content in four HDPE (40%)—ATH (60%) samples, prepared with ATH samples 2, 3, 7 and, 8 above. Ash contents were 40.16, 40.13, 39.78, and 40.19%, respectively. These data indicate that there was practically no decomposition of ATH in the course of compounding with ATH (less than 0.1 water molecule per ATH molecule was lost). The compounding was done using the Brabender mixing head.

TABLE 14.8 Determination of water content in various commercial ATH samples from their ashing (at 525�C for 24 h) data. The manufacturers names are listed on p. 474.

ATH sample (see list above)

Ashed sample

weight (g)Ash weight

(g)Ash, % of the initial

sample weightAverage quantity of water

molecules per ATH

1 1.514 1.0111.004

66.7866.31

2.822.88

2 1.379 0.9270.920

67.2266.72

2.772.83

3 1.889 1.2541.244

66.3865.85

2.872.94

4 1.765 1.1831.175

67.0366.57

2.792.85

5 2.102 1.4061.397

66.8966.46

2.812.86

6 2.081 1.3901.382

66.7966.41

2.822.87

7 1.246 0.8380.832

67.2666.77

2.762.82

8 1.414 0.9450.940

66.8366.46

2.812.86

Average 66.67 ± 0.36 2.86 ± 0.04



When more fi llers, such as fl y ash, zinc borate, and a colorant, were added to the formulation and compounded with HDPE and ATH, ATH lost 0.6 water molecule on average, as it was shown by ashing. Repeat with the same formulation but with a gentler mixing resulted in a loss of only 0.3 water molecule per ATH molecule.

Flame Retardants with Wood–Plastic Composites

Decabrom and antimony oxide were tested as fl ame retardants with HDPE-based composite materials. Tests were conducted according to ASTM D 635 (plank size of 125 � 13 � 7 mm, 75 mm of length fl ame spreading). Decabrom in amounts of 12 to 20–30% prevented the composite from burning, with or without added antimony oxide (2.5–3.5%). 10% decabrom did not prevent burning, but in the presence of 2.5–10% of antimony oxide it made fl ame consistently die. Antimony oxide by itself in the amount of 20% did not affect noticeably the burning, as well as 3% Vitrolite.

Nanoparticles as Flame Retardants

Lately, fl ame retarding effects of nanoclay particles on fl ammability of WPCs, particularly in the presence of coupling agents, have attracted attention. Typically, conventional fl ame retardants are used at fi lling levels of 40–60% (w/w) and even higher. Nanofi llers can reportedly avoid this disadvantage of traditional fl ame retardants. Nanoparticles or nanofi llers are collective terms for modifi ed layered silicates (organoclay) or carbon nanotubes dispersed in the polymer matrix, when the particles’ size is in order of nanometers, or tens of nanometers. A plastic fi lled with nanoparticles typically in the range of 2–10% (w/w) is called a nanocomposite.

There are two basic types of nanocomposites in which particles are intercalated or exfoliated. In an intercalated composite, the nanodispersed fi ller still consists of ordered structures of smaller individual particles packed into intercalated structures. Exfoliated particles are those dispersed into practically individual units, randomly distributed in the composite. Layered silicates, such as montmorillonite clays or or-ganoclays, can be used in nanocomposites. As clays are hydrophilic and polyolefi ns are hydrophobic, it is not easy to make nanocomposite based on polyethylene or polypropylene because of their natural incompatibility.

Both intercalated and exfoliated nanocomposites, containing 3–5% of nanopar-ticles (w/w), reportedly show better or comparable fl ame resistance compared with plastics fi lled up to 30–50% with traditional fl ame retardants. Another way to increase fl ame retardancy is to combine ATH or magnesium hydroxide with organo-clays. It was reported that organoclays and some classical fl ame retardants, such as brominated compounds, showed a synergism between them [13].

In some cases only small amount of nanoparticles, such as 5% w/w, was claimed to be necessary to signifi cantly reduce fl ammability of WPC. According to Ref. [14], a clay particle of a size of 8 µm consists of about 3000 platelets, which can be exfoliated into particles of 200 nm in length and 1 nm in thickness and intercalated into packets of these platelets of the same length of 200 nm, and thickness of 30 nm.

