Second Component Induces Microstucture Changes In The Annealed Polypropylene And The Corresponding Mechanical Properties

Polypropylene has good physical and chemical properties:relatively low density (about0.9g/cm3), good tensile strength, bend strength and compress strength and excellent bending fatigue resistance; low water absorption; acid and alkali corrosion resistance. Furthermore, it can be applied above100℃for a long time. However, PP exhibits poor impact toughness, especially at low temperature. Therefore, the research for toughening PP has been a hot subject for recent years. Generally, chemical and physical modifications are applied for toughening. Physical modification is the most simple and effective method, including organic rigid particle toughening PP, inorganic rigid particle toughening PP, rubber toughening PP, core-shell particle toughening PP and so on. When organic and inorganic rigid particles are used to toughen PP, the stiffness and strength of PP increase to a certain degree, but the obvious toughening effect is hardly to be achievecould; while, in terms of rubber toughening PP, although the toughness of PP can be increased obviously, the material exhibits dramatically decreased stiffness and strength.In order to toughening PP without sacrificing the stiffness and strength, annealing treatment was uesed. Isotactic Polypropylene (iPP), Polypropylene random copolymer (PPR) and Impact-resistant polypropylene copolymer (IPC) were studied in this paper. Bis(2-ethylhexyl) adipate (DOA) and Octylphenol polyoxyethylene ether (trade name of OP-10) were added into iPP to prepare iPP/DOA and iPP/OP-10samples, respectively. What’s more, copolymerizing polypropylenes with the second component (PPR and IPC). which were obtained through in situ polymerization, were directly studied. The micro-structure and mechanical response of the system could be adjusted by annealing treatment, and the toughening mechanisms of annealing PP were studied subsequently. Main conclusions were obtained as follows:(1) iPP/DOA samples were obtained by adding5wt%plasticizer DOA into iPP. The plasticizing effect of DOA increased the chain segments mobility of iPP/DOA-23and iPP/DOA-140samples, namely, the chain mobility of iPP/DOA-23and iPP/DOA-140samples were better than iPP-23and iPP-140samples, respectively. The mechanical property measurements showed that the plasticizer DOA and annealing treatment had synergistic effect in improving the impact toughness of PP. This proved further the important role of chain segments mobility in toughening PP materials.(2) iPP/OP-10samples with different OP-10contents (0.5-2wt) were obtained by adding different OP-10. Microvoids could surely induce into iPP matrix by adding OP-10. With the increase of OP-10content, the number of microvoids increased accordingly. After annealing treatment, the amount of microvoids of iPP/DOA samples further increased, and chain segments mobility of matrix also incresed. Although OP-10didn’t have an obvious influence on matrix chain segments mobility and crystallization behavior, the existence of numerous microvoids further increased the deformation ability of annealed samples.(3) The influences of annealing temperature and annealing time on microstructure and mechanical properties of PPR were investigated. Results showed that annealing treatment induced amorphous chain segments rearranging into lattices, which led to slightly increased crystallinity and integrated crystalline structure, looser amorphous region and inceased chain segments mobility. The inceased chain segments mobility is the cause of increased impact toughness of samples. The highest impact strength of the PPR-100sample demonstrated that the optimizing annealing temperature for PPR was100℃, which was lower than that for annealed iPP. In addition, the microstructure rearrangement of PPR finished within3h in the condition of100℃. This demonstrated that the existence of ethane monomer could promote the accomplishment of chain rearrangement at relatively lower annealing temperature and/or within reltively shorter annealing duration.(4) IPC with multiple-phase structure was annealed under different temperatures. The results showed that, annelaing treatment enhanced the chain segments mobility of iPP matrix, which promoted the plastic deformation of IPC samples under the external force on the one hand. On the other hand, annealing treatment induced more homogeneously distributed rubber phase, which facilitated the overlap of stress filed around rubber particles. Consequently, the plastic deformation of PP matrix was also enhanced. What’s more, the concealed structure of rubber transformed into core-shell structure after annealing. The improved microstructure endowed the annealed IPC material with excellent fracture toughness, especially at relatively low temperature.