Future growth is expected in global demand for PVC, particularly in Asia, India and Latin America according to Jon Nash, Strategic Research Director at Applied Market Information. Construction applications such as pipe and profile have been a major driver. For example, in India the market is now around 1.3 million tonnes of which 60% is used in pipe. Nash was addressing delegates at the March 2009 AMI conference in Germany on PVC Formulation. The largest producers of PVC in Europe are Ineos Vinyls, Solvin, Arkema and Vinnolit. Most end users compound their own material.
Vinyl 2010 has studied the life cycle assessment (ISO 14044) of PVC including additive production and compounding. Durability is a key factor in performance. Among the commitments of industry is a phase out of lead stabilisers by 2015 and an increase in recycling. A comparison of PVC with other materials is available online at: http://ec.europa.eu/environment/waste/studies/pvc/lca_study.htm
The EU anticipated 150,000 pre-registrations of chemicals under REACH. It received 2.75 million pre-registrations for 150,000 substances from 65,000 companies, which put a great strain on the system. Baerlocher has looked at this situation and the effect on industry. The Substance Information Exchange Forum has been set up to check the data for each chemical, and determine and share additional testing required. Around 300 chemicals are used in PVC and about 50% of additives have been pre-registered. Consortia are being developed for materials such as lead stabilisers, zinc salts and organotin stabilisers, which have an early registration deadline. Costs may be prohibitive for some materials.
Traditional stabilisers in PVC are being phased out – cadmium has already been removed in Europe, lead is next, followed by some tin based products. Zinc is classed as a heavy metal and this may put other additives at risk including the more recent Ca/Zn stabilisers. Polymer-Chemie has been examining other formulations for stabilisation, and also for plasticising PVC where phthalates have had a particularly bad press. In another innovation, it has a modifier that can be added to high load calcium carbonate compounds to maintain properties while keeping the cost down.
Chemson has a new organic stabiliser that has been tested in window profiles against Ca/Pb and Ca/Zn formulations. All profiles showed good weathering performance. Catena has stabilisers for filled and clear PVC, which are solvent-free and can be used for applications from automotive to waterproofing. A typical formulation in a plastisol top coat would be 100 parts PVC: 60 parts plasticiser: 2 parts stabiliser.
Perstorp has a range of polyol co-stabilisers, particularly for the new heavy metal-free stabiliser systems: trimethylolpropane (TMP), di-TMP, pentaerythritol and di-pentaerythritol. These are proving effective in current experiments.
Mineral additives can act as effective co-stabilisers, mainly by acid scavenging. Calcium hydroxide offers good long-term heat stability and low cost, but has disadvantages of discoloration and water uptake. Zeolites offer good stability but also have colour and water uptake issues. Hydrotalcites offer much better long-term heat stability, and water uptake is not a problem, however they are more expensive and affect early colour. The calcium aluminium hydroxyl-carbonate (CAHC) from Nabaltec is used in profiles and sheet: the carbonate exchanges for chloride ions and binds it. It shows higher water uptake than hydrotalcite, but has less impact on gel time. With Ca/Zn systems in profile it shows excellent whiteness and good weathering performance.
Noreen Thomas (Loughborough) is involved in hydrotalcite studies. Hydrotalcite comprises layers of magnesium hydroxide and aluminium hydroxide with interlayers of anionic carbonates and bound water. A lower magnesium:aluminium ratio gives more anions and hence more potential for reaction with HCl. As well as interlayer anions reacting with HCl, the hydroxide groups also react to form metal chlorides. Particles need to be below 1 micron and well dispersed to be effective.
Omya has new direct addition technology for calcium carbonate – this has previously been difficult because the mineral separates during pneumatic transport of the PVC dry blend. Now the calcium carbonate can be added via special mixer to the PVC dry blend. Nine customers in Europe are now using this technology.
Titanium dioxide has a role in stabilisation, and DuPont Titanium Technologies has looked at the effect on discoloration and photo-oxidative bleaching. Heat degrades PVC to short polyenes and HCl, with a yellowing effect, these multiple bond chemicals can be photobleached to white via reaction with oxygen. Surface degradation leads to loss of gloss and chalking. Titanium dioxide absorbs UV and can reduce degradation while the colour masks yellowing however, it can also have a photocatalytic effect; non-chalking grades, commonly with a surface coating of silica are particularly effective at reducing photocatalysis and promoting stabilisation. Non-chalking grades are important in coloured profiles and high gloss applications.
Kabelwerk Eupen is looking at the use of nanoclays (montmorillonite) and layered double hydroxide (LDH) as flame retardants in PVC, as an alternative to aluminium trihydrate (ATH) and magnesium dihydroxide (MDH), antimony trioxide, halogenated plasticisers, phosphate esters, triaryl phosphates, molybdates, zinc borate and zinc stannate. Polar polymers such as PVC form nanocomposites more readily: the clay nanocomposites provides some reduction of heat and smoke reduction but thermal stability needs to be improved, LDH nanocomposite offers better performance.
The flexible PVC market in Europe comprises 27% cable, 15% coating, 15% film & sheet, 15% flooring, 7% profiles and the rest is used in a range of applications such as toys. The largest markets for plasticiser are in Asia, as is growth. BASF is one of the major global suppliers; products include DINCH for toys and medical applications, DPHP for good weathering and low fogging, adipates for low temperature coatings and polymeric plasticisers with oil resistance. BASF sees C9 and C10 phthalates as the main plasticisers in future, with strong growth in the non-phthalate market.
Didier Naert is an expert in plasticisers for ExxonMobil. Around 5.5 million tonnes are used each year across the globe. A plasticiser must have good compatibility with PVC, soften the material and have some mobility in the polymer matrix. Phthalates offer the broadest range of performance at the lowest cost. Alternatives include expoxidised oils, citrates, polyesters, terephthalates, aromatic sulfonates, cyclohexanoate diesters, polyol esters, benzoates, trimellitates and dibasic acid esters.
Eastman is focusing on DEHT (di(2-ethylhexyl) terephthalate) as an alternative to the ortho-phthalates – the company produces a range of plasticisers. The company has tested this chemical as a replacement for DEHP and DINP in a variety of processes including rotational moulding and it often provides improved heat stability. It has been pre-registered for REACH.
Doeflex-Vitapol is the largest independent compounder in the UK. Recently the company has launched an anti-microbial PVC compound to help prevent cross infections. It uses sil