DuPont™ Neoprene Types of Neoprene — Dry Rubber Applications

Technical Information — Rev. 8, September 2010

Introduction This technical bulletin is intended to provide guidance in selecting the appropriate type of Neoprene for development of compounds for specific applications. In addition to providing recommendations for achieving certain physical properties, consideration is given to the selection of types of Neoprene best adapted to specific processing and storage conditions.

Neoprene Polychloroprene The major monomer component in every type of Neoprene polychloroprene that is manufactured by DuPont, is chloroprene (2-chloro-1,3-butadiene). The monomer backbone structure of polychloroprene can be modified by copolymerizing chloroprene with sulfur, 2,3 dichloro-1,3-butadiene, or other monomers to yield a family of materials with a broad range of chemical and physical properties. By proper selection and formulation of these polymers, the compounder can achieve optimum performance for a given end-use.

Basic Characteristics of DuPont™ Neoprene Neoprene polychloroprene is a multipurpose elastomer that has a balanced combination of properties. All types of Neoprene have these inherent characteristics:

• Resist degradation from sun, ozone, and weather. • Perform well in contact with oils and many chemicals. • Remain useful over a wide temperature range. • Display outstanding physical toughness. • Are more resistant to burning than exclusively hydrocarbon rubbers.

Selecting the Proper Type Three general types of Neoprene are available for dry rubber applications, Neoprene G, W, and T types. These elastomers offer a broad range of physical properties and processing capabilities so that users can formulate to specific requirements. Raw polymer and vulcanizate properties of each of the general types are displayed in Table 1 and in Figure 1.

Neoprene compounds can frequently be modified for new applications simply by changing the type of Neoprene used. For example, a crystallization-resistant type can be substituted for a general purpose type to adapt a compound for low-temperature applications.

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Table 1 . Characteristics of DuPont™ Neoprene Types G Types W Types T Types

Raw Polymers Limited Storage Stability Excellent Storage Stability Excellent Storage Stability

Peptizable to Varying Degrees Non-Peptizable Least Nerve

No Acceleration Necessary Accelerator Required Cure Flexibility

Accelerator Required Cure Flexibility

Fast Curing, but Safe Processing

Best Extrusion, Calendering Performance

Vulcanizates Best Tear Strength

Best Compression Set Resistance

Best Flex Properties Similar to W Types

Best Resilience Best Heat-Aging

Figure 1. Neoprene Selection Guide

NEOPRENEGood weatherabilityOil resistantResilientExcellent tensiles

GNAPeptizableGood tear & flexNo accelerator required

GWLess peptizableGood heat & setGood flow

GRTBest tackLow temperature flexBest frictioning

WHV-100Highly extended compounds

WHVExcellent for very highly extendedcompounds

WExcellent storageBest heat & setNeeds accelerator

WRTBest low temperature

WBIn blends for better Extrusion & calendering

W-M1Lower viscosity WD

Excellent for very highly extendedcompounds

TW-100Highly extendedcompounds

TWBetter extrusion &calendering

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Polymer Stability and Storage Considerable care is taken by DuPont to minimize the heat history of DuPont™ Neoprene before it is shipped and delivered. During manufacture, Neoprene is cooled as rapidly as possible after drying. Depending upon the grade, Neoprene polymers are stored in warehouses at 7 °C or 18 °C. During warmer months, Neoprene is sometimes shipped to consumers or ports of embarkation in insulated freight cars or trucks. Consumers should make every effort to store Neoprene, especially G types, in cool warehouse locations. Also, to avoid accumulation of old product, inventories should be kept to a minimum and the polymer used in the same order as delivered, i.e., “First-In-First-Out.”

Although it is good practice to store all types of Neoprene in a cool and dry environment, DuPont™ Neoprene W types will remain stable to viscosity changes longer and under more widely varying conditions than G types. The excellent storage stability of Neoprene W types results from the absence of components that contribute to instability, such as sulfur and thiuram disulfide.

DuPont™ Neoprene T types exhibit the same excellent storage stability and minimal sensitivity to heat history (in the absence of a cure accelerator) as W types. For more information on polymer storage and stability, refer to the DuPont technical bulletin, “Guidelines for Neoprene Storage and Useful Life”.

Crystallization Resistance Crystallization is a common phenomenon in polymer types that have high proportions of long chain molecules of significant regularity. Certain grades of Neoprene are designed to minimize chain regularity by addition of comonomers or polymerization at higher temperatures.