According to the authors, burning rate (ASTM D 635) of the WPC in the presence of the nanoclay as a part of the composition decreased from the initial (no nanoclay) 29 to 13 mm/min. In another experiment, burning rate decreased from the initial 42 to 32 mm/min in the presence of 5% (w/w) of nanoclay, and from 32 to 26 mm/min in the presence of 0.5% of the nanoclay.

Generally, nanomaterials as fl ame retardants do not have commercial appli-cations. Data obtained are commonly recognized as preliminary, and they are described here just as preliminary as well. One more example of such data is a study of heat release and char formation (in per cent units) at burning of polypropylene fi lled with magnesium hydroxide (5 µm, 1 µm particles, and nanoparticles) (Table 14.9).

Thus, addition of the nanoparticles to a regular size Mg(OH)2 led to a signifi cant decrease of heat release capacity of fi lled polypropylene.

Regarding char formation, pure polypropylene showed a residual char of 0.5%. In the presence of 65% of Mg(OH)2 (regular or nano), a residual oxide or char was 51.3–54.8%, whereas an expected (theoretical) amount of char was 42.8–44.9%. The authors concluded that the formation of noncombustible carbon char from polypropylene was higher in the presence of the magnesium oxide [15].

ASTM RECOMMENDATIONS

Note 1: ASTM’s policy is not to use descriptive terms such as “nonfl ammable,” “fl ame retardant,” “self-extinguishing,” “non-burning,” and similar. According to ASTM, results of any of fi re test methods must be described in numbers, such as “fl ame spread index of 75,” or “fl ame spread index below 200,” or “a burning rate of 0.72 in./min,” or “a burning distance of 75 mm.”

Note 2: Numerical fi re test results obtained using different ASTM procedure generally cannot be comparable and/or cannot be translated to expected results of, say, method ASTM E 84, using some empirical coeffi cients. There are too many noncontrollable factors involved in small and large-scale burning.

TABLE 14.9 Heat release in Mg(OH)2 fi lled polypropylene [15]

Amount of Mg(OH)2 in polypropylene (%, w/w) Mg(OH)2 particle size

Burning heat release (J/g-K)

0 (neat PP) — 118365 5 µm 31065 1 µm 29065 Nanoparticles 26165 32.5% of 5-mc � 32.5%

of nanoparticles273

65 32.5% of 1-mc � 32.5% of nanoparticles

253

ASTM RECOMMENDATIONS 477


ASTM D 635 “Standard Test Method for Rate of Burning and/or Extent and Time of Burning of Plastics in a Horizontal Position”

The ASTM fi re test procedure describes a small-scale laboratory determination of the relative linear rate of burning of plastics and plastic-based composites. Speci-mens can be in the form of bars, molded or cut from sheets, plates, or panels and tested in the horizontal position. The results of the test are intended to serve as a preliminary indication to their fl ammability.

In summary, a bar specimen of 125 mm (5 in.) long, 13 mm (0.5-in.) wide, and about 3 mm (0.12 in.) thick (but not more than 13 mm [0.5 in.] thick) is supported horizontally at one end, and the free end is exposed to a specifi ed gas fl ame for 30 s. If the specimen burns to the 100 mm (3.94 in.) mark from the ignited end, time of burning of 75 mm (3 in.) and average burning rate (in in./min or mm/min) are reported. If the specimen does not burn 100 mm, time and extent of burning are measured and reported along with a pattern of burning and/or fl ame self-extinguishing. There should be no forced or induced draft allowed during the test.

Precision of the test procedure is usually fair. ASTM D 635–03 lists examples for several different plastics, among them are polyethylene, ABS (acrylonitrile-butadiene-styrene), and acrylic, tested by eleven laboratories, using three specimens for each material (Table 14.10).

