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I've been doing a hobby project, creating a parabolic solar reflector to heat up a pipe of flowing water. I did this by cutting a stack of parabolas with a CNC router and secured a thin piece of plywood along the curve (imagine an extruded parabola) I then bonded a space blanket (emergency blanket) with PVA to the plywood.

Initial tests worked very well, it was actually burning the plastic pipe I originally used so have since changed to copper.

The issue is that the space blanket seems to have deteriorated (the reflective foil has gone clear) at points where the glue has not set properly (places where there is a build up of PVA and has stayed wet)

My suspicion is that the wet PVA is somehow eating into the foil lining, so I need a new type of glue suitable for this application. Has anyone any idea of something that is low cost and won't cause problems?

Thanks in advance!

_

Extra info from wiki on space blankets: "The material consists of a thin sheet of plastic (often PET film) that is coated with a metallic reflecting agent, making it metallized polyethylene terephthalate (MPET)"

Max Peglar-Willis
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    Put the glue on the reverse side. – Solar Mike May 17 '20 at 10:49
  • You are describing "de-lamination" of the metallic layer from the plastic film layer. This might be because of chemical reaction or it might be because the adhesive has no flex when the film shifts due to heat. It may also be due to leaching of the plasticisers from the film causing the bond to weaken. – Transistor May 17 '20 at 12:47
  • Seal the plywood with three coats of laminating epoxy and let cure for a week. Wash thoroughly with soapy water - pressure wash it if you can. I would try [high temp lokweld](https://www.yourautotrim.com/1galohitehe.html?utm_source=1galohitehe&utm_medium=shopping%2Bengine&utm_campaign=googleproducts&gclid=CjwKCAjwwYP2BRBGEiwAkoBpAtB1RZ1RCv6vFhcRJ2mp96X0Ar7xy8LzIGNbmMJ6ITWiM5u_1HO3wBoCF4wQAvD_BwE) spray glue applied to the epoxied wood. Let dry at elevated temps in the sun temps for a few minutes, then move back inside and apply the film. Consult mfg for compatibility or special instructions. – Phil Sweet May 17 '20 at 13:34
  • You can also do a lot better than space blankets. Vivosun and others make weatherproof, durable reflective Mylar films. – Phil Sweet May 17 '20 at 13:43
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    Phil, your comment contains enough valuable information to be presented as an answer. In combination with Solar Mike's reversal suggestion or your reference for a different product, Max has a good chance of success. – fred_dot_u May 17 '20 at 16:02
  • Many thanks for all your suggestions, I was not aware that the foil had a orientation if I'm honest, I will give that a try. The film that Phil suggests look very promising also and are low cost so I may purchase some of this! Phil, can I ask if the method of bonding you suggested is also what you would suggest with the mylar film? Thanks in advance! – Max Peglar-Willis May 21 '20 at 12:25

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