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TPO COATED PP FABRICS AND THEIR APPLICATIONS

Dr. Milind Khandwe Technical Director ENTREMONDE POLYECOATERS LTD., Plot No. 29, M.I.D.C. Road 'C', Street No.13, Satpur, NASHIK - 422 007 (INDIA) eplnsk@dataone.in

INTRODUCTION

Olefin polymers are most chemical resistant inert material available in their commercial category for industrial applications. The last era dominated uses of olefin polymer in commodity applications eliminating traditional metals and non metals. The future is poised for domination of thermoplastic polyolefin (TPO) in engineering polymer applications. Among a few converters all over the world, Entremonde has commercialized and patented 1,2 TPO coating on polypropylene fabric (PP). The TPO coated PP fabrics have many advantage over PVC, PU and rubber coated fabrics.

Use of coated fabrics in manufacture of protective covers, storage systems, agriculture coverings and pond linings has a long history. The products mainly categorized as PVC coated fabrics, PU coated fabrics, acrylic polymer coated fabric, wax coated fabrics (canvas) and rubber-coated fabrics. The common usage of coated fabrics are for example (i) Tarpaulins (ii) Vehicle covers or truck tarpaulins (iii) Tents (iv) Agriculture coverings and fumigation sheets (v) Awnings (vi) Canopies, Tents, Covers etc. In all the types of coated fabrics, fabric component impart desired mechanical property, i.e. Breaking strength, tearing strength, bursting strength, dimensional stability etc. There are number of types of yarns used for manufacturing a fabric, they are polyester, nylon (polyamide), cotton, regenerated cellulose etc. There are number of types of processes that are used in manufacturing a fabric, they are weaving, knitting and random laying of fibers to make a non-woven. The mechanical properties desired in coated fabrics are decided by various properties of fabric used viz. weight, type of yarn, structure whether monofilament, multifilament or texturised, twists, polymer material property like crystallinity, chemical and thermal resistance etc. One can choose a fabric material from almost unlimited options

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available for the purpose of coating as per the end usage requirement.

The coating formulations are based on main polymer categories viz. PVC (Polyvinyl Chloride), PE and other Poly olefins, PU (Polyurethane), Acrylics, Rubber (natural or synthetic) and waxes. Cotton fabric coated with wax formulations are called canvas, is a most common and primitive form of coated fabric. With the invention of new materials and their formulations the number of options available are plenty. The most common are PVC and rubber based formulation where a number of additives are used to prepare a suitable fluid to coat on a fabric. The categories of additives are – fillers, pigments and dyes, solvents, plasticizers and functional additives are used in almost all types of polymers to formulate a compound having desired property. The coatings impart or modify surface properties, barrier and aesthetics of a coated fabric for the required function or end use.

There are number of processes used for coating a fabric but the main categories are two (i) Solution coating including plastisols in the case of PVC (ii) Hot melt coating viz. calendar coating including cold calendaring in the case of rubbers. These processes are generally followed by heating or cooling. The process of coating can be used on one or both the sides of fabric. Surface properties of the coatings can further be modified using physical treatment like embossing, chemical treatment like lacquering, printing, metallizing or film or foil lamination.

There are number of ways to fabricate an article out of coated fabric for protective cover application. Since individual application demand specific size and shape whereas coated fabrics are manufactured in standard width and lengths, depending on the process of manufacturing joining two or more pieces are required. The standard processes are joining with adhesives, stitching, heat welding, HF/RF welding etc. Use of fixtures of desired shape or size viz. eyelets, grommets, D rings, brackets, webbings, ropes are known and are quite common.

The biggest problem is, disposal of waste, generated after the use of coated fabrics. Recycling of coated fabrics is not an easy or a common task. In almost all of the cases the family of the polymer used in manufacturing a fiber and coating compound are heterogeneous hence their physical mixing to regenerate in the form of recyclable goods, is not possible even by applying high

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temperature or pressure. The second option, though not environment friendly remain to dissolve, but again common solvent or mixture of solvents cannot dissolve entire coated fabric for recycling purpose. There are solvents available to partly dissolve a coating but it is not an economical and environmentally friendly process, because of volatility of solvents. The only option remains is to safely incinerate the waste, which has long-term economic effects, if all the precautions are taken from environmental point of view.

