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Name: Jac
Status: other
Grade: other
Location: IL



Question:
Once crazing has occurred is there any process to clarify the Plexiglas and restore the surface?


Replies:
PMMA (Plexiglas is a brand name for PMMA) melts at a fairly low temperature (~130C). For simple geometries, you could melt it in an appropriate mold or jig and allow it to re-harden. I recommend you put the piece in a furnace at 60C for a day or so to drive off moisture first -- water vapor can evaporate and cause bubbles to form. Glass is a good mold/jig material as PMMA will demold readily from it once cooled.

Safety note - If your PMMA is for some safety feature, such as a windshield or eye protection, I do not recommend you try to repair it. There still could be strength irregularities in the re-cast piece. It is safer to just replace it.

Hope this helps,
Burr Zimmerman


Jac,

For surface cracks, there are many products out there that combine fillers (usually some microbeads of the same material to be filled, or dissolved polymers -again of the same material to be filled) along with some solvent. The idea here is to fill in the cracks of the polymeric material and fuse the filler material to the base with the help of the solvent. When the solvent evaporates, the filler material - having the same refractive index as the base, will appear to have "healed" the cracks. Do not expect that this "healed" material will be as strong as the original - this is mostly a cosmetic fix, the cracks have been partially filled in to the point that it passes a visual inspection, but the material is still weak at this particular point.

For inside cracks such as when the material has crazed due to cold drawing (pulling at the material below its glass transition) or impact, annealing (especially under pressure) may fuse the microfissures - however, the proper annealing temperatures and pressures will have to be investigated.

Greg (Roberto Gregorius)


Hi Jac,

I am unaware of any process that can eliminate surface crazing of Plexiglas (i.e. polymethylmethacrylate or "Acrylic"), to "like new" condition. There are several possible methods, such as heating to the melting point to fuse the micro cracks, and treating with a solvent such that can dissolve the surface of the acrylic object, such as trichloroethylene, methylene chloride, or tetrahydrofuran (the only three common solvents that can dissolve acrylic). But although these methods may be able to "heal" the crazed surface, they would also likely cause other damage.

Regards,
Bob Wilson



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