For polyethylene, average rate of linear burning was 15.2 ± 0.7 mm/min for within-laboratory tests and 15.2 ± 1.3 mm/min for between-laboratory tests. For ABS, it was 27.9 ± 2.1 mm/min for within-laboratory tests and 27.9 ± 4.1 mm/min for between-laboratory tests. For acrylic, it was 29.7 ± 1.7 mm/min and 29.7 ± 2.2 for within- and between-laboratory tests, respectively.

Note: ASTM E 1321 “Standard test method for determining material ignition and fl ame spread properties” is a different test in which a vertically oriented sample is employed. This test is not in a general use in plastic and WPC industry.

ASTM D 1929 “Standard Test Method for Determining Ignition Temperature of Plastics”

The ASTM fi re test procedure describes a laboratory determination of the fl ash ignition temperature (FIT) and spontaneous ignition temperature, or self-ignition temperature (SIT) of plastics and composites using a hot-air furnace. FIT is the minimum temperature at which suffi cient fl ammable gases are emitted to ignite by a

TABLE 14.10 Average linear burning rate

PlasticSpecimen thickness,

mm (in)Average rate of linear burning,

mm/min (in/min)

Polyethylene 3.0 (0.118) 15.2 (6.0)Acrylonitrile-butadiene-styrene 3.2 (0.126) 27.9 (11.0)Acrylic 3.0 (0.118) 29.7 (11.7)

pilot fl ame. SIT is the minimum temperature at which ignition occurs in the absence of any additional fl ame ignition (pilot) source.

Test values serve to rank materials according to ignition susceptibility under the actual use conditions. The procedure notes that specimens containing high levels of inorganic fi llers are diffi cult to evaluate; also, that the same material tested in differ-ent forms may give different results.

The ASTM procedure describes in detail the hot-air ignition furnace with acces-sories, consisting primarily of an electrical heating unit, air source, specimen holder, thermocouples, pilot fl ame, and timing device.

A specimen may be in the form of pellets, powder, sheet, fi lm, plastic cellular, or com-posite materials, with a specimen weight of 3.0 ± 0.2 g. The ASTM procedure describes in detail cutting or folding sheet or fi lm materials and conditioning test specimens.

The temperature of 400�C shall be used when no prior knowledge of the probable fl ash ignition temperature range is available. Other starting temperatures may be selected when information of the materials is available. The only principal differ-ence between FIT and SIT procedures is that the second one is conducted without the pilot fl ame. At the end of the fi rst 10 min of the heating, depending on whether ignition has or has not occurred, temperature shall be lowered or raised, and the test shall be repeated with a fresh specimen. The lowest air temperature at which a fl ash or self- ignition is observed during the 10-min period is the fl ash- or selfi gnition temperature.

Precision of FIT and SIT measurements is usually fair. ASTM D 1929–96 lists examples for several different plastics; among them are PVC, polystyrene, nylon, polyurethane, and phenol–formaldehyde resin (see Tables 14.11 and 14.12), tested by seven laboratories, using three replicates of each material. “Repeatability” in this case is the difference (in�C) between two averages, each one determined from three specimens of identical test material, using the same apparatus by the same analyst within a short time interval.

“Reproducibility” in this case is the difference (in�C) between two averages, each one determined from three specimens of identical test material, found by two operators working in different laboratories.

TABLE 14.11 Flash ignition temperature (FIT)

Plastic Physical formAverage FIT,

�C (�F)Repeatability

(�C)Reproducibility

(�C)

Phenol–formaldehyde resin

Solid bar 430(806) 9 117

Polyamide 6 Granules 413(775) 8 38Polystyrene Granules 378(712) 10 27Polyurethane

foam25 mm(1 in.)

thickness349(660) 12 66

PVC fi lm 0.15 mm(6 mills) thickness

327(621) 11 45



One can see that self-ignition temperature is higher than fl ash ignition, which is understandable, as pilot fl ame makes the ignition occurs faster. However, a difference between these temperatures varies signifi cantly between 21�C for polyurethane foam and 111�C for PVC fi lm.