DuPont™ Neoprene WRT and WD are designed for use in finished products that must remain flexible for long periods at low temperatures. The excellent crystallization resistance of these types helps counteract the increase in rate of crystallization-induced stiffening that is caused by ester plasticizers. Therefore, high levels of ester plasticizers can be tolerated for increased resistance to thermal stiffening.

DuPont™ Neoprene GRT has the greatest resistance to crystallization of any of the G types. Raw polymer and stocks prepared from Neoprene GRT remain soft and flexible for long periods, particularly at low temperatures. Due to its excellent tack retention, Neoprene GRT is the preferred type of Neoprene for friction compounds and other applications requiring good building properties.

Compounding Compounding of all types of Neoprene manufactured by DuPont is discussed in the technical bulletin “A Guide to Grades, Compounding and Processing of Neoprene.”

Neoprene W types are available in a variety of viscosity grades, thus providing the compounder a wide choice in compound design. The high viscosity grades of both general purpose and crystallization-resistant W types can be highly extended with fillers and plasticizers. The resulting compounds will have workable compound viscosity and useful vulcanizate properties.

Curing systems for Neoprene W types are available that not only provide processing safety and acceptable cure rate, but that also achieve desired vulcanizate properties such as optimum compression set resistance.

Generally, the response of Neoprene G types to compounding ingredients is similar to that of Neoprene W types. However, G type compounds differ from W and T type compounds in several ways:

• Addition of chemical peptizers causes softening • Mechanical shear causes softening • Can be cured with metal oxides alone; organic accelerators are not required • Less plasticizer is needed to prepare compounds in a workable viscosity range

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DuPont™ Neoprene T types should be compounded similarly to W types with respect to filler and plasticizer loading, anti-degradant protection, and curing systems. However, for the same loading, a compound based on a T type will be slightly higher in viscosity, and vulcanizates will be slightly higher in modulus and hardness compared to those based on the corresponding W type. Additional plasticizer (usually an additional 3–4 parts) can be used to balance these properties, if desired.

Comparison of Individual Types Neoprene G, W, and T types are available in a number of different grades. Table 2 can be used to qualitatively evaluate physical properties of Neoprene grades, including raw polymer, uncured compound, and vulcanizate properties. Table 3 provides a more quantitative summary of the product line, describing polymer viscosities, comonomers, crystallization rates, and raw polymer stabilities. By selecting the most important properties required for end-use, the compounder can choose the appropriate type(s) for compound development.

Table 2. Relative Property Comparisons of Neoprene Types Properties GW GNA GRT W W M1 WHV 100 WHV WRT WD WB TW TW 100

Raw Polymer Crystallization Resistance VG G VG P P P P E E P P P Extendable G G G G G VG E G E G G VG Peptizable G E E P P P P P P P P P Viscosity* Lo Lo Lo Lo VLo M Hi Lo Hi Lo Lo M Stability G G G E E E E E E E E E

Uncured Compound Cure Rate E E E VG VG VG VG G G VG VG VG Green Strength VG G G VG P E E G E G VG E Processability G G G G G VG VG G VG E E E

Vulcanizate

Compression Set Resistance G P P E E E E E E E E E Good Flex E E E G G G G G G P G G Good Tear E E E G G G G G G P G G Heat-Aging VG G G E E E E E E E E E Resistance Low-Temperature Properties G G VG G G G G E E G G G

Property Rating: E = Excellent, VG = Very Good, G = Good, S = Satisfactory, P = Poor

*Viscosity Rating: Hi = High, M = Medium, Lo = Low, VLo = Very Low

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Table 3. Comparison Chart — DuPont™ Neoprene Types

Family Characteristics Type Comonomer* Polymer Stability

**Mooney Viscosity

Crystalli-zation Rate Distinguishing Features

G Types GW Sulfur Good 37–49 Slow Best tear and flex

Best G type for heat-aging and compression set resistance Very slightly peptizable Contains thiuram

Raw Polymers Limited storage Peptizable to varying degrees Fast curing, but safe processing No accelerators necessary