Defining ‘thermoplastic polyolefin” (TPO) is difficult3. “Thermoplastic” is a generic term in polymer science; it encompasses a class of polymers that, as mentioned above, soften when heated in a reversible process. The term “olefin” is even more generic being an old chemical name for any molecule containing carbon-carbon double bonds (the modern name for this family of molecules is alkenes). Any polymer formed by chemically linking up many olefin molecules is termed “polyolefin.” According to the latest draft ASTM standard for TPOs, the composition is very non-specific. The standard states that TPOs must contain more than 95% by mass of TPO polymer. The polymer itself is not defined within the standard, which states only that the sheet shall contain the “appropriate” polymers. Because of this loose definition, there is an endless list of chemicals that would fall under this standard (e.g. polyethylene, polypropylene, and isobutylene, as well as their derivatives). Ideally, manufacturers would specify the exact polymer in terms of marketing and labeling. One point is clear, however: unlike plasticized thermoplastics, TPOs do not contain plasticizers. Therefore, the problem of plasticizer loss associated with some plasticized polymers is eliminated.

The product described in the present paper are composites of PP fabrics coated / laminated with thermoplastic polyolefin elastomer which is a special grade of TPO compound made out of reactor modified elastomeric thermoplastic polyolefin.

The TPO and PP are basically inert towards chemical and microorganism attack. The finished products have good resistance towards oxygen and ozone and are flexible at very low temperature i.e. -60ºC. The products are odourless and do not give out toxic gases on burning.

The product are lighter than PU or PVC or rubber coated

fabrics since polyolefin are lower in density than PU, PVC or rubbers formulations. The coating as well as fabric are homologous polymers

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hence are melt recyclable, which is not possible in the case of conventional polymer coated fabrics.

The coated fabrics are available in variety of colors. The dope dyed PP yarn can be produced in excellent uniform bright colors, which are UV stable. TPO coating contains light stable pigments. The properties can be custom designed by altering thickness, strength, flexibility, colors and grain design. In few special cases fire retardancy can also be archived.

The fabrics are available in both side as well as one side coated versions, weldable by thermo fusion welding machine. The fabrics are suitable in a number of applications. To name a few there are:

- Flexible storage tanks for liquids. - High altitude Tents and light weight sport field covers. - Roofing membranes - Ground sheets, agriculture covers and pond lines for algae

farming - Biogas generator covers. - Lightweight swimming pool covers. - Awnings and canopies. - Automobile interiors.

TYPICAL PROPERTIES OF TPO COATED PP FABRICS Properties Test Standards Typical Range

Total Weight (gm/m2) IS: 7016 Pt-I 120 to 350

Total Thickness (mm) IS: 7016 Pt-I 0.15 to 0.75

Breaking strength in kg (Warp & Weft)

IS: 7016 Pt-II 75 to 165

Tearing strength in kg (Warp & Weft)

BS: 3424 7A 5 to 65

Temperature Resistance IS: 7016 Pt-X Up to - 60 Deg.C

Water proofness IS: 7016 Pt-VII Passes

Resistance to Flex IS: 7016 Pt-IV No Cracking

Fungus resistance AATCC Method 30,

1998

Passes

Weather resistance - Good

Hydrolysis resistance - Good

Resistance to UV - Good

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PROCESSING:

The methods of processing are common to processing of coated textiles. As it is understood that the Olefin polymers cannot be coated by conventional spreader knife technique, the extrusion calendering is the best suitable technique used in processing of these materials.

In principle it is basically a continuous extrusion unit consisting of different arrangement of rollers adjustable to a fixed nip opening. The coated fabric is produced by “in situ” pressure laminating the calendered sheet. In this process the care is taken to avoid thermal shocks to the sensitive materials to avoid deterioration of mechanical properties. It is worth mentioning here that the whole system is olefin polymer based and sensitive to the processing temperature. A PP fabric if processed under warp tension at temperature above its Tm

the tenacity is greatly affected. Calendering processes have advantage in terms of uniformity and flawlessness of coating however the initial investment cost is high. Following are description of common calendering process used for TPO coating.

Inverted L calender - These calenders have additional rolls to resurface the TPO sheet before lamination. In this process four rolls provide three metering stations (nips)

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Inclined Z calender - This is typical equipment is used in processing rubbers; an elastomeric TPO can easily be processed with this type of arrangement.

