Study On Multi-functional Topological Branching Modification Of Foaming PET

Polyethylene terephthalate（PET）is widely used in the fields of fibers,bottles and films due to its excellent physical properties.Owing excellent renewable performance,PET becomes one of the few materials having realized industrial cyclic regeneration.Therefore,the development of PET for foam packaging is of significant importance for improving express packaging pollution and reducing environmental pressure.However,conventional PET has low molecular weight and straight chain molecular structure,resulting in poor melt viscosity and melt elasticity,making it difficult to form complete bubble structures and foam materials.In this paper,multi-functional epoxy modified agents and multi-functional anhydride chain-extending agents were used to modify PET through topology branch chain extension via reactive melt extrusion.The effects of the two chain extender agents on PET rheology were systematically studied,and the foaming performance of modified PET was verified by chemical foaming method.The specific research contents are as follows:PET was modified by reactive extrusion using tetraglycidyl diamino diphenyl methane（TGDDM）and pyromellitic dianhydride（PMDA）separately,and the effects of chain extender types and contents on the melt rheology of PET were studied using a torque rheometer and a rotational rheometer.The results show that during the melt modifying process of PET in torque rheometer,the torque gradually increased to a peak value as the processing time increased,and then decreased with the extension of processing time.For PET modified with the same chain extender,the torque increased gradually with the increasing amount of chain extender while decreased with even higher chain extender content.The torque reached a maximum value at a content of 1.0%for either TGDDM or PMDA.Solubility analysis of modified samples shows that some gel at a TGDDM content of 0.7%or a PMDA content of 1.0%,indicating that the molecular chain of modified PET becomes crosslinking.Compared with PMDA modified PET,TGDDM modified PET shows a shorter reaction onset time and a higher torque peak value with the same amount of chain extender.Modified PET with TGDDM shows higher complex viscosity and storage modulus,indicating higher reaction rate.The modification effect of TGDDM combined with PMDA on PET was investigated by changing the mass ratio of the two chain extenders.The results show that when TGDDM and PMDA were used together for modification of PET,the gel content formed inside the modified PET is increased,but the complex viscosity and storage modulus of the melt decreased.When TGDDM is added at 1.0%and PMDA is added at various amounts for PET modification,TGDDM plays a main role while PMDA plays a supporting role during modifying PET.The addition of PMDA was beneficial for accelerating PET branching reaction.With increasing content of PMDA,the time of modified PET reaching its torque peak gradually shortened.But the reaching time becomes longer as PMDA content keep increasing.When adding 1.0%TGDDM and 0.1%PMDA,the torque of the modified PET is close to that without PMDA,but the time reaching torque peak is shortened by 1.7 min compared to T_1.0P₀.When adding 1.0%TGDDM and 1.2%PMDA,the time reaching torque peak is only shortened by 1.0 min compared with T_1.0P₀.Therefore,the combination of two chain extenders only increases the rate of branching reaction.The higher reaction rate is more suitable for twin screw extrusion modification,which provides a certain reference for industrial foaming modification of PET.The PET modified by TGDDM,PMDA,or PMDA/TGDDM combination was verified through melt foaming using the PET chemical foaming method.The effect of foaming process on modified PET foaming was explored by regulating foaming temperature,foaming time,and foaming agent content.The results show that the foaming performance of modified PET is closely related to its complex viscosity and storage modulus.According to the comparison of the rheological properties of original PET,T_1.0P₀ with high melt viscoelasticity and partial cross-linking structure is found obtaining PET foam materials with a stable cell structure and relatively uniform cell size.Its foaming ratio was recorded as 3.8,the average cell diameter was 98μm,and the foaming density was 2.49×10⁷ cell/cm³.This result is weaker than that of traditional olefin-based foaming materials,has been greatly improved compared with original PET.The foaming process also has different effects on the foaming properties of modified PET.Increasing foaming temperature or prolonging the foaming time will increase the cell size and foaming ratio.However,as the temperature continues to rise and the time continues to lengthen,the foaming cells would rupture.When the foaming agent content gradually increases,the cell diameter,cell density,and foaming rate all gradually increase.When the foaming agent content continues to increase,the cell diameter and foaming rate continue to rise,while the cell density decrease.