The global market for polyolefins is in transition as the entry of cheap supplies of shale gas in the US is leading to a fall in the price of feedstock for ethylene affecting the supply chain. New ethylene crackers are planned in North America by most major companies including Formosa, Dow, Shell, CP Chem, Sasol, Indorama, SABIC, Braskem and Occidental. 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.
SABIC has been testing PP clay nanocomposites to improve fracture behaviour. First a masterbatch was prepared, and then compounds were prepared with different levels of clay and examined for particle dispersion using X-ray diffraction and electron microscopy. The tensile modulus showed 40% improvement with 3% clay and 50% improvement with 5% clay.
Safety testing is an essential part of testing new materials for sensitive applications like food packaging, water pipes and medical devices. Norner Innovation has looked at the issue of non-intentionally added substances (NIAS) in polyolefins, which are now specifically regulated by the EU and the term denotes impurities, degradation or reaction products. There is a also a new standard for safety of leachables for water contact material (EN 15768, 2012). In the Norner test for NIAS, the polyolefin is mixed with additives and compounded in a twin screw extruder with a nitrogen flush to simulate plant conditions, then extruded several times to simulate processing. A polyethylene was compounded with phosphite and synergistic phenolic antioxidants and tested, using different brands of additive (e.g. Irgafos 168, Songnox 6260 and Sumilizer GP). There were significant differences in the results due to the variation in impurities from each product.
Migration of additives from polymers is an important issue and Tosaf has studied this by examining packaging films. Migrating additives can cause bloom and may affect lamination, printing and sealing. Many factors affect migration including the additive concentration, the environment and the temperature. Some additives are designed to migrate to the surface to impart specific properties like erucamide a slip agent, which reduces adhesion of film to film or to processing equipment. At 60C erucamide becomes more soluble in the polymer, so an additional slip agent can be added which migrates out at this temperature.
Around 27% of all plastics additives and pigments from BASF are used in textiles and agriculture. The global market for PP fibre in 2010 amounted to 6.3 million tonnes and global growth is predicted at 1.5% each year to 2020, with highest rates in the Middle East. BASF has investigated the compound recipes for PP fibre to improve stabilisation and provide better properties for specific applications. The additives include process stabilisers to protect the polymer from breakage and die build-up during spinning with Irgastab FS 533 for higher performance including better tenacity retention in oven testing and UV resistance tested outdoors in Bahrain. There is another range of light stabilisers; the hindered amine stabiliser (HAS) group.
The long-term building and construction market is the target for a new polyolefin stabiliser from Cytec Industries. Areas such as TPO roofing are expected to grow at 3.8% each year in North America with environmentally-friendly roof formats growing fastest along with innovations like tiles. The new Cynergy B877 stabiliser was tested for weathering using LyondellBasell 6301 PP resin exposed to UV: there was superior colour and gloss retention at a lower additive concentration (0.35%). Similar improvements were found with TPO compounds. The new additive has been tested in situ in applications such as pigmented PP siding.
Albemarle has launched a new antioxidant additive with a chemical formula 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (Ethanox 330). Impurities in polyolefins can generate peroxy-radicals and start an autocatalytic oxidation reaction and antioxidants block this. Ethanox 330 is a long-term stabiliser, which has low extractability and good processing stability. It has superior resistance to hydrolysis compared to Irganox 1010 and has been tested for applications such as PE pipe.
Flame retardancy is the focus of Great Lakes Solutions (a Chemtura Business), which has adopted a greener is better philosophy and has a new Emerald Innovation 1000 flame retardant for polyolefins giving UL-94 V-0 performance. The company"s main market is in the electrical and electronics sector followed by insulation and furniture. This new ingredient is being sold as a drop in substitute for decabromodiphenyl oxide (DE-83R) and decabromodiphenyl ethane (Firemaster 2100R), requiring minimal reformulation. It is a polymeric brominated material.
Flame retardants act to limit fire using different mechanisms such as intumescence, removing or protecting the combustible material, cooling by an endothermic reaction (e.g. aluminium hydroxide) and interrupting the gas phase reaction of oxygen. Professor Rudolf Pfaendner has been studying the effects of flame retardants on photo-oxidation of polymers. As one example, brominated flame retardants tend to be less stable in processing than the polymer itself, and can form photoreactive radicals which accelerate degradation and can de-activate other additives like HALS by reacting. This can be taken into account in formulation, for example by using a form of HALS with lower basicity and microencapsulating the flame retardant. Mineral fillers, which have flame retardant effects, may also render the polymer more sensitive to oxidation and should be compounded accordingly.
