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In 2011, 70% of ethylene was produced from ethane rather than naphtha an increase of 15-20% from 2007. China also has reserves of shale gas, but they are less accessible so it is developing coal to olefins technology. Europe is seeing a decline in conventional gas reserves, but political and geographic considerations are limiting the exploitation of shale gas. The situation for feedstock for polypropylene is more complex and various routes are being considered including methanol to polypropylene, olefin methathesis and propane dehydrogenation. In future naptha rich crackers in China and Europe will be used to produce more propylene.
Noru Tsalic, Consultant at Applied Market Information, reviewed the impact on the polyolefin markets at the international conference on Polyolefin Additives in Cologne in 2012. Global demand for PE is currently at around 75 million tonnes and is expected to rise to 90 million tonnes by 2015, for PP these figures are currently 55 rising to 67 million tonnes in 2015. There are planned increases in PP production in Russia (Neftkhim/Sibur), Saudi Arabia (Saudi Polymer, Saudi Kayan) and India (Hindustan Petroleum and ONGC).
Reliance Industries is the fourth largest global producer of PP and has recently developed a new high melt strength grade for ease of processing and wider product range. There are several possible routes to high melt strength PP: increase the amount of high molecular weight polymer, broaden the molecular weight distribution (MWD), control the crystalline morphology or incorporate long chain branching and each has advantages and disadvantages. In technology patented by Ajit Mathur, polyfunctional monomers are grafted onto long chains to promote branching. Antioxidants are used to stabilise this PP during reactive extrusion. The new material was tested in automotive thermoforming and showed good sag resistance, processing temperature of around 200C and uniform wall thickness.
The global market for polymer additives is worth around 20 billion Euros, of which 61% are functional additives, 18% are fillers/reinforcements, 15% are pigments and 6% are impact modifiers. Borealis has experimented with minerals and nucleation in PP: there are several forms of PP with different properties, the alpha form offers stiffness and heat resistance, the beta form is tough and the gamma form offers transparency.
There are several nucleating systems on offer. For beta nucleation quinacridone pigments are effective, but do not have food contact approval and give the plastic an orange colour; trisamide is colourless but less reliable; other options include class IIa metals and dicarboxylic acids, which are colourless, efficient and can get food contact approval, but these are not commercially available. Gahleitner has shown that minerals like micro- and nano-calcium carbonate can improve stiffness and impact strength, provided that there is no alpha nucleating effect.