Studies On The Preparation Of PET/PA6 Alloy By Reactive Extrusion And Its Performance

Polyester and polyamide are the two widely used engineering plastics and synthetic fibers.Polyamide has excellent thermal and mechanical properties,but high processing shrinkage and high cost.Polyester has the advantages of low cost,high rigidity,good creep resistance and dimensional stability,but inferior impact resistance,wear resistance and antistatic properties.Polyester/polyamide alloys are expected to combine the advantages of these two types of polymers and improve the overall performance,thereby enriching its applications in the field of engineering plastics and composite fibers.In this study,polyethylene terephthalate(PET)and polyamide 6(PA6),which are the most commercially available,were used as raw materials to prepare alloys.However,PET and PA6 are typical incompatible systems owning to their macromolecular chain structural.Previous studies have used catalysts to promote the ester-amide exchange reaction and generate compatibilizer to improve the compatibility.However,it usually takes up to several hours.This work intends to use modified PET as a raw material to improves the compatibility and thus the overall performance of the alloy.A series of polyester/PA6 alloys were prepared by a twin-screw extruder using PA6,PET and PET modified with sulfonic acid groups(CDP)as raw materials.Use solubility experiment,SEM,FTIR and 13C NMR and other test methods to characterize its compatibility and structure.The research results show that the CDP/PA6 alloy prepared by reactive extrusion has a dispersed phase with samll size and irregular shape.Its compatibility is far better than that of the PET/PA6 alloy.The mechanism of increased compatibility is as follows:the benzenesulfonic acid group on CDP attacks PA6,and a polyester/nylon graft copolymer is formed in a short time through this one-step reaction;this copolymer acts as a compatibilizer,greatly improving CDP/PA6 alloy’s compatibility.When the content of CDP and PA6 in the alloy was similar,the largest amount of graft copolymer was generated,rsulting in the best compatibility.It has been found that BOZ can reduce the size of the dispersed phase in this system,but the improvement in the compatibility is insignificant.The crystallization behavior of the polyester/PA6 alloy was studied.The melting point,crystallization temperature and crystallinity of the alloy were characterized.The crystal structure and morphological evolution during the crystallization process are qualitatively investigated.The non-isothermal crystallization kinetics of the raw materials and the alloy are quantitatively analyzed.It has been shown that the two components in the PET/PA6 alloy crystallized separately and would not interfere with each other.The degree of crystallization of CDP raw materials is very low.However,in the CDP/PA6 alloy,the graft copolymer provided the nucleus for the crystallization of CDP,promoted the crystallization of CDP,and led to faster and more completed the crystallization of CDP.When the content of CDP and PA6 in the alloy were both 50%,the crystal diffraction peak of CDP is the sharpest.The crystallization temperature of PA6 increased with the increase of CDP content,but the melting point decreased.The study of non-isothermal crystallization kinetics reveals that the crystallization rate of CDP in the alloy is faster than that of the corresponding raw materials.With the increasing content of CDP in the alloy,the crystallization process of nylon changes from dominated homogeneous nucleation to mixed heterogeneous/homogeneous nucleation.It is found that the chain extender has little effect on the crystallization performance of the system.The thermal and mechanical properties of polyester/PA6 alloy are explored.The CDP/PA6 alloy has both the glass transition temperature of PA6 and CDP,and both glass transition temperatures increase with the increase of CDP content.When the two raw materials were added in the same amount,the glass transition temperature of the two components was the closest,which further shows that the compatibility is best at this composition.The thermal stability of the alloy is lower than that of the raw material CDP.However,the initial decomposition temperature of all CDP/PA6 alloy is above 340℃,which is much higher than the processing and application temperature of the material.PET/PA6 alloy is too brittle and does not have any practical value.When the content of PA6 is high,the mechanical properties of CDP/PA6 alloy are far better than CDP,and some parameter are better than PA6.After adding 30%CDP,the tensile strength of the alloy is increased by 50%and the elongation at break is increased by more than 10 times(400%),compared with that of PA6.Therefore CDP/PA6 alloy has the potential to become an engineering plastic.