AMI’s 3rd annual international conference on PVC compounding was held in February 2011 in Dusseldorf, Germany to debate the latest innovations in vinyl additives and recipes. Jon Nash, Consultant at Applied Market Information, gave an overview of the recovery in the global markets: current demand is running at 34.5 mln tons, which is still below the 2007 level. The mature markets of NAFTA and Europe are offset against the developing markets, giving an average annual growth rate of 4% from 2010-2014, with demand in China predicted to rise fastest at 8-10% pa. World production capacity is around 44 mln tons. In Europe around 85% of compounding is in house for applications such as pipe, film, sheet and flooring. The biggest EU market for bought-in compounds amounted to 21% for the cable industry, followed by 16% for window profile manufacturing.
Changes to European chemical regulations are driving research into new PVC formulations, particularly heavy metal stabiliser replacements. Ineos Compounds is looking at replacement recipes after the phase out of dibutyl tin, which is affected by EU Directive 2009/425/EC. Dibutyl tin compounds are good heat and light stabilisers and give good clarity facilitating the production of coloured profiles and fittings, whereas the alternative materials all have disadvantages including the octyl tins, calcium-zinc and organic stabilisers. The company studied the problems by application, for example formulations for gamma irradiation-stable medical moulding have been developed using a stabiliser based on octyl tin mercaptide. Catena Additives has been developing clear, rigid profile compounds based around a new Ca/Zn stabiliser. There were interactions with the impact modifier in the original tin-based recipe and two alternatives were examined: methacrylate-acrylonitrile-butadiene-styrene (MABS) and methacrylate-butadiene-styrene (MBS). The results gave a material with comparable IZOD impact performance to tin-stabilised materials, for applications such as corrugated sheet.
Chemson has new calcium-zinc stearate stabilisers and has been testing different ratios and fused products in formulations with SolVin PVC, filler, titanium dioxide and impact modifier (as for window profiles). Kalpataru Organics is a leading supplier of PVC stabilisers in India, with a product range including Ca/Zn and Ba/Zn, as well as traditional lead – tin and lead prices have been rising and this is driving the regional market towards alternative chemicals. The company’s Ca/Zn solid stabiliser systems include hydrotalcites, zeolites, antioxidants, polyols and lubricants, each with a different role. For example, hydrotalcites contribute to both static thermal stability and electrical properties. Akdeniz Kimya, based in Turkey, supplies low zinc stabilisers for pipe and profile, and organic stabiliser systems.
Kisuma Chemicals is part of the Kyowa Group which was the first company in the world to synthesise hydrotalcites, one example is Al2Mg4(OH)12(CO3).nH2O. This chemical acts as a stabiliser in the autocatalytic dehydrohalogenation process by immobilising the chloride ions. It is usually coated with a fatty acid for optimal dispersion in PVC. The Kuraray Group produces polyvinyl alcohol (PVOH), which can be used as a co-stabiliser with Ca/Zn systems improving thermal stability in lead-free PVC compounds. Dispersion is important and this depends on the processing temperature, lubricants and the particle size of the PVOH.
Minerals are used for a variety of functions in PVC compounds. The calcined kaolins from Burgess Pigments are used in electrical insulation materials approved by Underwriters Laboratories (UL). The kaolin is fired or calcined to remove waters of hydration. A typical UL THWN PVC formulation includes K=70 PVC resin, TINTM and DTDP plasticisers, Ca/Zn stabiliser, stearate lubricant, antimony trioxide, Omya calcium carbonate and calcined kaolin.
Lubricants are an essential part of PVC formulations. Clariant Produkte (Deutschland) recently compared the performance of high molecular weight Fischer Tropsch paraffins, metallocene PE and PP and conventional PE waxes in two different types of pipe compounds, Ca-Zn stabilised and organic-based stabilised (OBS). These lubricants are non-polar and therefore incompatible with PVC, so the formulation is a balancing act. For each compound type, the best results were achieved with a combination of lubricants.
Phosphate esters from Lanxess are used as flame retardants in flexible PVC. They act by decomposing under heat to phosphoric acid, which forms a protective char layer. There are several types, aryl, aryl-alkyl, alkyl and chlorinated, and they can also function as plasticisers and viscosity modifiers.
The construction market is looking for innovative decorative effects, which can be achieved by colouring PVC-u. There are several types of colour preparation available involving dye and pigment in a range of formats including masterbatch (using a carrier resin), dye packs (blends), liquid colours (liquid base), and wax dispersions. Colour Tone Masterbatch supplies concentrates to this market, giving compounders the opportunity to control colour in-house. As with all PVC recipes, the balance of additives has to be adjusted. The Vynacol range includes inorganic pigments at up to 70% and organic pigments at up to 40% and packages are tailored for different applications, looking at factors such as weatherability, resistance to chalking, thermal stability and acid resistance.
There is a continuing debate about the safety of phthalate plasticisers, which is driving development of other types. Eastman has alternatives for plastisol applications including di-octyl terephthalate (DOTP), which is a general purpose plasticiser suitable as a replacement for DEHP or DINP. The company’s DBT (di-butyl terephthalate) and Benzoflex® dibenzoate are high solvating specialty plasticisers, used in replacement of DBP, DIBP and BBP. Danisco is focusing on bio-based chemical production including PVC plasticisers from a variety of plant oils. Soft-n-safe is acetylated monoglyceride (castor) and 95CO is acetylated monoglyceride (coconut C12-16). Glycerol triacetate (triacetin) is the latest offering from Lanxess Deutschland, it is currently used as a plasticiser in applications such as chewing gum, food flavourings and cellulose-based plastics. It does not function as a primary plasticiser for PVC but can be used in combination with plasticisers, with the benefit of reducing viscosity in plastisols and accelerating the fusion behaviour of standard plasticisers.
In the change from lead stabilisers there has been a reduction in the softening point of PVC, which can be addressed by blending in high transition temperature styrenic polymers such as ASA and high heat (HH) ABS. BASF Styrenic became Styrolution on 1st January 2011 and is in a joint venture with Ineos: Styrolution supplies this market.
The PVC compounding process involves a wide range of equipment from bag emptying machinery to silos for PVC and fillers, additive weighing and dosing stations, through to the mixer. K-tron supplies equipment for feeding and conveying additives including mineral fillers. There are a lot of factors to consider for each additive, such as humidity, temperature, vibration, inter-particle forces (van der Waals, electrostatic), and friction between the material and the conveyor. At the other end of the process, Coperion supplies mixers, and pellet making machinery which has been tested for PVC-based wood-plastic composites along with general PVC compounds.
The annual AMI PVC Formulation conference provides a global discussion forum for the vinyl industry to find the optimum recipes for the dynamic global marketplace. The next conference will be held in March 2012 at Dusseldorf.