The global demand for thermoplastics is expected to grow by around 100,000 tons by 2015, driven by the developing economies. Polyethylene comprises 35% of this market and polypropylene is 24%, according to leading market consultant Noru Tsalic of Applied Market Information (AMI). This is an annual increase of 5.6%. The key applications for PE are packaging at 69% and infrastructure at 11%, while for PP the percentages are 43% in packaging and 11% in automotive and appliances. This market information was discussed at the AMI conference on Polyolefin Additives, which took place in October 2011 in Cologne, Germany.
The leading material suppliers conduct extensive research, like Borealis Polyolefine. Molecular structure, processing and additives all affect properties. Stabilisers and modifiers need to be compatible with the polymer, have high solubility and low migration rate and meet all safety standards. The range used in polyolefins includes antioxidants for processing and long-term stabilisation, UV stabilisers, antistatic, slip agents, nucleating agents, flame retardants, impact modifiers, lubricants, foaming agents, fillers and reinforcements. It is also important that recipes take account of synergistic or antagonistic effects of additive combinations, for example hindered amine light stabiliser (HALS) is antagonistic to sulfur antioxidants. Some additives have dual effects, for example nucleating agents can improve thermal stability, perhaps because of the increase in crystallinity. Fillers are particularly important as the chemical nature, particle morphology and surface treatment can all affect material performance and additive interaction.
Analysis carried out by Basell Deutschland a LyondellBasell Company, has shown that polymers now account for around 19% of the materials in cars, which amounts to around 170 kg per vehicle and 60% of this is PP. The industry trends are towards manufacturing in low cost regions and light weighting, while cost dictates the types of materials used in different applications. For example, in high end cars there wil be foam-backed skin foils, in the middle range there is a plastic surface with soft-touch paints and at the lower end the plastic is uncoated. Basell Deutschland has developed new soft touch PP compounds for automotive interiors which meet the latter requirements. The base resin, Softell, has a very fine dispersion of elastomer particles in PP giving low gloss and high Shore D properties (low scratch and mar), whilst maintaining processability in injection moulding. As it does not require coating it has the potential to reduce costs.
BYK Chemie has developed additives for reducing odour and fogging in automotive applications. During extrusion the carrier releases active substances, which form microfoam under the raised temperature and shear stress. In this process the volatile organic compounds and odour components are wetted. Downstream the microfoam collapses and these components are released in degassing of the extruder. Thus BYK-P 4200 acts as a sort of stripping agent.
In packaging, Danisco has efficient anti-fogging solutions for both PE and PP, which prevent the formation of water droplets on the inside of the film (this is also used in agricultural applications). Chemically-modified fatty acids are used, with a tailored polarity to control migration. The antifog works by reducing the surface tension at the water/polymer interface: in effect the condensed water forms a thin continuous film and there is no loss of transparency. If the antifog is to be used in a complex multilayer construction then it needs to be added to several layers, because the sealing layer where it needs to be active is usually only around 8 microns thick.
Silanes are used in polyolefins for crosslinking and polymer-filler coupling, while silicones are employed to improve processing and properties like scratch resistance, for example the Genioplast range from Wacker Chemie. Other benefits from the use of silicone additives are the soft dry surface feel, low fogging and improved mechanical properties. They are suitable for use in applications such as PP/talc compounds for automotive interior components like the dashboard, trim and central console.
Antioxidants are key to performance. A variety of phosphites are used including the liquid trisnonyl phenyl phosphite (TNPP) and commodity solid phosphite (SP-1). TNPP does not bloom and has global indirect food contact approval (GRAS). The Dover Chemical Corp. has developed a new Liquid Green Phosphite (LGP-11), which is a high molecular weight molecule with low migration, is biodegradable, contains no alkylphenols, and has process and hydrolytic stability. This is currently being patented.
The leading research company in polyolefins is Norner in Scandinavia. The company has recently led research with partners from Sintef, Nexans and BrederoShaw looking at the effect of service conditions on the consumption of antioxidants in polyolefins. The project was based on the performance of PP coatings for oil and gas pipelines, where the pipes require direct electrical heating to avoid the formation of hydrate and wax inside. The specification is a 25 year service life at temperatures up to 115C and at a sea depth of around 350 m. Different types of PP block copolymer were tested including a 25% glass fibre grade. The results showed that discoloration was affected by wet or dry conditions, time and water depth. Chemical analysis using HPLC and GC revealed the antioxidant consumption in the different types of PP under different conditions, for example there was a 57% consumption of one antioxidant in the glass fibre-reinforced PP during processing. There was a significant effect of raising the sea water pressure conditions (simulating depth) on the loss of some antioxidants. The results of this study indicate the best antioxidants for long-term use in deep sea pipe coatings.