The calender equipments producing coated fabrics are further equipped with Auxiliary equipments which impart processing ease for further handling of material. The auxiliaries are very important for processing of TPO coated PP fabrics.

The fabric pretreatments, formulation of TPO compound with functional additives both processability point of view as well as enhancement of final product properties are few other important parameters considered for processing of these specialty fabrics. A typical calendar coating line is shown in the following figure.

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APPLICATIONS OF TPO COATED PP FABRICS

The TPO coated membranes with various textiles have become headline products for many applications. The textiles i.e. scrims of polyester, polyamide are most popular but used for PP textile is relatively new.

The TPO based products often marketed as “PVC free”, “halide free”, “Green product” to show benefits over rubber and PVC coated fabric.

The other slogan is “heat resistance like EPDM and weldability like PVC” also describes benefits of these products in various applications.

Following described are some specific applications of the TPO coated PP fabrics GROUND SHEET

Ground Sheet is an essential item used by all soldiers in ground forces. This is an item of their personal kit. The Ground Sheet are used as sleeping mat, temporary shelters, to collect water from stream in remote area or as a hammock. The conventional products are rubber, canvas or cotton based, and have inherent problems since natural products are susceptible to degradation in many ways. Cotton fabric being a natural fiber has many disadvantages, like rough use and daily use makes it very vulnerable to microbial attack, when it is wet it does not dry up as quickly as polypropylene. The rubber compound degrades because of unsaturated sites available in its structure. The problem of oozing is quite common in rubber-coated fabrics. Therefore in older version of ground sheets, which is a composite of rubber and cotton, there were many problems, like weathering, UV resistance, and chemical and microbiological resistance and heaviness due to high-density of materials.

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Entremonde Polyecoaters has invented patented1 technology to

manufacture PP- TPO Ground Sheet composite product to over come the above problem faced in conventional product. These Ground Sheets are successfully introduced in our Defence forces. BIO GAS COVERS

The biogas generators have seen traditional covers made out of MS to PVC coated fabric. The biogas is a combination of hydrocarbon fuel gases with some amount of by-product like oxides or sulphur and nitrogen. The waste mass and fermented slurry also contain dissolved gases and microorganism, which are corrosive in nature. The corrosive environment of these generators phased out MS and replaced with PVC coated polyester fabric. The cover made out of PVC coated fabric also experienced short lifetime due to plasticizer migration and inherent poor, chemical and microorganism resistance. PVC coated fabric based products face problem of constant repairs and replacement in a duration of 3 years maximum. The leakage losses are quite high and add negatively to the overall economics of running the generators.

The PP coated TPO fabric is a single solution to all the above cited problems. A typical example of product suitable for the above applications is 1.1mm thick double side TPO coated PP fabric with approximate strength of 135/110 Kg. The compound used for coating is a formulation based on reactor modified TPO instead of traditional TPO blends. The benefit of reactor modified formulation over TPO blends are enormous; it is resistant to UV radiation as well as to corrosive chemicals present in the waste of biogas reactor and the resulting gas, thermally stable i.e. withstanding capacity in the summer heat and winter temperature shocks. The TPO coated PP fabric has been tested at –60ºC. The overall composite is made out of PP homologue hence question of non-compatibility like dissimilar polymers, polyester / Nylon and PVC or PU does not arise. The Specific Gravity remains 0.9 as against 1.3-1.5 of PU or PVC coated Fabric, which is a great handling and operational ease in biogas generator covers.

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The outside color of fabric is light and the inside is made dark to avoid excessive summer heat absorption that could kill anaerobic bacteria. The fabric has all possibilities and flexibility of fabrication like other coated fabrics and also the required maintenance possibilities. The choice of strength, weight and colors remains with the end user requirement as Entremonde has earned expertise in the custom designing of a product. BULK BAGS AND CONTAINER LININGS

Use of olefin polymers in transport worthy packing is very common in consumer as well as in industrial sectors. Fib’s (Flexible intermediate Bulk bags) and BLB’s (Bulk Liner Bags) have gained popularity of transport worthy packing of solids. A very common example is woven sack used in cement and food grain packaging. However FIB’s and BLB’s are produced using TPO coated PP fabrics, sewing or welding them into large bags of required format. In FIB’s one loop, tow loop, four loops etc. are commonly used formats. Welded joints are employed as per the requirement of storage of materials, normally wet resins, fine powders etc. These bags and containers can have valves for ease of filling and unloading. FIB’s and BLB’s offer a cost effective, efficient and environmental friendly way of transporting bulk materials. Use of multiple loops made out of webbing with monofilament PP yarn provides extra strength and thus the bags can be handled using cranes. These can be manufactured and sealed very fast using ultrasonic or heat welding.