GNA M1 M2

Sulfur

Good

42–54 47–59

Medium

Staining stabilizer Contains thiuram

Vulcanizates Best tear strength Best flex Best resilience

GRT M1 M2

Sulfur/ACR

Good

34–46 40–52

Slow

Best tack Crystallization resistance Contains thiuram

W Types

W M1 W WHV 100

None None None

ExcellentExcellentExcellent

34–42 40–49

90–105

Fast Fast Fast

General purpose-low viscosity General purpose-std. viscosity General purpose-med. high viscosity

Raw Polymers Excellent storage stability Non-peptizable

WHV WRT

None

ACR

Excellent

Excellent

106–125

41–51

Fast

Very Slow

General purpose-high viscosity Very slow crystallizing Slower curing than W

Vulcanizates Best compression set resistance Best heat-aging

WD WB

ACR

None

Excellent

Excellent

100–120

43–52

Very Slow

Medium

High-viscosity WRT Contains high percentage of gel for processing Vulcanizate properties reduced Generally used in blends

T Types

Raw Polymers Excellent storage stability Least verve Fast processing

TW TW 100

Gel

Gel

Excellent

Excellent

42–52

82–99

Fast

Fast

Gel-containing for good processing Vulcanizate properties similar to W types Higher viscosity form of TW

Vulcanizates Properties similar to W types

*Principal Monomer is chloroprene; ACR = 2,3-dichloro-1,3-butadiene; Gel = gel-forming comonomer

**ML 1 + 4 at 100 °C, DPE Test Method N200.5700

Neoprene G Types General Characteristics During emulsion polymerization of DuPont™ Neoprene G types, chloroprene monomer is copolymerized with sulfur to form a high molecular weight copolymer. The sulfur atoms are present in the polymer chain in clusters or as single atoms situated between the chloroprene (CD) segments. This is represented schematically below:

— (CD)n — Sx — (CD)m —

where Sx represents one or more sulfur atoms; m and n may be the same or different integers.

After the polymerization is stopped, combinations of thiuram disulfides and dithiocarbamates are added to reduce the molecular weight to provide the desired Mooney viscosity. This polymerization process results in production of polymers having much broader molecular weight distributions than are found in Neoprene W or T types. In addition, raw polymer storage stability of G types is more limited than that of W or T types.

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Processing Characteristics DuPont™ Neoprene G types break down, or soften, under mechanical shear experienced during mixing and forming operations to a much greater extent than do the W or T types. Breakdown can be increased by the addition of chemical peptizers. This characteristic provides a means to facilitate a workable viscosity in highly loaded stocks while utilizing a minimum of plasticizer. Breakdown, i.e., peptization, also causes the G types to be tackier than other Neoprene types. DuPont™ Neoprene GW peptizes to a lesser extent than other G types. Compounds of Neoprene GW have higher viscosities, are less sticky, and have less building tack than similarly loaded compounds of other G types.

In order to prevent scorch and minimize heat history, good temperature control should be maintained during mill or internal mixing, warming, extruding, and calendering operations. Use of refrigerated water is particularly helpful, especially during summer. Batch stock should be sheeted (9.5 mm thick or less), and should be cooled as quickly as possible with a water dip or spray, followed by air circulation to evaporate all traces of water. Sheets of freshly mixed stock should not be stacked until they have been cooled to temperatures of 32 °C or below. With respect to G types, heat history should be kept to a minimum to guard against scorch. Even very slight scorching may introduce sufficient nerve into a stock so that mold flow and extrusion or calendaring will be adversely affected.

Compounds of Neoprene G types have less nerve than those of W types (except Neoprene WB), and consequently shrink less and sheet out more smoothly on calendering. Extruded surfaces are smoother and better defined. With respect to these qualities, Neoprene G types approach, but do not quite equal, gel-containing polymers like T types, or blends containing 20% or more Neoprene WB.

Peptization and Mechanical Breakdown Peptization is a process by which molecular weight of polymers is reduced by chemical action, mechanical work, or a combination of both. Peptization of an elastomer produces a workable compound viscosity at a high filler loading without a reduction in vulcanizate hardness and strength.

Neoprene GW is peptizable, but not to the same extent as other Neoprene G types because it contains fewer — Sx — structures where x is greater than 1. As shown in Table 4, peptization reduces the viscosity of Neoprene GW by only 5–10 Mooney units, even with chemical agents, while the viscosities of other Neoprene G types are reduced by up to 30 Mooney units. Compounds of Neoprene GW have a higher viscosity than similarly loaded compounds based on Neoprene GNA, or GRT and, therefore, are less sticky and have less building tack. Figure 2 illustrates the peptization rate of Neoprene GW versus other Neoprene types in a Brabender Plastograph. Note the final viscosity of Neoprene GW is intermediate between Neoprene W and the other Neoprene G types due to the limited breakdown of the polymer.

