High performance polymers using functionalised polymers are environment friendly and ensure reduced energy consumption | BY Samit Jain |
Functionalised polymers (polyolefins grafted with maleic anhydride/glycidyl methacrylate or other monomers) have been known to act as coupling agents for filled polymer compounds and as compatibiliser for dis-similar polymers. These functional polymers due to their polar characteristics provide the bonding of fillers to the polymer, thereby enhancing their mechanical properties. These engineered polymers are therefore used in a variety of engineering applications.
Such functional polymers are a result of post reactor grafting reactions. They are used in small quantities but as additives they give substantial improvement in properties of the base compound. Base polymers like LDPE, LLDPE, HDPE, PP, EVA and EPDM are functionalised predominantly with maleic anhydride, glycidyl methacrylate, acrylic acid and other functional groups that impart a degree of polarity to the otherwise nonpolar base polymers. The additional chemical groups provide exceptional compatibility, reactivity and adhesion properties to these resins and cause good affinity towards other polar materials leading to their use in compounding, co-extrusion, printing, and lamination.
Maleic anhydride grafted polypropylene act by improving interfacial adhesion between the filler and polymer matrix. Thus, the polar functional groups in these materials, bind with the surface of fillers like calcium carbonate, talc, mica and glass fibers, while the PP backbone mixes well with the matrix polymer. This results in a better dispersion of the filler and enhances the mechanical properties of the compound. Maleated EPDM is an excellent impact modifier for filled PP compositions. Higher filler loadings also become possible. In such cases, Maleated products replace the conventionally used low molecular weight additives like waxes. Halogen Free Flame Retardant (HFFR) compounds for wires and cables are now becoming the trend around the globe because of environmental concerns of conventionally used PVC cables. MAH grafted polyolefins act as a coupling agent between the HFFR (Aluminum Trihydrate and Magnesium Hydroxide) and the base polymer. When compared with silane coupling agents or other grafted polyolefins, MAH grafted functional polymers provide: superior tensile strength and elongation at break of finished compounds, lower gel content, for higher compound performance consistency; and very low water absorption in finished compounds. Maleic anhydride grafted polyethylenes are used for reactive blending with nylon to improve its overall toughness, particularly in the dry state. Polyethylene on its own is not known to blend with nylon but the anhydride groups in maleated products readily react with the amine end groups in nylon, and compatibilise with polyethylene. These products are suitable for unfilled as well as mineral and glass filled nylons. Such nylon alloys have a wide range of applications, like safety helmets, luggage frames, handles and other components, automobile accessories such as motor cycle side boxes, bake and clutch levers, castor wheels, hand tool bodies, equipment housing, fan blades, rifle butts and industrial components.
Maleated polyethylenes are being successfully used by hopper blending with nylon and moulding into small or large components using screw type injection moulding machines which allow adequate mixing. At the nylon processing temperatures, an alloy having good impact properties is formed during the injection moulding process itself. Value can be added to nylon scrap, be it in the form of fibre, film or moulding waste, by using the compatibilising action of grafted polyethylene. The modified product is suitable for injection moulding applications. Recycling of coming led PET/PE film waste, generated in plenty by the packaging industry, is not possible due to the widely different nature of the two polymers. Maleic anhydride grafted EVA can be used for compatibilising the two polymers in such a mixture. Presence of fillers, inks and other additives in the mixture does not affect the process. Packaging demands high barrier films and sheets for long shelf life. Commodity polymers do not provide adequate barriers but have all the other characteristics like low cost, adequate mechanicals, etc. Barrier properties are obtained by co-extruding a middle layer of polymers such as nylon, EVOH, and PVDC. Functionalised polyolefins are co-extruded as bonding layers between the commodity and barrier polymers. Several products have been indigenously produced in India now for the same.
Wood flour/rice husk polymer composites have all the advantages of polymers and have no disadvantages of wood. The compatibilisation action between the filler and the polymer is imparted by the use of maleic anhydride grafted polyolefins. These composites are finding an increasing replacement in the construction industry particularly in landscaping where wood like finish and texture is desired. They provide the benefits of polymers with the feel of wood.
With a focus on creating environment friendly and energy efficient products, replacement of metals and non – environment friendly chemicals is becoming the need of the hour. This is possible by enhancing the properties of polymers with suitable additives. These additives, being not miscible in the polymer require speciality functionalised polymers to compatibilise or couple them to the polymer matrix. It is imperative that the Indian industry also makes a shift towards using such enhanced polymers to replace metals and other energy intensive raw materials like wood. Europe, USA and the developed countries have made a shift to wood plastic composites in the construction industry, HFFR cable compounds in the wire and cable industry and substantial replacement of metals in the automotive industry. India, targeting to get developed, has no option but to reduce its energy consumption by utilising such options instead of conventionally used materials.