ASTM E 84, “Standard Test Method for Surface Burning Characteristics of Building Materials”

This ASTM fi re test large-scale procedure describes determination of the relative burning behavior of the material in a form of a 24-ft long panel. The test is conducted with the specimen in the ceiling position with the surface to be evaluated exposed face down to the ignition surface. The specimen shall be either self-supporting by its own structural quality or supported from its front or the backside.

Two separate (and not necessarily related) readouts of the test are (a) fl ame spread along the surface of the specimen as a distance traveled by the boundary of a zone of fl ame over time and (b) smoke developed as a change in optical density (as a progress curve of light absorption percent) between the light source and the photoelectric cell mounted in the vent pipe. These data are used to calculate the respective FSI and SDI as described in the ASTM test procedure. The indexes are calculated as relative values to those of select grade oak (FSI arbitrarily set as 100) and inorganic reinforced cement board (FSI set as 0) surfaces under the specifi ed conditions.

The procedure notices that some materials melt or drip to such a degree that they interfere with the continuity of the fl ame and result in an apparent low FSI.

The test method exposes a 24-ft (7.32-m) long by 20.25-in. (0.514-m) wide speci-men to a controlled air fl ow and adjusts the observed fl ame spread to that with the select grade oak for which the fl ame spreads the entire length of the specimen in 5½ min. The specimen may consist of sections joined together.

The ASTM tests describe in detail the fi re test chamber (the so-called 25-ft cham-ber), its insulation, dimensions, observation windows, lid assembly, gas burners, air

TABLE 14.12 Self-ignition temperature (SIT)

Plastic Physical formAverage SIT,

�C(�F)Repeatability,

(�C)Reproducibility,

(�C)

Phenol–formaldehyde resin

Solid bar 482(900) 14 103

Polystyrene Granules 458(856) 12 59Polyamide 6 Granules 439(822) 31 56PVC fi lm 0.15 mm(6 mills)

thickness438(820) 13 64

Polyurethane foam 25 mm(1 in.) thickness

370(698) 11 61

intake, thermocouples, exhaust, and the photometer system (including a lamp and photocell) mounted in the vent pipe.

The FSI is calculated as follows. The end of the ignition fi re—according to the ASTM procedure—shall be considered as being 4½ ft from the burners. Hence, fl ame spread distance shall be determined as the observed distance minus 4½ ft. Now, suppose the fl ame spreads 10 ft in 2.5 min, then remains for eight more min-utes at the same 10-ft mark, and fi nally spreads again for the subsequent 2 min from 10-ft mark to 20-ft mark. The total area under that curve, given in the ASTM proce-dure, is equal to 90 ft min. The procedure says that in this case (an area is less than 97.5 ft min) the FSI is equal to 90 � 0.515 46 ft min.

If, suppose, this area under the curve is a little higher, say, 100 ft min (or any area higher than 97.5 ft min), the FSI in this case would be equal to 4900/(195–100) 52 ft min, where 4900 and 195 are constants, prescribed by the procedure.

The SDI is calculated in a similar manner, normalized by the area under the curve for red oak, multiplied by 100 and rounded to the nearest multiple of 5. For indexes of 200 and higher, the calculations shall be rounded to the nearest 50 points.

Precision of the test procedure is usually fair, with larger deviations for lower FSI fi gures. ASTM E 84–01 lists examples of FSI for six different materials, among them two samples of plywood (one was treated with fl ame retardant), one gypsum board, two plastic foams, and one composite panel. The determi-nations were made in eleven laboratories with four replicates of each material (Table 14.13).

“Repeatability” in this case is the difference (in FSI) between two averages, each one determined from four specimens of identical test material, using the same ap-paratus by the same analyst within a short time interval. “Reproducibility” in this case is the difference (in FSI) between two averages, each one determined from four specimens of identical test material, found by two operators working in different laboratories.