In DuPont™ Neoprene GNA and GRT, a significant amount of uncleaved — Sx — (where x is greater than 1) units remain in the polymers after isolation. Thiuram disulfide remains in the polymer as well, and through mechanical work, the viscosities of these G grades will soften further.

Curing and Vulcanizate Properties Neoprene G types can be cured with metal oxides alone. In addition, cure accelerators can be used and may be desirable to develop certain properties, but accelerators are not required.

Neoprene, G type compounds are more susceptible to reduction in scorch time by accumulated heat history than are compounds based on other types of Neoprene.

Vulcanizates based on Neoprene G types generally exhibit greater tear strength and elongation, a snappier feel, and adhere better to natural rubber and SBR substrates.

Figure 2. Neoprene Peptization Rate

Table 4 Peptization of Neoprene

Grade of Neoprene GW GNA GRT W Mooney Viscosity, ML 1 + 4 at 100 °C Original 43 39 35 40 Peptized* 33 8 10 41 *Samples peptized with 0.63 phr of Vanax® 552 for 15 min at initial temperature of 70 °C.

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When to Use G Types Compounders choose DuPont™ Neoprene G types for use in applications where building tack is important in fabricating the final product and in situations where the end-use involves severe flexing or other dynamic stresses, and minimum compression set is not required.

Neoprene G types are used when a compound requires high loadings with a minimum of plasticizer. Because G types break down or soften when subjected to shear during mixing, workable viscosities can be achieved in this type of compound.

When organic accelerators are not appropriate for use, such as in some compounds requiring FDA approval, G types may be cured with metal oxides alone.

Neoprene G types, and particularly DuPont™ Neoprene GRT, are preferred when good friction characteristics are desired. DuPont™ Neoprene GW is recommended for end uses when a good balance of dynamic and aging properties is desired.

DuPont™ Neoprene GNA Description DuPont™ Neoprene GNA is a sulfur-modified polychloroprene stabilized with a thiuram disulfide and a staining antioxidant. It should not be used in applications where resistance to staining or discoloration of finishes is necessary.

Processing and Performance Features Moderate Polymer Breakdown Neoprene GNA breaks down or softens under the mechanical shear imposed during mixing and produces smooth-processing compounds. It crystallizes more rapidly than Neoprene GRT, so Neoprene GNA compounds are less sticky and have somewhat less building tack than those containing GRT.

Vulcanizates Resistant to Flexing and Other Dynamic Stresses Properly compounded vulcanizates of Neoprene GNA have high resilience, tear strength, and flex cracking resistance.

DuPont™ Neoprene GRT Description Neoprene GRT is a sulfur-modified, crystallization-resistant polychloroprene stabilized with a thiuram disulfide and a nonstaining antioxidant. It is slower-crystallizing than other G types.

Processing and Performance Features Crystallization and Friction Characteristics Neoprene GRT exhibits the greatest resistance to crystallization of any Neoprene G type. The raw polymer, as well as stocks and vulcanizates prepared from Neoprene GRT, remain soft and flexible for a long period, particularly at low temperatures.

Neoprene GRT rapidly breaks down and becomes tacky under the mechanical shear imposed during mixing. In addition, because it is slow to crystallize, it remains tacky much longer than Neoprene GNA. Due to its excellent tack retention, Neoprene GRT is the preferred type of Neoprene for friction compounds and other applications requiring good building tack.

Cure Rate and Resistance to Flexing Compounds of Neoprene GRT do not require accelerators and can be cured with metal oxides. These compounds exhibit excellent processing safety, yet cure rapidly. Although not required, cure accelerators may be used and are advantageous for some applications.

Properly compounded vulcanizates of Neoprene GRT have high resilience, tear strength, and flex cracking resistance. These properties, combined with good building tack, have led to wide use of Neoprene GRT in composite structures that are subjected to severe dynamic stresses, such as power transmission belts.

