Polymethyl methacrylate crazing

The acrylic plastics use the term acryl such as polymethyl methacrylate (PMMA), polyacrylic acid, polymethacrytic acid, poly-R acrylate, poly-R methacrylate, polymethylacrylate, polyethylmethacrylate, and cyanoacrylate plastics. PMMA is the major and most important homopolymer in the series of acrylics with a sufficient high glass transition temperature to form useful products. Repeat units of the other types are used. Ethylacrylate repeat units form the major component in acrylate rubbers. PMMAs have high optical clarity, excellent weatherability, very broad color range, and hardest surface of any untreated thermoplastic. Chemical, thermal and impact properties are good to fair. Acrylics will fail in a brittle manner, independent of the temperature. They will suffer crazing when loaded at stress about halfway to the failure level. This effect is enhanced by the presence of solvents. 

Rothwell, Martinson and Gorman have studied the formation of stress induced crazes in polymethyl methacrylate. The sample was initially stressed and held at a strain of 3.5 %. Upon relaxation, SAXS-patterns of 1.5 s were recorded using a linear photodiode detector array. A sequence of selected curves recorded in a plane parallel to the strain direction is shown in Fig. 49. The peak at h = 0.014 is probably due to an... 

Acrylics such as polymethyl methacrylate should be annealed before solvent cementing to minimize the formation of internal stresses that can cause crazing. Acrylic sheets can be annealed by heating in a forced-air oven at about... 

---