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Environmental stress cracking of plastics

by:CSSSLD     2021-01-23
Part of the crystallization of polymer, environmental stress cracking olefin plastics such as PE, PP, PE, in particular, stress cracking is very sensitive to the environment. For PE, environmental stress cracking resistance is to evaluate the long-term service life of one of the most important indicator. Different kinds of injection molding processing PE with different structures, environmental stress cracking resistance may have bigger difference, when the choice should be to determine according to application requirements, should make modification for the PE material when necessary.

solvation effect refers to the polymer molecules and solvent molecules acting force between each other, if greater than between polymer molecular chain reaction and the solvent molecular reaction between polymer molecular separation can be dissolved in a solvent. For example different molecules can form hydrogen bonds between the two functional groups, solvation effects can occur. So we can know that, if a polymer is acidic, and contact with the solvent has basic reactive, and strength is quite, between functional groups in the formation of hydrogen bonds, the polymer will be dissolved in solvent.

solvent stress cracking, refers to the plastic products under certain stress, the stress cracking caused by solvent, even though the solvent on, not affected by the stress of the polymer without or just in the plastic surface layer cause swelling, also the stress cracking phenomenon happens. Cracking phenomenon is the result of the products in excessive deformation under the action of stress, in addition to the type of chemical medium, stress factors such as time, and the size of the stress and temperature, the properties of the polymer and the structure defects is an important intrinsic factor. Can produce stress cracking of reagent vary with different plastic.

solubility parameter can approximate labeled solvent molecules or reaction between polymer molecules, the unit should be paid attention to when using the difference. The difference of the polymer and solvent can be used as a judge on the basis of a plastic solvent resistance solubility parameters can be better applied to heat or no heat effect of non-polar system, however, for polymers can form strong polar bond between solvent and hydrogen bonding system shall not apply. Plastic materials, solvent resistance is one of the best materials such as ptfe, the second is the PPS.

chemical medium erosion of polymer, in addition to the swelling and dissolving two forms, there are two other related to stress damage forms, namely, environmental stress cracking and solvent stress cracking. Environmental stress cracking, refers to the plastic products in stress and non solvent, under the function of active medium caused by the products surface cracking phenomenon. Products by stress from the products is inevitable in the process of forming residual stress, thermal stress, or metal insert in the interface stress and external stress, also may be both.

the crystallization of the polarity of polymer and solvent polarity, due to the interaction when gives off a lot of heat, so without heating, dissolving process can be carried out in at room temperature, such as polyamide at room temperature can be dissolved in isopropyl alcohol, butyl alcohol, formaldehyde, etc. And such as polyvinyl chloride (PVC), he was of medium polarity of plastic injection molding processing, the non-polar paraffin and the strong polarity of carboxylic acids and alcohols has larger resistance, and some of the aromatic hydrocarbons such as benzene, ketones, ethers these medium polarity solvent can make its swelling, can dissolve polyvinyl chloride solvent at room temperature with ring already ketone, tetrahydrofuran, etc.

stress refers to the tensile stress, but it is far below the normal stress of the stress value. And active medium is a solvent, which is in contact with the no load sample does not have the obvious swelling effect of reagent, such as some surfactants and other organic liquid, it is possible that the gas and solid. Some environmental factors, such as sunlight and industrial gases can also be a result in the crack of the products of the active medium, so also known as environmental medium.

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