Preparation And Properties Of Semi-Aromatic Heat-Resistant Polyamide And Its Composites

Polyamide,also known as nylon,is the most widely used engineering plastic.Among them,aliphatic polyamides,such as PA6 and PA66,can be produced by low-cost melt processing,and are currently the most used polyamide.With the introduction of the concept of lead-free solder for surface mount technology and the development of automotive turbocharged engines,higher requirements are placed on the heat resistance of materials.The general aliphatic polyamides melting temperature is lower than 260°C,so they have not been able to meet the requirements of the above two fields.Fully aromatic polyamide,which has excellent thermal properties and mechanical strength,is considered to be a high performance polymer.However,the high glass transition and melting temperature of the wholly aromatic polyamide make it impossible to produce by low-cost melt processing,which limits the wide range of applications.In recent years,semi-aromatic polyamides have attracted more and more attention because they combine excellent processability of aliphatic polyamides and good heat-resistant of wholly aromatic polyamides.Commonly semi-aromatic polyamides include poly(p-phenylene hexamethylenediamine)(PA6T),poly(p-phenylene terephthalamide)(PA9T),and poly(p-phenylene terephthalamide)(PA10T),among them,PA10 T is the only bio-based semi-aromatic heat-resistant polyamide,which is especially important today when environmental stress is high.However,the melting point(316°C)of PA10 T is close to its thermal decomposition temperature(350°C),which is prone to decomposition during melt processing and injection molding.Therefore,the development of bio-based semi-aromatic heat-resistant polyamide with a wide processing window and good processing properties has become an urgent problem to be solved.In this paper,a novel semi-aromatic heat-resistant polyamide PA10T/66 which has a wide processing window was synthesized by melt polycondensation using bio-based diamine,terephthalic acid,hexamethylene diamine and adipic acid as raw materials.Then the structure of PA10T/66 was determined by hydrogen nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy,and the salt formation process was analyzed.Based on this,the effects of polymerization conditions such as polymerization temperature,polymerization time,polymerization pressure,stirring rate,gassing time and viscosity increasing pressure on the performance of PA10T/66 were investigated.Finally,the optimal polymerization process was obtained.Through the optimal polymerization process obtained above,we synthesized PA10T/66 copolymer with different PA66 segment content.The physicochemical properties such as physical and mechanical properties,density,water absorption,oil absorption,solvent resistance and melt index and flow properties of the polymer were investigated.The results show that the introduction of PA66 segment into the PA10 T molecular chain can improve the toughness and fluidity of PA10T/66.The thermal properties of PA10T/66 under different PA66 segmental contents were investigated by differential scanning calorimetry,heat distortion temperature test and thermogravimetric analysis.The results show that with the increase of PA66 segment content,the melting temperature of PA10T/66 decreases,while the thermal degradation extrapolation initiation temperature does not change substantially,indicating that the processing window is broadened by introducing aliphatic PA66 segments into PA10 T.Its processing properties are feasible.Then,the thermal degradation kinetic parameters and thermal degradation activation energy of PA10T/66 were determined by Kissinger-Akahira-Sunose(KAS),Flynn-Wall-Ozawa(FWO)and Tang.The thermal degradation mechanism function type is determined by Coats–Redfern integration method as R3 type(phase boundary reaction(spherical)).The isothermal and non-isothermal crystallization kinetics of PA10T/66 at different PA66 segment contents were analyzed by differential scanning calorimetry.The crystal growth mode of PA10T/66 during isothermal crystallization was determined by Avrami equation.The feasibility of the Avrami equation for the isothermal crystallization kinetics of PA10T/66 was confirmed by the Turnbull-Fish equation.The Hoffman extrapolation method was used to determine the equilibrium melting point of PA10T/66 at different PA66 segment levels.Next,the crystal growth mode of PA10T/66 in non-isothermal crystallization was determined by Jeziorny method.The effect of PA66 segment content on the crystallization rate of PA10T/66 under different relative crystallinity was studied by Mo method.The results show that the lower the isothermal crystallization temperature,the higher the cooling rate,the faster the crystallization rate of the polymer;under isothermal crystallization conditions,the crystal growth mode of PA10T/66 is disk-shaped(circular)two-dimensional growth.Under non-isothermal crystallization conditions,when the PA66 segment does not exceed 0.07 mol,the crystal growth mode of PA10T/66 is disk-shaped(circular)two-dimensional growth.When the PA66 segment reaches 0.13 mol,the crystal growth mode of PA10T/66 is fiber(one-dimensional)growth at a low temperature drop rate(5°C/min),and still disk-shaped(circular plate)two-dimensional growth at a high temperature drop rate(10,20,40?/min).In addition,the Avrami equation and the Jeziorny method,Mo method are suitable for describing the isothermal and non-isothermal crystallization kinetics of PA10T/66.The crystal morphology of PA10T/66 was observed by polarized light microscopy.It was found that PA10T/66 has smaller grain size and larger grain density than PA10 T.In order to expand the application field of semi-aromatic heat-resistant polyamide polyamide PA10T/66 and adapt to the market demand,we have carried out glass fiber reinforced melt blending modification.PA10T/66/GF composites were prepared by melt blending using our synthesized PA10T/66 and glass fibre(GF)as raw materials.The cross-sectional morphology of PA10T/66/GF was observed by field-scanning scanning electron microscopy.It was found that the glass fiber and PA10T/66 have good compatibility and the glass fiber is uniformly dispersed in PA10T/66.Then the physical and mechanical properties,flow properties and thermal properties of PA10T/66 were studied by universal sampler,melt indexer,thermal deformation tester,differential scanning calorimeter and thermogravimetric analyzer.The results show that the flow properties of PA10T/66/GF decrease with the increase of glass fiber content,but the physical and mechanical properties and thermal properties are greatly improved.The PA10T/66/GF composite with a glass fiber content of 30% has good fluidity,physical and mechanical properties and thermal properties.Compared with pure PA10T/66,the tensile strength,flexural strength and flexural modulus of PA10T/66/GF composites increased by 141%,99% and 209%,respectively.And the heat distortion temperature under 0.45 MPa and 1.82 MPa load reached 286°C and 244°C,respectively,which was 52°C and 148.8°C higher than pure PA10T/66 resin.Similarly,the isothermal and non-isothermal crystallization kinetics of PA10T/66/GF composites with different glass fiber content were studied by differential scanning calorimetry and Avrami equation,Jeziorny method and Mo method.The results show that the addition of glass fiber promotes the heterogeneous nucleation of PA10T/66 and accelerates the crystallization rate of the polymer.Under isothermal and non-isothermal crystallization conditions,the crystal growth mode of PA10T/66/GF is still disk-shaped(circular)two-dimensional growth.The Avrami equation,the Jeziorny method,and the Mo method can all be used to describe the isothermal and non-isothermal crystallization kinetics of PA10T/66/GF.