Synthesis And Properties Of Polystyrene/PPTA Nanocomposites

As one of the five general plastics,Polystyrene（PS）has been widely used in various fields of modern society.Its structure is dominated by saturated hydrocarbon chain,side chain is rigid benzene ring structure,so it has superior physical and chemical properties such as high transparency,high rigidity,acid and alkali resistance,easy molding,low cost and so on.However,the existence of side phenyl causes the instability of theαhydrogen atoms on the main chain,which is more easily activated by the oxygen in the air and oxidized into oxides,leading to the degradation of the polymer and the reduction of molecular weight.Therefore,it has many shortcomings such as poor impact resistance,easy embrittlement,low thermal deformation temperature and so on.Para-aramid fiber（PPTA）is a high performance man-made fiber.Due to its structure with intermolecular hydrogen bonds and highly extended rigid chains,PPTA has high crystallinity and crystal orientation,which gives it unique material properties,such as high strength,high modulus,good chemistry and flame retardant,etc.Therefore,PPTA is generally considered as an ideal reinforcing material.However,PPTA also has some shortcomings,such as low chemical reactivity,poor dispersion performance of solution,smooth surface,weak bonding strength of interface and so on.In this paper,aramid nanomaterials（ANM）was prepared by nano PPTA as the strengthening material of polystyrene.PS/PPTA nanocomposites were prepared by two different synthesis strategies:―top-down‖and―bottom-up‖.ANM,to a certain extent,has the dual advantages of both macroscopic PPTA and nanomaterials,showing high strength,large specific surface area,many active groups and so on.This study not only overcomes the disadvantages of PPTA but also enhances the properties of polystyrene.The main research contents are as follows:1、Adopt―top-down‖strategy.Firstly,PPTA was dissolved into DMSO/KOH solution,and the dispersion solution of aramid nanofibers（ANFs）was obtained by deprotonation of amide groups.Then,the ANFs were modified with allyl and benzyl,and the modified R-ANM was added into the PS matrix as the reinforcing material.Finally,a series of R-ANM/PS nanocomposites with different substitution degrees were prepared,which broke through the limitation that the application of PPTA is mostly limited to those polymers containing-OH or-NH₂ groups.2、Adopt―bottom-up‖strategy.Monomer p-phenylenediamine（PPD）and p-benzoyl chloride（TPC）are directly added to polystyrene matrix to obtain ANM by in-place condensation.The nanocomposites of ANM/PS and ANM/HIPS were obtained successfully.Compared with―top-down‖method,this method not only has simple operation and short time,but also avoids agglomeration of nanoparticles in solvent and poor compatibility with matrix more effectively.3、The structure and morphology of R-ANM/PS,ANM/PS and ANM/HIPS nanocomposites were characterized.The successful synthesis of PPTA was verified by infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.Transmission electron microscopy（TEM）images showed that different morphologies of ANMs were observed with different system concentrations,and different forms of ANMs could be evenly dispersed in PS matrix without undesirable agglomeration.The surface,fracture section and surface roughness of the composites were analyzed by scanning electron microscopy（SEM）and atomic force microscopy（AFM）.It can be seen that the roughness of nanocomposites increases with the increase of monomer content.The fracture section also gradually changed from brittle fracture to ductile fracture.In addition,the thermal stability and mechanical properties of R-ANM/PS,ANM/PS and ANM/HIPS composites were tested.The results show that the thermal stability and mechanical properties of R-ANM/PS,ANM/PS and ANM/HIPS nanocomposites are greatly improved compared with pure polystyrene materials.Mechanical property test results show that:（1）regardless of the modification of ANM by allyl or benzyl,the toughness of R-ANM/PS materials increases most significantly when the substitution degree is 50%,but there is no significant difference in the enhancement degree of yield strength and toughness when the substitution degree is 100%and 200%.（2）The mechanical properties of ANM/PS-5composites are improved most significantly,with Young’s modulus and toughness reaching 1652.22MPa and 0.84N/mm².（3）Compared with pure HIPS,Young’s modulus of ANM/HIPS nanocomposites increased from 246.55MPa to 2025.12MPa with a maximum increase of 721%.The tensile strength of ANM/HIPS increased from3.07MPa to 29.76MPa,and the increase rate was 869%compared with that of pure HIPS.Toughness maximum increased by 1125%,from 0.32N/mm² to 3.92N/mm².The increase of mechanical properties may be related to the content and morphology of PPTA nanomaterials in the matrix.This paper provides a new approach to solve the problems of PPTA nanomaterials in matrix,such as easy aggregation,difficult dispersion and interaction with matrix.At the same time,it is of positive significance to endow PS with special excellent properties and broaden its application field.