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DuPont™ Neoprene GW Description Neoprene GW is a sulfur-modified polychloroprene stabilized with a thiuram disulfide. The crystallization rate of Neoprene GW is slightly faster than that of Neoprene GRT.

Processing and Performance Features Limited Polymer Breakdown

Neoprene GW breaks down to a lesser degree than other G types. Compounds based on Neoprene GW will, therefore, exhibit a higher viscosity than similarly loaded compounds based on Neoprene GNA or GRT. Because of the higher compound viscosity, stocks based on Neoprene GW are slightly less sticky and have slightly less building tack than stocks based on other G types.

Compounds of Neoprene GW have approximately the same viscosity as similarly loaded compounds of Neoprene W.

Vulcanizates Resistant to Flexing, Dynamic Stress, Heat-Aging, and Compression Set

Properly compounded vulcanizates of Neoprene GW have high resilience, and excellent flex cracking resistance, and the best tear strength of any vulcanized Neoprene type.

Vulcanizates of Neoprene GW retain their properties after heat-aging better than vulcanizates of other G types. Compression set resistance is significantly improved over that of other G types, although it is not as good as that of thiourea-cured W types.

DuPont™ Neoprene W Types General Characteristics Neoprene W polychloroprenes are chloroprene homopolymers or copolymers of chloroprene and 2,3-dichloro-1,3-butadiene. They do not contain elemental sulfur, thiuram disulfide, or other additives that are capable of decomposing to yield either free sulfur or a vulcanization accelerator. They do not contain any staining stabilizer. They have a more uniform molecular weight distribution than the G types. Neoprene W types have excellent raw polymer storage stability, considerably better than that of the G types.

Processing Characteristics Neoprene W types do not exhibit molecular weight reduction under mechanical shear or with chemical peptization. However, some reduction in viscosity may occur under high shear conditions. The degree of softening is greater for the high molecular weight polymers such as Neoprene WHV or WD. Neoprene W type compounds mix faster, have better mill release, and yield extrudates that are more resistant to distortion and collapse than compounds of GNA and GRT. There is less batch-to-batch variation in compound viscosity than with compounds of Neoprene GNA or GRT. Compounds of W types have less inherent building tack and greater nerve than compounds of the G types. The availability of various viscosity grades enables the compounder to select a polymer or blend of polymers that will provide a suitable compound viscosity for processing with virtually any loading.

Although the processing characteristics of compounds based on W types are generally good, they can be further improved (at the expense of some vulcanizate tensile strength, tear strength, and resistance to flex cracking) by incorporating a highly crosslinked gel form of polychloroprene, Neoprene WB, in the raw polymer. As the amount of gel component in the polymer increases, nerve decreases and extrudates exhibit smoother surfaces, better collapse resistance, and reduced shrinkage.

Considerable latitude in processing safety and cure rate is possible with the W types through selection of the type and amount of curatives, and by delaying addition of the accelerator. In addition to recognized accelerators, the materials most likely to impair bin storage stability are antioxidants and antiozonants.

Curing and Vulcanizate Properties Cure accelerators must be added to achieve practical cure rates and acceptable vulcanizate properties. Therefore, Neoprene W types offer considerable latitude in processing safety and cure rate through judicious choice of type and amount of accelerator. Before accelerators are added to the mix, Neoprene W compounds are much less susceptible to scorch due to heat history than compounds based on Neoprene G types.

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DuPont™ Neoprene W family vulcanizates have good resistance to heat aging and compression set—substantially better than vulcanizates of Neoprene GNA or GRT. If properly compounded with nonstaining compounding ingredients, they can be used in applications where staining of finishes cannot be tolerated.

When to Use W Types Neoprene W types are chosen primarily where service conditions call for Neoprene types with the best available heat and compression set resistance. Even when these properties are not the primary consideration, Neoprene W types are frequently used because of their combination of excellent storage stability, uniform processability, broad compounding latitude, and all-around good vulcanizate properties.

DuPont™ Neoprene W M1, W, WHV 100, and WHV Description Neoprene W M1, W, WHV 100, and WHV are nonstaining, general-purpose polychloroprenes. The four grades differ only in Mooney viscosity.

Processing and Performance Features Broad Compounding Latitude

The wide range of viscosity available with these polymers makes it possible to accommodate virtually any desired loading of fillers and plasticizers while still maintaining workable compound viscosity. Because cure accelerators must be used with these types to achieve practical cure rates, processing and cure rate can be varied to suit processing requirements.

