Preparation Of Core-shell Structured Polymer And Its Effect On Toughening Modification Of PBT Resin

Polymer materials with their excellent performance are gradually to contend with metal materials. While the perfect features of plastics are maintained, its drawbacks should be overcome in order to apply it in different areas. Poly(butylene terephthalate)(PBT) is an important engineering thermoplastic with superior properties, such as high rigidity, solvent resistance, high rates of crystallization, fine insulation and short cycle times in injection molding, which can be used in automotive interior, electronics and electrical instrumentations, household appliances and communications. PBT is notch sensitive and will fracture in a brittle way when standard notched specimens are tested. Toughness is one important parameter to evaluate whether a polymer can be used as an engineering material. Improving the toughness of brittle plastics has become an attractive topic. Incorporation of rubbery fillers is an efficient way to enhance the fracture toughness. The study of core-shell modifier will have further significance in future.In this study, the acylate copolymer latexes with core-shell structure were synthesized by seeded emulsion polymerization, in which butyl acrylate(BA) was used as the core monomer, methyl methacrylate(MMA) as the shell monomer, and methacrylic acid(MAA) or crylic acid(AA) or none as the copolymerized component in the shell layer. As the results, we get poly(BA/MMA-co-MAA) or Poly(BA/MMA-co-AA)or Poly(BA/MMA), which are indicated as PBMMA or PBMAA or PBMA. The modifier was prepared at a solid content of 50 wt% by a two-stage sequential emulsion polymerization. PBT/(PBMMA or PBMAA or PBMA) blends were prepared through a twin-screw extruder by melting extrudsion. The coagulation content and the instantaneous and overall conversions were determined by gravimetry. The structural properties of the copolymer were analyzed by FTIR and the particle diameters of latexes were measured by dynamic light scattering(DLS). Transmission electron microscopy(TEM) was used for morphological characterization and dynamic thermal mechanical analyzer(DMA) for mechanical properties. Charpy notched impact strength and tensile strength of(PBMMA or PBMAA or PBMA) blends were tested, respectively. Uniform dispersion of rubber particles in PBT matrix was attributed to the good compatibility between PBT and modifier.The results showed that instantaneous and overall conversions of the monomers were all high and the latex systems were stable. PBT/PBMMA(PBMAA) blends, synthesized in this study, increased the notched impact strength of PBT. The notched impact strength of the PBT/PBMMA(PBMAA) blends was better than others, because of core-shell composites of 80/20(BA/MMA) with the functional monomer MAA 1.8% and adding 25% PBMMA contents, and core-shell composites of 80/20(BA/MMA) with the functional monomer AA 0.75% and adding 20% PBMMA contents. The notched impact strength of blends was 7.83 times of pure PBT with the copolymer PBT/PBMMA, and 8.61 times of pure PBT with the blends of PBT/PBMAA. Meanwhile, the tensile strength decreased slightly with the addition of PBMMA(PBMAA) in PBT matrix.We synthesized PBMA and studied its effects, in different core-shell latex particles, on toughening of PBT, and also studied the use of different core-shell content for toughening PBT matrix. The notched impact strength of the PBT/PBMA blend, with the core-shell ratio of 75/25 and adding 16.67% PBMA contents, reached its peak of 75.20 k J/m2, which was 8.64 times of pure PBT. The fractured morphology of the blends showed major ductile deformation of the PBT matrix, being consistent with the impact properties of the blends. Depending on the type of matrix, the amount of carboxyl groups on the surface of the core-shell particles could be regulated during the polymerization. This method of core-shell particles synthesis is promising in achieving desirable compatibilized thermoplastics.