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AMI Brings together Experts to Discuss Changes to PVC Formulations

PVC recipes are currently evolving to take into account legislation against the use of heavy metal stabilisers worldwide, trends in flame retardants and the controversies over the use of some phthalate plasticisers. AMI brought together some of the top experts in this field to a global conference on PVC Formulation, which took place in Cologne in March 2010.

Jon Nash of AMI Consulting reviewed the market trends. World demand for PVC amounted to around 33 million tonnes in 2009, with a fall in demand in NAFTA, Europe and Japan. Overall, there was a drop of 1-2% in 2009, compared with a fall of 6-7% in 2008. Growth was seen in India and Asia, and is expected to continue in these regions and in Latin America in the foreseeable future. Construction markets in developing countries are driving much of this increase in applications such as pipe, cable and profile. Most compounding is carried out in house, with only around 25% bought in across Europe in 2009.

Shin-Etsu PVC has examined the effects of replacing lead stabilisers on PVC pipes and profiles in work with Rehau and Dow. In the case of Ca/Zn stabilisers, the comments from customers were that they needed co-stabilisers, different lubrication packages, experienced more plate-out and required changes to processing conditions. The lead stabilisers outperformed Ca/Zn in tests such as creep although ageing improved this. Gelation levels were higher in Ca/Zn stabilised pipes compared to lead and this was affected by the lubricant package. This work demonstrates the need to look at the whole formulation when one ingredient is replaced, and at the performance of the end product. Sud-Chemie has synthetic hydrotalcite co-stabilisers for Ca/Zn systems, with major investments in production capacity from 2007 onwards to safeguard growing demand. In 2009, 30% of stabiliser production in the EU was lead-based, with 52% Ca/Zn and around 8% tin-based (total 133,500 tons). This compares to 38% lead and 44% Ca/Zn in 2008. This trend is expected to continue as lead is phased out completely in 2013.

Tin stabilisers are used across the EU, with the highest use in calendered film (10,000 tons) and sheet and profile (1,500 tons), according to the European Stabilisers Producers Association. REACH is affecting this market segment, particularly where compounds are rated as having potential to be carcinogenic, mutagenic or toxic to reproduction (CMR). Dibutyl tins have Reprotoxic Category 2 and Mutagenic Category 3 and will be restricted within 3 years, with an exemption to January 2015 for use in soft PVC profiles, coated fabrics for outdoor use, outdoor pipes and roofing materials. Dioctyl tins will be restricted after January 2012 in skin contact textiles, wall and floor coverings. The association has published information to assist companies to work out the implications of the legislation.

PVC stabilisers need to act as HCl scavengers, remove or replace labile chloride ions, react with free radicals (antioxidant), and modify the polyene to retard colour development, chain scission and crosslinking. According to Arkema, mono octyl tin stabilisers offer excellent transparency with almost no discoloration, for applications like film. This product is now available commercially as Thermolite 895. It has been tested in calendering of rigid PVC.

The conversion from lead to Ca/Zn stabilisers in window profiles has been studied by Baerlocher. The new product is less dense than the lead equivalent, which means there is a reduction of non meltable components in the formulation and the filler load can be increased. Lubricant systems have to be changed, volatile additives should be reduced and the formulation examined to prevent cross reactions. For example, common Ca/Zn systems need beta-diketones which can split off acetyl acetone, which in turn can react with iron ions to give a reddish deposit in the degassing zone. This can be reduced by optimising the dose of diketone or substituting it (this is under development). The Turkish company, Akdeniz Kimya, produces Ca/Zn stabilisers and has been looking at the whole formulation for profiles, with particular attention to the lubricant pack. The company has a new low zinc product, which it says leads to high gloss and low plate out.

Catena Additives cultivates a "green" image in its products and is making tin stabiliser replacements and non-halogenated flame retardants. It is part of the Floridienne Group. The Eurostab stabiliser contains no solvent and is suitable for rigid transparent applications, such as sheet for construction and advertising boards. It offers good weatherability compared to tin compounds. A new product was introduced at the AMI conference: the Safire group of flame retardants comprises nitrogen and phosphorus containing polymer compounds. Catena Additives has carried out research to develop formulations for cable, using a Metrastat Gear Oven to test for thermal stability. In combination with aluminium trihydrate (ATH), thermal stability and mechanical properties were improved using Safire additives. These materials are patented and undergoing the ELINCS process.