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ROOFING MEMBRANES

In typical low slope roofing systems thermal insulation barrier and water proofing membrane determines comfort of home. The traditional membranes consist of PVC or EPDM coated polyester or polyamide fabric. But as discussed earlier PVC and EPDM materials have their own draw back. New concept of TPO coated fabric came out with all possible solution to prevailing drawbacks of conventional materials. Thanks to the developments in multifilament PP yarns, a sufficiently high tensile strength textile can be manufactured for this application. The conventional welding equipment can be used for on the spot welding operations.

FLEXIBLE LIQUID STORAGE TANKS

Flexi tanks are containers made out of coated fabrics in various shapes and sizes. The common shapes are pillow type, onion, orange etc. that ranges from 250 liters to 50,000 liters capacity. These types of tanks provide temporary as well as long term liquid storage facility. They are used in water, oil, fruit juice, milk products, chemical and fuel storage and / or transportation. The flexi tanks are categorized into two types one time used bulk containers and permanent use containers. Traditionally rubber coated, PVC coated or TPU coated fabrics are used in these application. TPO coated PP fabrics have many distinct advantages in terms of inertness of these fabrics to various solvents, these are relatively safe for food grade applications following photographs shows some tanks.

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AUTOMOTIVE INTERIORS

Thermoplastic olefins (TPO) are new generation compounds, which find increasing application in automotive interiors. TPO’s are materials of future and are finding their place due to properties over the existing materials.

At present, PVC is dominantly used in many of the auto interior applications for door panels, roofing upholstery etc. There are certain reasons why PVC is not the preferred interior material abroad any more.

In European markets, there are strong environmental objections to use PVC because of lead and cadmium containing additives, Phthalate plasticisers and lack of recyclability. Besides this, PVC coated fabric suffers from migration properties of the plasticizers leading to fogging and poor ageing problems.

Against this, TPO coated on PP fabric, offers considerable

following advantages.

50,000 liters

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1. Since TPO is made out of polymeric materials and pigments, problems associated with plasticizer migration of PVC are totally eliminated as also cracking problems due to ageing.

2. The light weightness of TPO coated fabric is remarkable. This is primarily due to sp.gravity differences.

3. There is absolutely no smell in the coated fabric unlike in the case of PVC Coated fabrics.

4. The feel is also dry. If offers good cleaning properties. 5. The oil and chemical resistance are superior to those of PVC

Coated fabrics.

The interiors made of TPO coated fabrics have distinct advantage of recycling, as they are same family of materials used in structure and skins etc. Though not a major critical requirement for Indian market but under the globalization norms, this is an implied need of auto interiors. SPORTING TENTS, LIGHT WEIGHT SPORT FIELD COVERS AGRICULTURE COVERINGS AND TRUCK TARPAULINS:

The use of polyolefin polymers especially polypropylene is common in sports and agriculture application4. The artificial grass polypropylene based apparels due to wicking properties, pond lines green house covers are few examples. TPO coated PP fabrics find application in all above-mentioned applications as per their material property benefits as discussed previously over conventional PVC coated fabrics. The PVC coated fabric faces problem due to plasticizer migration and they are not easy to clean. The material used in PVC based product are higher in density, therefore they are quite heavy and difficult to handle. Following photographs illustrate these applications.

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CONCLUSION

The woven-PP TPO coated products are finding diverse application in industry. The demanding application areas are building and construction products where these fabrics find application as house wrap peel and stick wind flashing, under slab vapor retarder. The new application in out door banners, posters, construction sheet, fabric architecture pond liner and geotextiles are developing areas. In conclusion the possible applications of PP TPO composite are limited by once own imagination.

REFERENCES 1. M.Khandwe, A.K. Mody Indian Patent 211228 2. M.Khandwe, A.K. Mody International patent WO 2006/109319 Al. 3. R.M.Paroli et al. www.irc.nrc-cnrc.gc.ca/pubs/cuts/30_e.html 4. http://www.eatp.org