Optimum Heat and Compression Set Resistance

Neoprene W compounds provide the best resistance to heat aging and lowest compression set of any Neoprene compound type.

DuPont™ Neoprene WRT and WD Description Neoprene WRT and WD are nonstaining, crystallization-resistant copolymers of chloroprene and 2,3-dichloro-1,3-butadiene. The two types differ only in Mooney viscosity.

Processing and Performance Features Superior Low-Temperature Properties

Neoprene WRT and WD are designed for use in finished products that must remain flexible for long periods at low temperatures. The excellent crystallization resistance of these types helps counteract the increase in rate of crystallization-induced stiffening that is caused by ester plasticizers. Therefore, higher levels of ester plasticizers can be tolerated for increased resistance to thermal stiffening.

Broad Compounding Latitude

The availability of two viscosity grades in these crystallization-resistant polymers makes it possible to accommodate considerable variation in filler and plasticizer loading while still maintaining workable compound viscosity. Because cure accelerators must be used with these types to achieve practical cure rates, processing safety and cure rates can be varied to suit processing requirements. Slightly greater amounts of accelerators are required with Neoprene WRT and WD to achieve cure rates comparable to those of Neoprene W and WHV.

DuPont™ Neoprene WB Description Neoprene WB is a nonstaining polychloroprene that contains a high percentage of gel polymer for superior processibility.

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Processing and Performance Features Outstanding Processing Characteristics

DuPont™ Neoprene WB contains a high percentage of gel polymer. The presence of gel improves processability and Neoprene WB exhibits better processing characteristics than any other type of Neoprene. Compounds based on Neoprene WB are firm and have very low nerve. They are fast-extruding, yielding smooth extrudates with good collapse resistance, sharp die definition, and low die swell. They also calender well, yielding smooth sheets with low shrinkage.

Reduced Vulcanizate Strength Vulcanizates of Neoprene WB exhibit good resistance to heat aging and compression set that is typical of the Neoprene W types. However, because of higher gel content, vulcanizates of Neoprene WB generally exhibit somewhat lower tensile strength, elongation, tear strength, and resistance to flex cut growth than vulcanizates of Neoprene W.

For this reason, Neoprene WB is most often used in blends with other types of Neoprene to improve processing at minimum sacrifice in vulcanizate strength.

The DuPont™ Neoprene T Types General Characteristics The chemical composition and performance characteristics of Neoprene T type products are similar to those of Neoprene W types. The T types are copolymers of chloroprene and a gel-forming comonomer. They do not contain elemental sulfur, other curatives, or additives that can decompose into a curative. They do not contain staining stabilizers, and they have more uniform molecular weight distribution than the G types. They have excellent raw polymer storage stability — similar to that of W types and better than that of G types.

Because of the comonomer used, all Neoprene T types contain a component that is a highly crosslinked gel form of polychloroprene, similar to that contained in Neoprene WB, which acts as an internal processing aid. As a result, the T types are generally better processing than W types (except Neoprene WB). They offer smooth, fast extrusion and calendering with little or no loss in physical properties.

Processing Characteristics The choice of Neoprene T types over blends of Neoprene WB with other types is usually made on the basis that a single polymer will generally mix more uniformly and give less batch-to-batch variability in processing and properties than a physical blend of two polymers.

Neoprene T types are similar to W types in that molecular weight does not decrease under mechanical shear or by chemical peptization. However, some reduction in viscosity may occur under high shear conditions. The degree of softening is greater for a higher molecular weight polymer such as Neoprene TW-100. Neoprene T type compounds mix relatively quickly with little batch-to-batch variation in compound viscosity. Neoprene T types develop more heat history during mixing and are less sticky than those based on Neoprene GNA and GRT.

Because T types contain gel polymer, the compounds often exhibit improved processing compared to similarly loaded compounds of the corresponding W types—particularly in extrusion and calendering. Manufacturing experience has demonstrated that the extrusion rate can be increased 10– 60%, die swell is less, die definition is sharper, and hollow extrudates resist collapse better when the correct Neoprene T type is substituted for W types (except blends with Neoprene WB). Similarly, calender compounds have less nerve, and therefore less shrinkage; films are smoother and calender speeds can be increased significantly. Green strength is also increased with the use of T types.

