Polymer additives perform a range of functions to enhance the properties of plastics and is a growing industry valued at billions of dollars worldwide. At the most basic level, additives are a way to bulk out a polymer and thereby reduce its cost. However, additives are normally designed to improve at least one specific property, such as flame retardancy – one of the fastest growing segments of the additives markets – or wear resistance.
PVC is the workhorse polymer which consumes a substantial share of additives. Phthalates are used primarily to soften polyvinyl chloride (PVC). Lower-molecular-weight phthalates (3-6 carbon atoms in their backbone) are being gradually replaced in many products in the United States, Canada, and European Union over health concerns, being replaced by high-molecular-weight phthalates (those with more than six carbons in their backbone, which gives them increased permanency and durability). While as recently as 2010, the market was still dominated by high-phthalate plasticizers, due to legal provisions and growing environmental awareness and perceptions, producers are increasingly being forced to use non-phthalate plasticizers.
Polypropylene is a notoriously unstable material which depends on additives to stabilize chemical linkages which without any risk of degradation. Strictly speaking, substances which just provide a suitable medium in which polymerisation occurs or directly influence polymer synthesis are not additives and are called polymerisation aids. Some examples are accelerators, catalysts, catalyst supports, cross-linking agents, initiators and polymerisation inhibitors.
But PP is still the fastest growing market for additives which impart new properties to the base material. Examples are greater clarity, improved organoleptic properties and superior aesthetics, derived from better pigment dispersions.
Away from commodity polymers, additives are used with speciality engineering polymers to enhance properties. A recent example is Solvay’s new wear-resistant Veradel® polyethersulfone, an advanced grade for automotive powertrains. Formulated to replace metal in automotive applications prone to friction and wear.
The injection moldable Veradel® 3300 SL 30 PESU resin is formulated with a ternary anti-friction/anti-wear additive system comprised of carbon fiber, graphite and polytetrafluoroethylene (PTFE). It offers excellent wear resistance to broaden metal replacement options in oil pumps and EGR systems where thermoplastic parts come into contact with metals, such as oil pumps and exhaust gas recirculation (EGR) systems. The new resin exhibits wear resistance and a low coefficient of friction in both dry and lubricated environments. .
Overall, additives are becoming increasingly sophisticated. Some of the drivers are to provide multifunctionality, the need for improved additives for recycled materials, processing of polymer blends, and an increasing interest in so-called “Green Composites” – plastics derived from naturally-occurring materials such as wood and cellulosics. However, despite the push to develop more sophisticated additives, it is difficult to introduce an additive in a material without a rigorous life cycle analysis of the material, to ensure that the additive used is compatible with sustainability and disposal.
The impact on additives of nanoscience and technology is likely to be significant. Nanooxides, nanotalcs and nanocarbon are emerging to derive new properties which are not possible with micron-sized particles. This in turn will need yet more additives to prevent filler agglomeration and manage dispersion of the additive on the so- called nanodimension.
Nano particles are also used to impart special properties into coatings for polymers. Known as Small Molecule Surface Modification (SMSM), it provides a way of enhancing several surface properties of mouldings at the same time. The Nanoparticles used can be surface modified with organic compounds to bestow specific combinations of desired properties: hydrophilic, hydrophobic, adhesive, anti-adhesive, acidic, basic, inert, etc.
Nanoparticles thus modified can be used to develop nanocomposites, which combine the physical solid-state properties of, for example, ceramics or semiconductors, with classic polymer-processing methods. Titanium dioxide, barium titanate, indium-tin oxide or zirconium dioxide are examples of materials used as nanoparticles.
In addition to the intrinsic chemical composition of the nanoparticles and their SMSM surface treatment, the properties that are attainable for the desired coatings also vary with the size and dispersal mode of the nanoparticles.
At the Leibniz Institute for New Materials (INM), situated in Saarbrücken, composite systems are produced via wet-chemical processes. The modified nanoparticles and additives combine with a polymer matrix (an epoxy resin, an acrylate, a polyimide for example) or a hybrid matrix (organic-inorganic) to produce a coatable composite system known as a Nanomer.
“The modular principle makes it possible to achieve a number of properties at one and the same time in one material,” explains Carsten Becker-Willinger, head of the Nanomers programme.
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Dear Sir,
We are working on a project with customer to improve the abrasion and wear resistance of rigid PVC. Besides using a high K value grade of PVC, could you advise are there any additive that can be blended in PVC formulation to enhance the surface wear and abrasion resistance of rigid PVC .
Kindly advise
H T Thai
DuPont Performance Materials