TABLE 14.13 Flame spread index (FSI). Within-laboratory and between-laboratory data

Material FSI, mean value

Standard deviation

Repeatability Reproducibility

Douglas Fir plywood 91 15 23Rigid polyurethane foam 24 3 5Fire retardant treated Douglas Fir

plywood17 3 6

Composite panel 17 2 4Type X gypsum board 9 2 3Rigid Polystyrene foam 7 1 4



ASTM E 1354, “Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter”

This standard test method is listed in ASTM D 7032 “Standard specifi cation for es-tablishing performance rating for WPC deck boards and guardrail systems (guards or handrails)” as a reference to “fi re performance properties other than fl ame spread.” The ASTM E 1354 fi re test procedure describes determination of the ignitability, heat release rates, visible smoke development, and other related characteristics of materials and products. Specimens shall be exposed to heating fl uxes in the range of 0–100 kW/m2. The rate of heat release (i. e., the heat evolved from the specimen per unit of time) is determined by measuring the oxygen consumption, and smoke development is measured by decrease of optical density (or light transmission) of light by combustion product stream. Ignitability is determined as a measurement of time from initial exposure to time of sustained fl aming (of at least 4 s), provided that ignition is initiated by electric spark. Specimens shall be tested in a horizontal position. Flaming of less than 4 s duration is identifi ed in this ASTM procedure as fl ashing or transitory fl aming.

In other part, this ASTM test is based on the observation that, generally, the net heat of combustion is directly related to the amount of oxygen required for combustion. The relationship is that approximately 13,100 kJ of heat are released per 1 kg (2.2 lb) of oxygen consumed. The procedure prescribes burning of speci-mens in ambient air conditions, while they are subjected to a specifi ed external heat fl ux. Burning may be either with or without spark ignition. The primary measurements are oxygen concentrations and exhaust gas fl ow rate. The ASTM procedure describes in detail the test apparatus, specimen mounting, gas sam-pling, heat fl ux meter, and so on. Regarding smoke release measurements, they are conducted using a helium–neon laser, photodiodes as main beam and refer-ence detectors, and appropriate electronics to derive the extinction coeffi cient and to set the zero reading. The smoke obscuration measuring system is attached to the exhaust duct.

The ASTM procedure specifies test size as 100 � 100 mm, up to 50 mm thick (4-in. � 4-in. up to 2-in. thick). Other sizes are also considered in the procedure in case of greater or smaller thickness of the tested material. The procedure describes calculations of heat release, mass-loss rate, effective heat of combustion, and smoke obscuration. For the latter, the extinction coefficient is calculated as

k (1/L) � ln(I0/I)

wherek the smoke extinction coeffi cient (meter1),L optical beam path length (meter),I actual beam intensity,I0 beam intensity with no smoke.

The ASTM test requires to report smoke obscuration as the average specifi c ex-tinction area (m2/kg) for each specimen. The average specifi c extinction area (σ, m2/kg) is calculated as the volume exhaust fl ow rate (V, m3/s), measured at the location of the laser photometer, multiplied by the smoke extinction coeffi cient (k, m1) and by the sampling time interval (∆t, s), divided by the specimen mass loss (∆m, kg), and averaged for repeated tests.

σ Vk∆t/∆m

The ASTM procedure gives a range for average specifi c extinction areas for a number of different materials, which is between 30 and 2200 m2/kg. Among those materials were fi re retardant treated ABS, polyethylene, PVC, polyisocyanurate, polyurethane, and gypsum board.

E 162 “Standard Test Method for Surface Flammability of Materials Using a Radiant Heat Energy Source”

This ASTM test will be briefl y described here. The test is not intended for use as a basis of rating for building code purposes, as, for example, ASTM E 84. The purpose of the test is to determine the relative surface fl ammability performance of various materials under specifi c test conditions under a radiant heat source.

A radiant 12 in. by 18 in. panel is preheated with a gas–air mixture to a radiant output equal to that obtained from a black body of the same dimensions operating at 670�C (1238�F). A test specimen 6 in. by 18 in. is suitably mounted facing the radian panel and being inclined as specifi ed in the ASTM standard. The specimen is ignited at the top by a pilot fl ame, and the material burns downward. The operator records the fl ame progression at 3, 6, 9, 12, and 15 in. interval marks measured from the top of the sample. The operator also records the maximum temperature increase resulting from the burning sample measured by eight thermocouples located above the tested sample. The FSI is derived as

Is Fs � Q

whereIs the fl ame spread indexFs the fl ame spread factorQ the heat evolution factor.

