Wednesday, March 23, 2011

Plastics in board making

Something that I've found particularly confusing in the research on board construction is what plastic materials can be made use of in construction. There is a stagering array of different plastics with varying chemical inertness, strength and abrasion resistance. It seems that at one end is PVC that epoxy will stick easily and at the other end of the spectrum is Polyethylene which according to most punters is very chemically inert and so epoxy (and most things) will not chemically bond to. ABS, very commonly used as rail material and, at least for Brokites, as stringer material, is towards the PVC end of the spectrum. However, there are two additional factors that appear to be important in working out whether epoxy is going to stick or not and depending on the application it may or may not be desirable - for example, High Density PE ( which apparently is the most widely used plastic in packing material) is perfect for using as vacuum film as epoxy wont stick to it. The additional factors are how rough the surface is and whether you have flame treated the surface (literally pass a flame over the surface). Roughing the surface allows a mechanical bond to occur between the epoxy and the plastic. One source states it as 'scratches are like grab handles for resin'. If you want the plastic to stick to it then rough it up with 40 grit sand paper first. Flame treating oxidizes the surface of the plastic which in turn improves the epoxies ability to chemically bond with the plastic. So despite HDPE being know for peeling easily off resin coated surfaces, according to one snowboard maker, roughing the surface and flame treating creates a great bond with the epoxy. This punter used 1/32" HDPE sheet as the protective bottom layer on the bottom of his snowboard. The other PE derived material which apparently is the dogs balls of plastic to use on the bottom surface has the catchy name UHMP - Ultra High Molecular Weight Polyethylene which is tough, abrasion resistance and slippery. Ideal for the bottom of a kiteboard ....... but apparently v. expensive. Have not tried to price it myself. HDPE is apparently much cheaper and easier to come by as PE ( the PE in PET plastic) is very common. Am going to try to track down some and try on the next board. If anyone knows of a supplier in Sydney that sells 1/32" sheet and thinner film then left me know because, despite it apparently being ubiquitous, I can't find a supplier. Maybe I'm just not looking for the right keywords but I thought that HDPE would have done it......... UPDATE - thanks to JMF on kiteforum I've got a great update to the search on bottom sheets. 'PBT' plastic film is the stuff used as bottom sheets on snowboards, wake boards, and most importantly Brokite boards!!!! Still looking for an AU supplier if anyone knows of one. Cheers Matt

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