Polyolefins burn well with high heat capacity; therefore flame retardants are important for some products. PP can be a challenge as it is already crystalline and adding filler-type flame retardants can make the material more brittle. THOR has developed a new non-halogen flame retardant to address some of the weaknesses of existing FR systems. The new AFLAMMIT grades can be used in applications such as thin wall and films, and are based on organic phosphorus chemistry. In tests in LDPE the LOI was around 30 at 5% loading, and there are synergistic effects with other additives like the NOR HALS Flamestab from BASF and Hostavin NOW XP PILLS from Clariant. In PP a loading of 8% gave an LOI of about 26. Various factors affect the loading required including the film thickness, the presence of fillers like carbon black and titanium dioxide, and the MFI.
UV stabilisation is critical in many products. Cytec has produced several tailored products for different markets including CYASORB UV-3853 for PP/TPO automotive interiors to improve gloss retention and CYASORB THT-6460 for agricultural films to resist acid pesticides and mechanical stress. Cynergy R300 is for rotomoulding applications.
AkzoNobel supplies organic peroxides for a variety of functions in polyolefins including modifying viscosity, to facilitate foaming, and in crosslinking for applications such as cable and PEX pipes. In the mechanism of action the peroxide is initiated forming radicals, which then abstract H molecules from the polymer, in turn generating polymer radicals. There are a variety of radicals which can generate polymer radicals including alkyloxy, phenyl, methyl, acyloxy and cumyloxy. In reactive extrusion the peroxides are combined with the base polymer and the reaction occurs in the extruder followed by degassing. Crosslinking improves properties such as impact and stress-crack resistance, temperature and chemical resistance. In the cable industry there is a shift to in-house compounding for medium voltage (MV).
Sustainability is a key issue worldwide. RockTron is using fly ash from waste incineration to produce fillers. The MinTron particles comprise solid glass spheres and the product is developed to customer specifications, for example from 5-9 microns or 8-14 microns. MagTron is a spherical magnetite particle measuring 55 microns CenTron is hollow glass spheres of 140 microns. Surface modified grades are available and these products are being used as fillers.
The foaming process comprises several steps starting with nucleation, then bubble growth and stabilisation. A crosslinking agent can be added after foaming. Polimeri Europa is testing blends of polyethylene and EVA in foams and comparing properties at different percentages. The vinyl acetate content has a big influence on the final foam properties. LDPE and LLDPE are used in blends to improve the performance of both, for example LDPE is easier to extrude and LLDPE is more heat resistant. A new EU plastics regulation came into effect on 1st May 2011. Keller and Heckman have reviewed the implications for the industry, for example, here are some of the definitions
· Article 3(8). Additive, “a substance which is intentionally added to plastics to achieve a physical or chemical effect during processing of the plastic or in the final material or article; it is intended to be present in the final material or article”.
· Article 3(8). Polymer production aid (PPA), ““means any substance used to provide a suitable medium for polymer or plastic manufacturing; it may be present but is neither intended to be present in the final materials or articles nor has a physical or chemical effect in the final material or article”.
· Article 3(9). Non-intentionally added substances (NIAS) are defined in ““means any substance used to provide a suitable medium for polymer or plastic manufacturing; it may be present but is neither intended to be present in the final materials or articles nor has a physical or chemical effect in the final material or article”.
K-Tron has reviewed the issues with material quality and additive dispersion. The company recommends implementing quality control on deliveries and making sure that equipment is functioning to the required standard. It is important to consider the history of the material and factors such as storage conditions, thermal exposure and mechanical treatment, which can cause problems like particle agglomeration. During conveying there can be issues with many aspects including the amount of air coming through and build up in the connecting pipes. The whole system needs to be set up correctly for each new operation.
Dr. Oleg Kulikow of the Universität Der Bundeswehr Munchen has studied polymer processing aids (PPA): these have greater adhesive properties to metal than molten polyolefins and form a lining at the die surface during extrusion. Hydrophobic materials like fluoropolymers are often used as lubricants, however in natural joints the lubricant is hydrophilic. A new PPA is proposed comprising polyethylene glycol and silanol, and relatively cheap to produce.