The ASTM procedure describes a calculation of the Fs, which is determined by the speed at which the fl ame front burns down the specimen. The higher the Fs value, the faster the specimen burns. The procedure also describes determination of the Q from the maximum temperature developed in the stack above the burn-ing sample. The hotter the fl ame during the burning, the higher the heat evolution factor.



Note of the author: To illustrate values obtained according to the above ASTM procedure, the following table gives an example of two composite materials, one of which contains two-thirds of rice hulls and one-third of HDPE, another contains one-third of rice hulls, one-third of a mineral fi ller and one-third of HDPE (Table 14.14).

E 662 “Standard Test Method for Specifi c Optical Density of Smoke Generated by Solid Materials”

This ASTM test will be briefl y described here. The test is not intended for use as a basis of rating for building code purposes. The procedure covers measuring the smoke generated by solid materials and assemblies in thickness up to 1 in. The test is based on decrease of optical density of a light beam by smoke accumulated within a closed chamber due to nonfl aming pyrolytic decomposition and fl aming combustion. Both fl aming and nonfl aming exposures are conducted. Test results are expressed in terms of specifi c optical density.

The ASTM method uses an electrically heated radian energy source of a specifi ed power, positioned over a vertically mounted specimen. This exposure provides the nonfl aming exposure of the test. For the fl aming condition, a specifi ed fl ame burner is used.

The test specimens are exposed to the fl aming and nonfl aming conditions within a closed 18-ft3 chamber, equipped with a photometric system.

Specimens of 3 in. by 3 in. size and up to 1 in. by thickness are predried for 24 h at 60�C (140�F) and then conditioned to constant weight at ambient temperature. The ASTM test describes calculations to obtain specifi c optical density of smoke.

Note of the author: To illustrate values obtained according to the above ASTM procedure, the following table gives an example of two composite materials, one of which contains two-thirds of rice hulls and one-third of HDPE, another contains one-third of rice hulls, one-third of a mineral fi ller and one-third of HDPE. During the fl aming mode both samples ignited at about 10 s and burned for approximately 10 min (Composite 1) and 14 min (Composite 2). The data are average from three nonfl aming and three fl aming measurements (Table 14.15).

TABLE 14.14 Flame Spread Index (FSI), Flame Spread Factor (FSF), and Heat of evolution values (determined according to ASTM E 162) for two HDPE-based composite materials, one fi lled with rice hulls, another with rice hulls and a mineral fi ller. Detailed on the compositions are given on page 484. Data by the author.

Material Flame spread index

Flame spread factor

Heat of evolution

Composite 1 (HDPE and rice hulls)

226 ± 11 4.3 ± 0.2 52.0 ± 0.8

Composite 2 (HDPE, rice hulls, and a mineral fi ller)

164 ± 15 3.6 ± 0.4 46 ± 3

FIRE PERFORMANCE OF COMPOSITE DECKS AND DECK BOARDS 485

FIRE PERFORMANCE OF COMPOSITE DECKS AND DECK BOARDS

UC Forest Products Laboratory (UCFPL) has undertaking fi re performance testing of neat plastic and WPC deck boards. The testing was conducted in 2002. Table 14.16 and Figures 14.1 through 14.10 summarize and illustrate main results of the test.

TABLE 14.15 Smoke Development Index (SDI) determined in fl aming and nonfl aming conditions according to ASTM E 662, for two HDPE-based composite materials, one fi lled with rice hulls, another with rice hulls and a mineral fi ller. Detailed on the compositions are given on page 484. Data by the author.

Smoke developed index

Material Nonfl aming Flaming

Composite 1 (HDPE and rice hulls) 392 ± 2 345 ± 45Composite 2 (HDPE, rice hulls, and

a mineral fi ller)298 ± 100 351 ± 72

Figure 14.1 Plastic lumber Eon (100% polystyrene), channeled deck board, before and after 2.5 min of a fi re test (by permission from the University of California Forest Products Laboratory).


