Wood Plastics-II

Dr.S.S.Verma writes about the benefits of wood plastics


Most research using wood flour as filler for thermoplastics has been conducted with a limited number of wood species so far, and only a few grades of broad particle-size distributions. To fully exploit the use of wood flour fillers, the full effect of wood species and particle-size distributions must be determined. Commercially produced wood flour has a broad particle distribution. As a result, a comparison of mesh sizes from a commercial supplier of wood flour results in an overlap of particle sizes. Extra screening of the wood flour to narrow the particle-size distribution generally results in a more expensive wood flour; therefore, typical commercial grades include a mixture of particle sizes.
Plastic wood offers several advantages over natural wood. It is generally resistant to rot, mildew and insect infestation. Wood-plastic composites is fastest growing sector of plastics industry and are already widespread in outdoor use for decking, cladding, park benches, etc. There is also a growing market for potential indoor uses such as door frames, trim and furniture. Some plastic lumber is injected with dyes during the production process, which makes stains and paint unnecessary. Wood-plastic composites may be one of the most dynamic sectors of today’s plastic industry. Although the technology is not new, there is growing interest in the new design possibilities this marriage of materials offers. Need is to develop wood plastic composites suitable to all weathers with long life cycles with more load capacity and should be produced faster, better, cheaper, environmentally safe and efficient.
Scientists at the State University of New York’s College of Environmental Science and Forestry are developing a way to add wood fiber to plastic to make it stronger. The process focuses on extracting nanocrystals of cellulose out of woody materials, like trees and willow shrubs, and mixing them with the plastic. All plant materials contain a minimum of 25 percent cellulose and wood from trees is a little higher, between 40 percent and 50 percent. Using cellulosic nanocrystals to strengthen plastics has advantages over the glass that is often used. Glass is heavier, harder on processing machinery and therefore more expensive to work with, and it stays in the ground for centuries. The eventual result will be strong, lightweight plastics that would degrade in a landfill. The cellulose nanocrystals will break down in a landfill in less than 90 days. By adding an ounce of crystals to a pound of plastic, the strength of the plastic can be increased by a factor of 3,000 and in the end, in a landfill, it’s just carbon dioxide and water, which can be taken up and made into more biomass. In addition their use as strengtheners in plastics, the nanocrystals can be used in ceramics and in biomedical applications such as artificial joints and disposable medical equipment.
First, the scientists purify the cellulose to remove substances such as wax and gluey lignin. The cellulose then goes through a homogenizing process, similar to the one used with dairy products. The cellulose is shredded into tiny particles under high pressure, producing nanocrystals – which are measured in billionths of a meter. A viscous, white liquid is produced that goes into a microcompounder, where it is mixed with plastic under high pressure. The team is currently working on refining the surface of the crystals so they adhere better to the plastic and disbursing the crystals throughout the material to achieve the best results. The next step will be to scale the process up to a commercial level.
–Concluded
(Dr.S.S.Verma is from Department of Physics, S.L.I.E.T, Punjab. He can be mailed at ssverma@fastmail.fm)