The degradation of polymer molding process
polymer degradation process is the essence of the macromolecular chain structure changes have taken place, such as chain scission, crosslinking and the change of the side group, etc. In the process of forming process, polymer degradation is generally difficult to completely avoid. Polymer degradation will produce the result of the decreased the strength of the plastic parts, plastic parts, change color, crisp, sticky with bubbles and flow lines and other ills, serious will make polymer damage monomers or other low molecular compounds, put a hitch in molding, plastic parts out of use value. In molding process, thermal degradation is a major, and by the stress, oxygen, water and other impurities such as acid and alkali degradation is caused by secondary.
polymer formed in forming process of 3 d mesh structure known as the crosslinking reaction, polymer shape can be obtained by crosslinking reaction. Compared with linear polymers, size polymer in mechanical strength, heat resistance, solvent resistance, chemical stability and plastic pieces of shape stability, etc, were increased. So, to strength, to work in some occasions with higher requirements, such as temperature, creep, crosslinking polymers have a wide application.
in degradation of polymer in molding process, can make the plastic parts of bad appearance, inner quality, shorten the service life, therefore in the process of forming, should as far as possible to reduce or avoid polymer degradation. The quality of the polymer is largely affected by the process in the process of synthesis. For example in the macromolecular structure contains double chain and branched chain, the relative molecular mass dispersion, raw material is not pure or mixed with due to late to purify the bad initiator, catalyst, acid, alkali, or metal powder and so on many kinds of chemical or mechanical impurities, and these will affect the stability of the polymer and the processability go bad.
special polyester, polyether, and polyamide polymer easy adsorption moisture from the air during storage, usually before use temperature and low moisture content should be brought to zero. 01% - 0. Less than 05%. In order to make the polymer under the condition of not easy to produce the degradation processing molding, correctly determine the reasonable processing technology and processing conditions, for those poor thermal stability, molding temperature and decomposition temperature very close to the polymer is particularly important. With drawing method, the polymer molding temperature range will help determine the reasonable processing conditions.
polymer injection molding processing is usually carried out under high temperature and stress. Because of the large molecules polymer is heated and stress effect, or by the trace moisture due to the high temperature, acid, alkali and other impurities and the role of oxygen in the air, the polymer relative molecular weight reducing or macromolecular structure change will happen, such as a chemical change, usually lower the relative molecular mass of this phenomenon is called degradation or cracking.
according to the performance of the polymer, especially the forming temperature is higher, antioxidants, stabilizer and so on should be considered in order to strengthen the polymer's ability to resist degradation. The degradation of polymer in most cases can be harmful, but there are exceptions, for example through mechanical degradation of polymer or between two kinds of polymer monomer grafting or block between polymer compound copolymer, to improve performance of polymer and enlarge its application scope is an example.
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