|Alternative plasticisers from bio-sources and new stabilisers have been developed in the PVC industry to replace heavy metal materials. As any compounder knows, replacing one ingredient means adjusting the whole balance. Another issue is the supply chain for new materials and it is important to ensure sustainability of supply before embarking on global reformulation. The PVC industry met at AMI�s PVC Formulation 2012 conference to debate the market trends and the latest recipes to improve the environmental performance of vinyl compounds.
VinylPlus is driving many of the environmental initiatives in Europe and reported that in the 27 EU countries around 1 mln tons of post-consumer PVC has been recycled, cadmium stabilisers have been phased out and lead stabilisers are scheduled for complete substitution by 2015. In addition more than 80% of plasticisers are now unclassified high molecular weight phthalates thus addressing many of the concerns that have affected the industry. PVCPlus is campaigning to improve the image of soft PVC.
Dr Josef Ertl, CEO of Vinnolit, has reviewed the business situation in Europe: the PVC market in Western Europe peaked at 6.5 mln tons in 2007 and was just over 5 mln tons in 2011. At the same time the market in Eastern Europe has seen growth in every year since 2005 except 2009 and has now reached around 1.2 mln tons. As for the situation in 2012, Dr Ertl indicated, �Attenuation of the economic recovery has put a damper on PVC demand� and the situation could move in either direction depending on business confidence. In the USA in 2010 nearly 50% of resin was used in extrusion according to the ACC, with 48% going into pipe, 12% into siding, 6% into profiles and 3.5% into fence and decking. Mark Lavach at Arkema has reviewed the formulation trends for rigid PVC in North America. Different sectors are regulated by different bodies, for example there is a code for profiles set by the independent trade association AAMA, which is not taken up by all companies. For exterior PVC products, one issue will always be weathering performance, for siding this includes the colour stability of new darker products. Foamed products with light-weighting are making inroads. Cost is a factor in every sector and foaming reduces material use. At the same time in Europe, Baerlocher estimates the 2010 PVC window profile market to be 2.5 mln tons with Turkey the largest manufacturer at 590 ktons, followed by Germany at 580 ktons and Russia at 443 ktons. The use of stabiliser type varies by region: the EU countries have cut lead (Pb) use to 30% in profiles, compared to 50% in the whole of Europe, 97% in Asia, 80% in South America and 93% in the Middle East, in contrast the USA is 100% tin stabilisers. Calcium-based alternative stabilisers require co-stabilisers to ensure colour hold. The sustainable options for PVC are ethylene feedstocks from bio-sources combined with bio-based plasticisers, impact modifiers and other additives, PolyOne is working on new products and Roger Avakian the Vice-President of Scientific Development has focused on PVC additives. Demands are complex, for example plasticisers are required with low temperature flexibility and high temperature stability. The company has a new bio-based high solvating plasticiser, trade name reFlex 100: the feedstock was developed in cooperation with Archer Daniels Midland and the technology was licensed from Battelle. It can be used to replace butyl benzyl phthalate (BBP) and is being produced on a commercial scale. As a co-plasticiser it is claimed to reduce the gelation and fusion time and to improve heat stability. It has been tested to the USDA Biopreferred standard and contains 94% renewable carbon. The company Segetis is liaising with Arkema to develop another bio-based plasticiser. Segetis has technology to convert cellulosics and sugar to levulinic acid and L-ketals, which can be used to make polyols, polymers and plasticisers. The latter have been tested in flexible PVC and as a co-plasticiser in plastisols. Varteco is also in this marketplace, V-Ziclus is a general purpose plasticiser and offers potential cost reduction of 3-16% compared to DINP. The feedstock is soybean oil, which is generated as a side-product from manufacturing soybean meal as high protein animal feed. In 2010 Argentina exported 4.4 Mtons of this oil and the figure for 2011 is expected to be 5.3 Mtons. The use of ESBO plasticisers is very common in Argentina due to availability and prices. The Catalan Plastic Centre has carried out a series of tests to assess the potential for replacing DOP. The new plasticiser has been tested in commercial resins and Solvay Indupa has compared V-Ziclus with DINP in commercial formulations. Soya bean oil has been used for decades as an internal lubricant in PVC processing. Clariant Produkte (Deutschland) has developed a new soya bean wax (SBW) by enlarging the molecular weight, and removing double bonds and the high volatility component. SBW shows high performance in both internal and external lubricant behaviour in PVC. It has been tested in film and profile formulations.