TABLE 14.16 Underdeck fl ame impingement test results (UCFPL)

Deck board Material, shape

The time of board collapse or runaway

combustion Type of failure

Redwood Wood No degradation effects No failure in 40 min

Eon 100% polystyrene, foamed, channeled, density 0.80 g/cm3

Less than 4 min Began dropping fl aming debris; combustion accelerated

Maxituf 100% HDPE, solid, density 0.94 g/cm3

Less than 4 min Began dropping fl aming debris; combustion accelerated

EverNew 100% PVC, hollow, density 1.44 g/cm3

Less than 4 min Collapsed

TimberTech 37% HDPE, channeled, 15% minerals, 48% wood fi ber, density 1.22 g/cm3

In less than 4 min began dropping fl aming debris, collapsed in 9 min

Began dropping fl aming debris; combustion accelerated; board collapsed

ChoiceDek 50% polyethylene, 50% wood fi ber, slightly channeled, density 0.91 g/cm3

In less than 4 min began dropping fl aming debris, collapsed in 14 min

Began dropping fl aming debris; combustion accelerated; board collapsed

Nexwood 42% HDPE, hollow, 46% rice hulls, 12% minerals, density 1.17 g/cm3

In 10 min began dropping fl aming debris, collapsed in 14 min

Began dropping fl aming debris; board collapsed

Bedford #1 100% HDPE, solid, density 0.97 g/cm3

In less than 2 min began dropping fl aming debris, combustion accelerated in 17 min

Began dropping fl aming debris; combustion accelerated

Ecoboard 100% polyethylene, foamed, density 0.85 g/cm3

In less than 2 min began dropping fl aming debris, combustion accelerated in 22 min

Began dropping fl aming debris; combustion accelerated

Trex 50% LDPE/HDPE, 50% wood fi ber, solid, density 0.92 g/cm3

In 20 min began dropping fl aming debris

Began dropping fl aming debris

Rhino Deck 35% HDPE, 65% wood fi ber, solid, density 1.08 g/cm3

In 22 min began dropping fl aming debris

Began dropping fl aming debris

SmartDeck 35% polyethylene, 65% wood fi ber, solid, density 1.10 g/cm3

No degradation effect No failure in 40 min

WeatherBest solid

28% HDPE, 60% wood fl our, 12% talc � phenol-formaldehyde resin; solid, density 1.20 g/cm3


WeatherBest hollow

Same No degradation effect No failure in 40 min

Bedford #2 85% HDPE, 15% minerals, solid, density 1.06 g/cm3



Figure 14.2 Wood-plastic composite TimberTech (37% HDPE, 15% minerals, 48% wood fi ber, density 1.22 g/cm3), channeled deck board, before and after 9 min of a fi re test (by permission from the University of California Forest Products Laboratory)

Figure 14.3 Wood-plastic composite ChoiceDek (50% polyethylene, 50% wood fi ber, den-sity 0.91 g/cm3), slightly channeled deck board, before and after 14 min of a fi re test (by permission from the University of California Forest Products Laboratory).


Figure 14.5 Wood-plastic composite Trex (50% LDPE, 50% wood fi ber, density 0.92 g/cm3), solid deck board, before and after 40 min of a fi re test (by permission from the Univer-sity of California Forest Products Laboratory).

Figure 14.4 Wood-plastic composite Nexwood (42% HDPE, 46% wood fi ber, 12% miner-als, density 1.17 g/cm3), hollow deck board, before and after 14 min of a fi re test (by permis-sion from the University of California Forest Products Laboratory).


Figure 14.6 Wood-plastic composite Rhino Deck (35% HDPE, 65% wood fi ber, density 1.13 g/cm3), solid deck board, before and after 22 min of a fi re test (by permission from the University of California Forest Products Laboratory).

Figure 14.7 Wood-plastic composite SmartDeck (35% polyethylene, 65% wood fi ber, den-sity 1.10 g/cm3), solid deck board, before and after 40 min of a fi re test (by permission from the University of California Forest Products Laboratory).


