Rearch On The Preparation And Properties Of Poly (Butylene Terephthalate) Composites

Poly(butylene terephthalate)(PBT),as a kind of engineering plastics,is widely used in electronics,automobile parts and other fields due to its high strength,good chemical corrosion resistance and processing performance.With the increasing concerns on environmental protection and the demand of energy and environment sustainable development strategy,the recycling and reusing of polyester materials has aroused extensive attention among industrial and academic community.However,the high-value use of recycled PBT materials is limited in industrial due to the disadvantages such as low notched impact strength(4 k J/m²),low heat resistance and lack of functionality(such as poor antistatic property and ultraviolet(UV)stability)etc.In view of this,this topic takes recycled PBT materials as research object and the ethylene-vinyl acetate-glycidyl methacrylate copolymer(EVMG)as main toughening material,and then further compounds with glass fiber(GF),epoxidized carbon nanotubes(e-CNTs)and titanium dioxide nanohybrids(i.e.TiO₂@SiO₂-g-EVMG)to make a series of PBT functional composites with high toughness.The primary objectives of this work were to provide some new ideas to improve the physical-mechanical properties of recycled PBT and expand its application fields.It is also expected to provide some new ideas for the study on modification of recycled polyester.The main contents are summarized as follows:Firstly,recycled PBT/EVMG blends were prepared by reactive melt-blending and the PBT/ethylene-vinyl acetate copolymer(EVM)blend was used as a reference.The effects of EVMG on the mechanical properties,crystallization and microstructure of PBT/EVMG blends were discussed and the toughening mechanism was studied in detail.The epoxy groups on the EVMG molecular chain can react with PBT in the melting blending process,and the in-situ formed EVMG-g-PBT copolymers could effectively improve the compatibility between EVMG and PBT.Compared with the dispersed size of EVM phase(2-5?m)in PBT matrix,the dispersed size of EVMG was as small as 0.5?m.The smaller size of EVMG and the smaller interparticle distance can effectively induce the plastic deformation of PBT matrix,thus achieving a significant toughening effect.For example,the notched impact strength and elongation at break of the PBT/EVMG blends with 20 wt%EVMG increased by 14 and 7times,respectively.Furthermore,GF was incorporated to further improve the strength of the PBT/EVMG blend.Compared with pure PBT,the PBT/EVMG/GF composite possessed high tensile strength(44 MPa),and the notched impact strength and flexural strength were increased by 520%and 100%,respectively.In addition,the heat deformation temperature of the PBT/EVMG/GF composite reached 176°C,thus showing excellent comprehensive performance.Secondly,based on the PBT/EVMG system,a small amount of epoxidized nanotubes(e-CNTs)and chain extender were further applied through a continuous processing technology with multiple reactions.The synergist toughening mechanism of EVMG and chain extender on PBT and the optimization of chain extender on the conductive behavior of the composites were systematically studied.The research showed that after the chain extendsion of PBT,long-branched PBT chains and even partially crosslinked micro-structures were formed,which resulted in a significant increase of the melt viscosity of PBT matrix and the tensile strength of the PBT composites.Meanwhile,the dispersed size of EVMG phase and the interparticle distance were further reduced due to the increase on the melt viscosity.Thus,the PBT composites exhabit a much better toughness(the notched impact strength reached to 88k J/m² and the elongation at break was about 300%).In addition,e-CNTs nanohybrids can selectively dispersed in the PBT matrix by controlling the reaction sequence between different components and the conductive network of e-CNTs in PBT phase was easier to form.The conductive percolation threshold of the composite was reduced by about 30%.Finally,TiO₂@SiO₂-g-EVMG nanohybrids with core-shell structures were prepared by coating and grafting techniques,in which the thickness of SiO₂ shell was about 10 nm and the grafting degree of EVMG was about 6.2 wt%.Then,a series of PBT/EVMG/TiO₂(P/E/T)and PBT/EVMG/TiO₂@SiO₂-g-EVMG(P/E/T-E)nanocomposites were prepared by melt-blending.The effects of nano-filler contents and types on the microstructure,mechanical properties,UV shielding and UV resistance of PBT/EVMG composites were systematically studied.The research showed that TiO₂@SiO₂-g-EVMG nanohybrids were selectively dispersed in the EVMG phase due to its good compatibility with EVMG.The addition of TiO₂nanoparticles and TiO₂@SiO₂-g-EVMG nanohybrids both can improve the tensile properties of composites.However,due to the more uniform dispersion of TiO₂@SiO₂-g-EVMG nanohybrids,the P/E/T-E composite has higher fracture toughness than P/E/T.In addition,both P/E/T and P/E/T-E nanocomposites have excellent UV shielding properties.Moreover,due to the isolation effect of SiO₂-shell and the selective dispersion of nanohybrids,TiO₂did not contact the PBT matrix directly in P/E/T-E nanocomposites and which avoids the photocatalytic degradation,thus leading to an excellent UV resistance of P/E/T-E nanocomposites.