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The control and application of ester exchange reaction

by:CSSSLD     2021-01-23
Polyester and the polymer blends such as PC, PA, ester exchange can occur. Ester exchange reaction, amide, in a sense, the reaction of increasing the compatibility of the blend components, but it also promotes the degradation of macromolecular reaction, to a certain extent, reduce the injection molding processing material mechanics performance. Polyester with PE, PP, PS, PPO, ABS polymer blends, such as by ester exchange reaction with compatibilizer, increase the compatibility with other polymers, actually also reduces the relative molecular mass of the polyester.

PET and HDPE, LDPE, LLDPE blend preparation performance of different alloys. In the preparation of PET/PE alloy, all needs to use the compatilizer, available compatilizer of graft copolymer of EVA and EAA and PE. In PET and LLDPE alloy, because the performance of the blend composition is different, make the performance of the alloy, the three systems, the change for the amount of PE on the mechanical properties of alloy influence law is not the same.

add mPE in PET/HDPE system - g - GMA, toughening of polyolefin-g-mah/has obvious effect, the tensile strength, bending strength, with the size of PE consumption reduce also less compatible system. Methyl glycidyl ester of acrylic acid grafted copolymer suitable for polyester modified PE, because the GMA of epoxy group and more easily than anhydride polyester end carboxyl, carboxyl reaction. Epoxy and polyester carboxyl reaction not only increase the compatibility of PE and PET, but also makes the molecular chain growth, to a certain extent, improve the strength of the alloy that is: HDPE increased dosage of HDPE/PET alloy impact strength to rise sharply, and the bending strength, tensile strength decreased very small internal causes.

with the increase of dosage of LDPE, the tensile strength of the alloy decreased, while the breaking elongation and impact strength of PET/HDPE system are similar, but the extent of change is smaller. Adding compatilizer system, its performance obviously better than without compatilizer systems. PET/PE alloy has good liquidity and high impact strength, increases the PET's toughness. Adjust system composition, mechanical properties can be obtained balance of the alloy.

for the same blending system, the compatibility of different compatilizer role is different, the main reason is that different molecular structure of compatilizer, namely the polar groups of different reactivity, formed by reaction with polyester chemical combining site, reflects the change of the mechanical properties of the blend of body. Dosage of HDPE in HDPE/PET alloy, alloy decrease in the tensile strength, modulus, breaking elongation and impact strength with the increase of the dosage of HDPE fall first, HDPE dosage is very low, when 50% dosage of HDPE is more than 50%, breaking elongation and impact strength of the alloy increases, compatilizer dosage has a great influence on the mechanical properties of the alloy.

with single functional groups grafted copolymer as a compatibility agent, the possibility of ester exchange reaction is lesser, compatilizer reaction with polyester end groups is the result of the increase of polyester relative molecular mass. Control the ester exchange reaction, can from the following several points cut: 1. Reduce the melt blending extrusion temperature, avoid high temperature degradation. 2. Reduce the residence time of material in the screw injection tooling, melt the longer you stay, the greater the probability that the ester exchange reaction. 3. Avoid adding additives with catalysis. 4. Choosing a graft copolymer as compatilizer, should choose can only react with polyester base at the end of copolymerization monomer.

HDPE/PET bicomponent system, system of not adding compatilizer, PET show uneven, particles dispersed in continuous phase, HDPE two phase boundaries clear, PET particle size decreases, the compatible function of EAA to perform better, the dispersed particle size smaller, polyolefin-g-mah/now at the mechanical properties of impact strength increased significantly. Melt extrusion of polar monomers and mixed composition prepared by the graft copolymer as a compatibilizer, the compatibilizing method is generally used.

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