Figure 14.9 Wood-plastic composite WeatherBest (33% polyethylene, 60% wood fi ber, 7% minerals, density 1.20 g/cm3), hollow deck board, before and after 15 min of a fi re test (by permission from the University of California Forest Products Laboratory).

Figure 14.8 Wood-plastic composite WeatherBest (33% polyethylene, 60% wood fi ber, 7% minerals, density 1.20 g/cm3), solid deck board, before and after 40 min of a fi re test (by permission from the University of California Forest Products Laboratory).

REFERENCES

R.H. White and M.A. Dietenberger. Fire safety. In: Wood Handbook, Forest Products Society, Madison, WI, 1999, Chapter 17, p. 17–3.

C. Vasile and M. Pascu. Practical Guide to Polyethylene. Rapra Technology, Rapra Technology Ltd. UK, 2005, p. 93.

R.H. White and M.A. Dietenberger. Fire safety, In: Wood Handbook, Forest Products Laboratory, 1999, Chapter 17, p. 17–7.

J. Troitzsch. Plastics Flammability Handbook. Principles, Regulations, Testing, and Approval. 3rd edition, Hanser, Munich-Cincinnati, 2004, p. 18.

Natural & Wood Fiber Composites, Vol. IV, No. 9, Principia Partners, Cleveland, OH, September 2005, p. 2,

J. Troitzsch. Plastics Flammability Handbook. Principles, Regulations, Testing, and Approval. 3rd edition, Hanser, Munich-Cincinnati, 2004, p. 146.

J. Andrews. Flame retardants for the future today. In: 15th International Conference ADDITIVES 2006, Plastics Additives for Special Effects, ECM, Plymouth, MI, Las Vegas, NV, January 30–February 1, 2006.

P. Moy. Recyclability of FR-PC/ABS composites using non-halogen flame retar-dants. In: 15th International Conference ADDITIVES 2006, Plastics Additives for Special Effects, ECM, Plymouth, MI, Las Vegas, NV, January 30–February 1, 2006.

1.

2.

3.

4.

5.

6.

7.

8.

REFERENCES 491

Figure 14.10 Redwood (density 0.40 g/cm3), solid deck board, before and after 40 min of a fi re test (by permission from the University of California Forest Products Laboratory).


R.B. Dawson and S.D. Landry. The issues & regulatory status for fl ame retardants. In: 15th International Conference ADDITIVES 2006, Plastics Additives for Special Effects, ECM, Plymouth, MI, Las Vegas, NV, January 30–February 1, 2006.

Chem. Eng. News, American Chemical Society, Washington, DC, June 26, 2006, p. 8.

R.L. Markezich. Clorine containing fl ame retardants. In: 15th International Conference ADDITIVES 2006, Plastics Additives for Special Effects, ECM, Plymouth, MI, Las Vegas, NV, January 30–February 1, 2006.

J. Troitzsch. Plastics Flammability Handbook. Principles, Regulations, Testing, and Approval, 3rd edition, Hanser, Munich-Cincinnati, 2004, p. 147.

G. Beyer. Nanocomposites offer new way forward for fl ame retardants. Plastic Addit. Compd., 2005, 7(5), p. 32–35.

G. Guo, Y.H. Lee, Y.S. Kim, C.B. Park, and M. Sain, Flame retarding effects of nano-clay on wood-fi ber composites, In: The Global Outlook for Natural Fiber & Wood Composites 2004, Intertech, Portland, ME, New Orleans, LA, December 8–10, 2004.

J. Innes, A. Innes, M. Wajer, D. Smith, and L. Granada. Nano materials as fl ame retardants in metal hydrate FR formulations. In: 15th International Conference ADDITIVES 2006, Plastics Additives for Special Effects, ECM, Plymouth, MI, Las Vegas, NV, January 30–February 1, 2006.

9.

10.

11.

12.

13.

14.

15.

Documents

Wood-Plastic Composites || Flammability and Fire Rating of Wood–Plastic Composites