Stress Cracking and Crazing

Environmental stress cracking is the cracking of certain plastic products that becomes exposed to a chemical agent while it is under stress. This effect may be caused by exposure to such agents as cleaners or solvents. The susceptibility of affected plastics to stress cracking by a particular chemical agent varies considerably among plastics, particularly the TPs. 

It is possible with solvents of a particular composition to determine quantitatively the level of stress existing in certain TP products where undesirable or limited fabricated-in stresses exist. The stresses can be residual (internal) stresses resulting from the molding, extrusion, or other process that was used to fabricate the plastic product. Stresses can also be applied such as bending the product. As it has been done for over a half century, the 

Previously no stress or applied stress lasting 16 hours with sample coated with vegetable oil prior to testing for the short-term stress-strain behavior shown. 

TP cracking develops under certain conditions of stress and environment sometimes on a microscale. Because there are no fib- 

For the designer it is not important whether cracking develops upon exposure to a benign or an aggressive medium. The important considerations are the embrittlement itself and the fact that apparently benign environments can cause serious brittle fractures when imposed on a product that is under sustained stress and strain, which is true of certain plastics. 

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Good stress-crack and craze resistance, brittle Good processibility, no stress whitening Higher-heat styrenic, brittle... 

VI. Stress Cracking and Crazing in Fluids Summary Problems References... 

In addition to the separate or combined effects of heat, oxygen, and radiation, polymers may deteriorate due to exposure to water (hydrolysis) or different types of chemical agents. Condensation polymers like nylons, polyesters, and polycarbonates are susceptible to hydrolysis. Structural alteration of some polymers may occur as a result of exposure to different chemical environments. Most thermoplastics in contact with organic liquids and vapors, which ordinarily may not be considered solvents for the polymers, can undergo environmental stress cracking and crazing. This may result in a loss of lifetime performance or mechanical stability and ultimately contribute to premature mechanical failure of the polymer under stress. 

Whilst lubrication invariably decreases the frictional work, it is by no means the case that the wear will be reduced. Indeed the wear may increase. Many fluids are capable of introducing stress cracking and crazing in polymers and the wear may therefore increas ei se the polymer becomes more susceptible to mechanical... 

Brittle low thermal capabilities prone to stress cracking and crazing attacked by oxidising acids, oils, esters, higher alcohols, aromatics, chlorinated hydrocarbons and ketones unsuitable for outside use due to weathering combustible. 

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