Kabelwerk Eupen has been studying new materials for fillers as synergists with ATH and MDH in cable applications. Organoclays in nanocomposites have a high char formation rate and work by migrating to the surface to form a barrier, when combined with another flame retardant they can impart excellent properties. In one experiment with ATH the nanocomposite imparted much lower flame spread and non-dripping properties.
In some applications like packaging and agricultural films, an anti-fogging agent is used to limit water condensation. The issue for packaging is appearance and for greenhouse film water droplets can limit light transmission or focus it on small areas causing burnt plants. Croda Polymer Additives has studied this by looking at the surface energy of different materials: for water it is 72 dynes/cm at 25C, and it is much higher for metals like copper, but lower for polyolefin materials (in the order of 30 dynes/cm). If the polymer surface energy is raised it will cause the droplets to spread out in a fine mist, but not eliminate the problem. Anti-fogging additives disrupt the surface of the water droplet and improve wetting of the polymer surface and a variety of food-contact approved chemicals are used for this purpose. Agent selection is more difficult in PP due to the higher processing temperature and the increased additive migration issues with this polymer. Croda assessed a number of surfactants for hot and cold anti-fogging activity in PP and two glycerol esters performed best. They are being offered in a combination as Atmer 7373 with a PP carrier.
The University of Alicante has been investigating the use of the natural substances carvacrol and thymol (cyclic terpenes) as antimicrobial agents in packaging. The theory is that active packaging would release chemicals to slow the deterioration of food. In this study, thymol or carvacrol was melt blended with PP at different concentrations then tested for standard performance, anti-oxidant and antibacterial properties. The elastic modulus of compounds was lower, possibly due to a plasticising effect, and the effective antimicrobial concentration was 8%.
The organo-phosphorus PEPQ processing stabiliser from Clariant acts as an antioxidant, has high solubility in polyolefin, low haze, suppresses yellowing and allows high temperature processing. In tests at 0.07% in PP with 0.05% phenolic antioxidant and 0.1% calcium stearate it showed around 30% better melt flow index than Phosphite 168, with dramatically better results on yellowing after more than one processing cycle.
30% of processing costs are energy, so it makes sense to add processing aids like the additives from Sasol Wax, which are synthetic chemicals produced by the Fischer Tropsch process from natural gas. EnHance is a linear polymethylene soluble up to 8% in the polyolefin matrix. CeraCarb is a low molecular weight additive aimed at the recycled plastics market and suitable for black materials, it also gives improved gloss.
Dow Corning, a subsidiary of Multibase, provides silicone masterbatches to improve processing and surfaces properties (improved scratch resistance and soft, silky feel). The latter can be particularly useful in automotive interiors. The masterbatch can contain up to 50% silicone and the carrier matrix polyolefin should be as closely matched as possible to the resin it is to be used in. Stabilisers are required to provide a wide process temperature window.
Highly branched carbon black can be used to impart conductive properties to polyolefins. Polymers are natural insulators, which can lead to a build up of static. This charge can be dissipated by making the plastic conductive using a connecting network of carbon black particles, for example from Timcal. Carbon black can carry a charge and will confer conductivity at the percolation threshold. Different grades have different levels of activity from low acetylene blacks to ultra conductive additives and the whole range of properties of the plastic should be considered before making a selection.
There are many ways to enhance polyolefin performance using expert compounding knowledge and additive selection. These topics will be up for debate at the next AMI conference on Polyolefin Additives, which takes place 10-12 September 2013 at the Hotel Nikko in Dusseldorf, Germany.
Polyolefin Additives 2013
10-12 September 2013, Hotel Nikko, Dusseldorf, Germany
Web site: http://www.amiplastics.com/events/Event.aspx?code=C532&sec=3231
Author and contact for further information:
Dr Sally Humphreys
Business Development Manager
Applied Market Information Ltd, AMI House, 45-47 Stokes Croft, Bristol, BS1 3QP, UK
Tel: +44 117 924 9442 Fax: +44 117 311 1534
Web site: www.amiplastics.com