Chemtura formed a new vinyl additives company in 2010. It supplies a range of mixed metal, tin and organic stabilisers, as well as liquid phosphate esters, impact modifiers, antistatic agents and lubricants. The company offers the "green" product epoxidized soya bean oil, to improve the heat stability of metal soaps and organic systems. This product also acts as an internal lubricant or processing aid. Chemtura has worked on replacement products affected by legislation and carried out testing: for example, its organic based stabiliser has excellent transparency and is effective in flooring top coat, guarding against yellowing or amine staining (pinking); and the formulation passes the VDA criteria for fogging in automotive foils.

Functional fillers are used in PVC compounds in stabilization, flame retardancy and smoke suppression. Nabaltec has tested a range of mineral hydrates for their effects. Boehmite (aluminium oxide hydrate) was found to be an alternative flame retardant to ATH, giving high tensile strength and low water uptake. Calcium-aluminium-hydrate-carbonate (CAHC) works with ATH, it is an acid scavenger and co-stabiliser; the combination reduces the smoke release rate. Zinc borate with ATH reduces smoke, but reduces thermal stability and cuts the time to ignition. Zinc borate can be combined with CAHC to improve flame retardancy and thermal performance of PVC.

There are new developments in plasticisers. Roquette Freres operates a biorefinery in France. It is producing isosorbide di-esters as sustainable plasticisers by esterification of isosorbide (produced by dehydration of sorbitol) using vegetable based fatty acids. It is being tested in industrial trials in PVC products such as flooring, sun shades, sealing and conveyors.

Polymeric plasticisers have been developed by Lanxess Deutschland from adipic acid polyesters (polyadipates). Polymeric plasticisers have low volatility, migration and extractability. Applications include film, cling film (food contact), hose, cables, shoes and clothing. The company has produced a variety of viscosities in the Ultramoll range and tested them in formulations, for example in extraction with olive oil. Ultramoll IV is medium viscosity to improve processing, has Food Contact Listing in the EU and is in compliance with the US FDA 21 CFR.

Eastman is also in the market with new high solvating plasticisers for PVC plastisols. Dioctyl terephthalate (DOTP) has been on the market since 1975 and is used at around 28 phr in plastisols: it is not adversely listed and is commercially available as Eastman 168. It is going through REACH registration for 2010. New chemicals are being tested such as dibutyl terephthalate (DBT), di-isobutyl phthalate and benzoate esters. DBT is being supported for REACH for sensitive applications. Both DOTP and DBT are "label-free and readily biodegradable for EU markets".

There are a variety of lubricants available. Clariant Produkte (Deutschland) has tested several classes including hydrocarbon/polyolefin wax, oxidised polyolefin and ester wax for pipe, profile and film formulations with Ca/Zn stabilisers. Combinations of waxes can improve performance significantly, lowering energy consumption and leading to higher output in production. For example, the best combination for profiles was found to be oxidised PE wax + PE wax + internal esters + montanic acid ester.

Impurities in calcium carbonate can cause problems. Chemson has examined a series of mineral samples to look at the effects, examining levels of iron oxide, manganese oxide, aluminium oxide. Iron has the biggest adverse effect on colour and colour hold. Manganese does not affect initial colour, but does affect colour hold. Titanium dioxide is added to PVC as an UV absorber, opacifier (especially rutile), and hides the yellowing of PVC that results from processing and weathering. DuPont Titanium Technologies is the largest producer and has studied these effects in depth.

The Shepherd Color Co. Has developed infrared reflective pigments to reduce heat build-up on darker colours. Complex inorganic coloured pigments are chemical resistant, have good processing properties and weatherability. The company has been running weathering tests for three decades in South Florida on colours like spinel black, titanate yellow and cobalt green. When infrared light is reflected the thermal heat exposure of the material is reduced, and as IR light constitutes 50% of solar radiation this is very significant. The visible light is still absorbed thus maintaining the appearance of the colour. Total solar reflectance is measured using ASTM E903-96. Rapid Optical Control (ROC) has new processing technology for compounding, which carries out colour measurements by automatic sampling and gives results in 3 minutes, leading to faster colour correction and improved quality.

Buss is a leading expert in compounding equipment. It has developed an oscillating screw kneader for highly filled PVC, i.e. compounds with over 35% volume fraction of filler. The advantage is cost, as calcium carbonate costs less than PVC resin. The challenge is to break open the agglomerates of particles, surface wet them, and remove air and volatiles. The screw functions in four sections: intake of dry blend and extra filler, melt and mix, second intake section with hot fed calcium carbonate, and the final homogenization zone. As one example, rigid PVC for window sills was extruded at over 110 phr filler, at 2600-3900 kg/h.

The AMI conference on PVC formulation attracted a record number of delegates in 2010, and the event was a great success, providing a forum to debate the complexities of formulating PVC in the new millennium.

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