Until the introduction of Neoprene T types, fast and smooth processing was achieved by blending W or G types with Neoprene WB; however, some loss in physical properties occurred. Neoprene T types provide improved processibility with little or no sacrifice in properties.

Cure accelerators must be added to T type formulations to achieve practical cure rates and acceptable vulcanizate properties. Considerable latitude in processing safety and cure rate is possible with the T types through selection of the type and amount of curative. Storage stability of mixed Neoprene compounds can be maximized by withholding the accelerator until just prior to final finishing. In addition to accelerators, the materials most likely to impair storage stability are antioxidants and antiozonants. Before accelerators are added to the mix, Neoprene T compounds are much less susceptible to scorch due to heat history than are compounds based on Neoprene G types.

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Curing and Vulcanizate Properties Despite the gel content of DuPont™ Neoprene T types, the mechanical properties of Neoprene T vulcanizates do not differ substantially from those of vulcanizates of the W types. Neoprene T types also provide good resistance to heat aging and compression set that is also a characteristic of DuPont™ Neoprene W types. If properly compounded with nonstaining compounding ingredients, T types can be used in applications where staining of finishes cannot be tolerated.

When to Use T Types Neoprene T types are typically used in calendering and extrusion applications. They are frequently used in the production of extruded profiles requiring low die swell, little distortion, and high green strength. They are useful when properties similar to those of Neoprene W types are needed, coupled with superior processing characteristics.

DuPont™Neoprene TW is an excellent base polymer for extruded products, providing high extrusion speed, low die swell, excellent definition, and very good collapse resistance. In calendered goods, Neoprene TW produces smooth sheeting with low nerve and shrinkage. Neoprene TW-100 offers these same benefits in a higher viscosity range suitable for more heavily loaded compounds.

Handling Precautions DuPont is not aware of any unusual health hazards associated with any Neoprene solid polymer. However, for all the solid polymers, routine industrial hygiene practices are recommended during handling and processing to avoid such conditions as dust buildup or static charges. For additional information consult “Guide for Safe Handling and FDA Status of Neoprene Solid Polymers,” and observe the precautions described.

Compounding ingredients used with Neoprene to prepare finished products may present hazards in handling and use. Before proceeding with any compounding work, consult and follow label directions and handling precautions from suppliers of all ingredients. Also, see comments on specific compounding ingredients in the safe handling bulletin.

Information on European Union Dangerous Preparations Directive 1999/45/EC related to Colophony Skin Sensitization Colophony is classified as a skin contact sensitizer under European Union Dangerous Preparations Directive 1999/45/EC effective July 30, 2002. This Directive requires labeling of products that contain colophony at levels equal to or greater than 0.1% (refer to the Directives for specific details). Solid (dry type) Neoprene adhesive grade products manufactured by DuPont contain about 4% colophony (CAS No. 8050-09-7). Toxicological tests have demonstrated that dry Neoprene is not a skin sensitizer. Because of this testing, dry Neoprene polymer is not subject to mandatory labeling under the above Directive despite the presence of colophony. However, when these Neoprene adhesive grade products are dissolved in organic solvents, colophony may still be present at concentrations up to 0.8% depending on the solids content of the solutions. In the absence of data showing the adhesive is not a skin sensitizer, the adhesive could be subject to the above EU regulation.

We recommend that manufacturers and marketers of adhesive solutions containing DuPont™ Neoprene (dry type) adhesive grade products determine whether the colophony level is above 0.1%. If the manufactured preparation has a colophony content of less than 0.1% it will not be subject to mandatory labeling (provided no other constituents necessitate mandatory labeling). Manufactured preparations that contain higher colophony contents will require the labeling and/or container notices described in the Directive.

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The information set forth herein is furnished free of charge and is based on technical data that DuPont believes to be reliable and falls within the normal range of properties. It is intended for use by persons having technical skill, at their own discretion and risk. This data should not be used to establish specification limits nor used alone as the basis of design. Handling precaution information is given with the understanding that those using it will satisfy themselves that their particular conditions of use present no health or safety hazards. Since conditions of product use and disposal are outside our control, we make no warranties, express or implied, and assume no liability in connection with any use of this information. As with any product, evaluation under end-use conditions prior to specification is essential. Nothing herein is to be taken as a license to operate or a recommendation to infringe on patents.

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(01/04) Reference No. NPE-H68563-00-K0910