10 November 2008

Biocide for Wood Plastic Composites

Longer lifespan with Lanxess additive MPT 11

Specialty chemicals group LANXESS AG is introducing a new biocidal product on to the market that can significantly increase the lifespan of wood plastic composites (WPCs). WPCs are comparatively new composites made of wood and thermoplastics which are enjoying high rates of growth worldwide due to their diverse and cost-effective range of potential uses. Specially tailored to WPC applications, the additive Preventol MPT 11 from LANXESS is based on a careful combination of materials that provides the organic material with effective protection from fungi that can cause discoloration and damage.

Wood plastic composites have a 60 to 80 percent wood content in the form of chips, fibers or even finer particles that are combined with thermoplastics such as polypropylene, polyethylene or PVC insignificantly smaller proportions of around 20 percent by weight to create a extrudable material. WPC granules can then be processed using extrusion and even injection molding. WPCs offer an impressive flexibility of design compared to natural wood. Compared to solutions based on plastics alone, WPCs score points due to their lower price, interesting tactile quality, attractive appearance and sustainability. Their range of applications is correspondingly diverse – currently, wood plastic composites are used primarily in North America, but are also becoming increasingly popular in Europe and Japan in the production of decking, façade cladding, railings, window frames and decorative profiles, in addition to applications in the automotive and furniture sectors.

However, the use of wood – a natural raw material – poses a challenge in terms of this material’s susceptibility to microbes. In order to achieve an attractive appearance and feel, WPC panels are often brushed and, in practice, the protective plastics matrix undergoes a gradual process of wear and tear. Both of these processes can expose wood fibers, allowing dampness to permeate the material. Particularly when WPCs are used in outdoor environments – and such usage constitutes the lion’s share of WPC applications in North America – untreated composites can therefore become just as fertile a breeding ground for fungi as natural wood over time. In the best case scenario, this simply results in discoloration, but it can often cause mold to form and this in turn impacts on the slip-resistant quality of the material.

One effective means of tackling this problem is to equip WPCs with mold-repellent additives as early as the production stage. However, inorganic preparations such as zinc borate should be viewed with caution as they must be used in extremely high dosages and therefore make recycling and thermal recycling more difficult. In contrast, organic biocides generally have lower active concentrations. However, the high extruder temperatures of up to 200 °C and the need for rapid and homogeneous distribution within the compound despite the lower dosage means that the use of such products in wood plastic composites places very high demands on the formulation. Preventol MPT 11 is able to meet this challenge. It is very effective in blocking the growth of a range of microorganisms including Penicillium funiculosum and Aspergillus niger. The new biocidal product is effective in low dosages and is simply added to the extruder alongside the other additives (usually bonding agents, UV protection agents and pigments). The additive is then distributed throughout the composite rapidly and very effectively. This is an efficient means of increasing the lifespan of premium WPC products – the adverse effects of mold or microorganisms that cause discoloration are reduced dramatically and costs generated by complaints are minimized.

LANXESS is to initiate an approval process for Preventol MPT 11 as part of the EU’s Biocidal Products Directive (BPD). Users will then not only benefit from the technical expertise of an additive specialist that can look back on over 100 years in material protection, but will also be freed of the burden of the administrative outlay associated with submitting their own registration. Preventol MPT 11 is not the only product that LANXESS offers for manufacturing WPCs. For example, heat-resistant inorganic pigments from the Colortherm range are also used in these versatile composites.

Source: moneycontrol.com, press release, 2008-11-06.

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