There are new plasticisers available as dibenzoate blends from Emerald Kalama Chemical. These are high solvators (similar to phthalate performance), compatible, with good fusion characteristics and resistance to oil and solvent extraction. In plastisols the X-20 blend offers good viscosity and very good solvation. Many PVC products are made white using different grades of titanium dioxide, either the rutile or anatase form. These have different undertone variations from bluish to transparent in the ultrafine form, and properties like hydrophobic/hydrophilic, and weatherability. Sachtleben Chemie has studied the effects of using different grades produced using different methods on the performance of PVC compounds. Impurities like iron, chromium and copper lead to yellowing. The ultrafine grades are transparent, block UV and are resistant to weathering. The crystal lattice can be doped with aluminium, zinc or antimony to increase weather resistance by reducing charge mobility. BASF has also examined colour issues in PVC looking at quality and long-term colour retention. The common problems are fading, chalking, darkening and milkiness, which are not necessarily due to the colorant, but due to the wrong combination of additives in the formulation, like using a low performance shading component with a high performance pigment. There are standards, such as ISO 4892-2 Xenon arc lamp and ASTM G 154, which can be used to test the weathering of different formulations. Microbes can affect the coloration of plastics, for example microbial metabolites can cause a pink staining in flexible vinyl sheet. Lonza (formerly Arch Biocides) supplies antimicrobial additives which help to combat this and also contribute to hygiene on polymer surfaces, which is very important in the healthcare and sports sector to combat pathogens like MRSA. The additive must be selected with the right spectrum of activity and cost-effective performance. It is important to get the formulation right, because antimicrobials can accelerate yellowing and be affected by UV light. Lonza offers zinc 2-pyridinethiol-1-oxide (ZPT, zinc OMADINE) and the more UV resistant n-butyl 1,2-benzisothiazolin-3-one (BBIT, Vanquish 100). INEOS Chlorvinyls is the leading registrant for vinyl chloride for European REACH regulations. There has been some confusion over polymers: these are exempt from registration providing that the monomers are registered, and monomers are subject to full dossier requirement. A consortium of 24 vinyl chloride manufacturers, importers and representatives of non-EU entities prepared a registration dossier for vinyl chloride, with ECVM as the administrator. It is up to a user company to establish the REACH status of ingredients. The overall aim is to reduce the use of Substances of Very High Concern (SVHC) and these are listed in Annex XIV. The latter list includes DEHP, DBP and BBP, and the �sunset date� for ending use of these is February 2015 unless Authorisation is granted for continued use. Arkema is lead registrant for DEHP and is seeking Authorisation. Recycled PVC can include some additives that are no longer used by industry such as cadmium compounds.
PVC stabilisers have been affected by changes to regulations and the move from the use of very effective lead-based compounds. Galata Chemicals produces several types of stabiliser including tin, mixed metal and OBS. It has conducted research on optimal formulation including OBS technology for flexible and plastisol applications. Chemson is looking at the use of heavy-metal free OBS stabilisers in Group 1 building applications, which require low VOC, high flame retardancy, high stiffness, high impact resistance, low water absorption and low plate-out during flow. The �green� credentials of PVC improve with the use of OBS: the uracil backbone is derived as a by-product of caffeine separation from coffee beans and the stearate component is derived from palm oil, while the manufacturing is a �cold� process. The OBS stabilisers have been tested in oriented-PVC pipes and in Dincel PVC walls in Australia. Rigid PVC foam is extruded by three primary methods: free-foaming expansion on leaving the die; inward foaming (Celuka) and coextrusion (skin-core). Formulation affects the melt strength, elasticity, viscosity and solubility of the blowing agent, which all affect cell nucleation, density and growth. Dow Chemical is developing processing aids to maximise nucleation and fast stabilise cells, to give foams with small cells and high cell density. SureCel is a high molecular weight acrylic polymer processing aid, which gives faster gelation time due to greater miscibility with PVC.
Reagens has worked on new stabilisation systems and foaming of PVC sheets and profiles. The material must undergo fast fusion in the extruder to activate the blowing agent, have high melt elasticity for good cell structure, and have good long-run properties with minimal plate-out. The base formulation is S-PVC k57-62, high molecular weight processing aid, stearate-coated filler, stabiliser and blowing agent. The common blowing agent is azodicarbonamide (AZDC) and the Celuka process uses this in combination with sodium bicarbonate. Foam formulation with the new calcium, organic stabilisers is complex. Renolit and Loughborough University have looked at improving the toughness of PVC with sub-micron particles of precipitated/synthetic calcium carbonate (PCC). Ultra-fine grades are 50-500nm comparable with primary particles of PVC, which could generate friction and promote shear and fusion. The study showed that PCC promotes fusion and that fine particle sizes improve impact strength. In Hungary, Dr. Kalman Marossy of Borsodchem is studying the potential of PVC nanocomposites to improve mechanical and electrical properties, lower plasticiser migration and lower flammability. The nano-additives tested include calcium carbonate, silicon dioxide, aluminium oxide, layered silica minerals, carbon nanotubes and halloysite.