Study On Strong Toughening Treatment And Microfoaming Process Of The Recycled PETs

With the development of global economy and the improvement of people’s living standards,plastic products are occupying an increasing share in our daily lives.Polyethylene terephthalate(PET),due to its excellent properties such as high strength,scratch resistance,heavy pressure resistance,and good transparency,has become a widely used packaging material in industries like food,medicine,and cosmetics.However,with the increase of PET packaging waste,environmental pollution is becoming more and more severe.Therefore,recycling is regarded as an important method to reduce plastic waste.Currently,recycled PET(rPET)is mainly used for the production of regenerated materials.However,the poor mechanical and heat resistance properties of rPET have limited its reuse range.Improving the mechanical and heat resistance properties of rPET is essential to increase its recycling value and expand its application fields.Therefore,this paper will focus on the preparation of high strength,high heat resistance and high toughness rPET materials and the study of microcellular foaming technology,aiming to make certain contributions to the cause of environmental protection.Firstly,this paper presents a green process to achieve heat resistance enhancement of rPET by CO2 treatment at room temperature.The results showed that the crystallinity of rPET samples treated with CO2 at 800 psi increased by 30.6%,and the tensile strength and Young’s modulus increased by 21.9%and 20.6%,respectively,compared with the untreated samples.In addition,dynamic mechanical analysis showed that the heat resistance of the CO2-treated samples was significantly improved,with a 33.5%increase in storage modulus and a 17.7℃increase in glass transition temperature.In addition,to investigate the principle of CO2 treatment to improve the mechanical properties of rPET,adsorption-desorption experiments were conducted in this paper to investigate the kinetics of CO2 adsorption in rPET matrix,combined with the use of Avrami model to analyze the crystallization kinetics of rPET under high pressure CO2 conditions.It was shown that the improvement of rPET tensile and thermal properties was attributed to the transformation of the crystals from a two-dimensional to a threedimensional structure as the CO2 saturation pressure increased.Secondly,based on the concentration distribution of CO2 within the rPET matrix under different saturation conditions and the different crystallinity of rPET,structurally controllable foams were prepared using the batch foaming.The results showed that the presence of partially crystalline matrix led to the decrease of cell size and the increase of cell density by affecting the cell growth mechanism and the cell nucleation mechanism.Microcellular foams with cell sizes in the range of 20～200 μm and cell densities in the range of 106～109 cells/cm3 were obtained by changing the foaming process conditions.The effect of heat foaming on the properties of rPET materials was also investigated.The crystallinity of rPET increased significantly under the effect of high temperature and stretching during the foaming process.For example,the crystallinity of rPET samples induced at 500 psi saturation pressure was around 11%,while after foaming,the crystallinity of the material increased to 37%.Finally,the rPET/TPEE blends were prepared using melt blending,and the two-phase morphology was observed by SEM,and it was found that TPEE could be uniformly dispersed in the rPET matrix at a very small scale,but the two phases did not achieve complete miscibility.With the increase of TPEE content,the crystallinity of rPET/TPEE blends decreased and the toughness increased dramatically.When 30 wt%TPEE was added to the pure rPET,the elongation at break could be increased by about three times and the impact strength was increased by more than 50%.The rheological and dynamic mechanical properties of the blends were also analyzed and the rPET/TPEE blends were found to be easier to process than pure rPET.The rPET/TPEE microcellular foam was prepared by foaming the blends with different content ratios.It was found that the increase of TPEE content promoted the nucleation and foaming process and improved the cellular morphology.