Study On Impact Resistance Improvement-oriented Preparation Process Of Long Glass Fiber Reinforced Polypropylene Composites

As common lightweight materials for automobiles,long glass fiber reinforced random copolymer polypropylene composites are commonly used in structural components of automobiles due to their high specific strength,low cost and recyclability.Since these structural components often face impact damage,it is of vital signicance to toughen these composites.Modification of the matrix is a common method to enhance the impact performance of polymers and their composites,and research from the matrix perspective plays a very important role in the toughening of composites.In this study,the LGF/PPR/MPPR composites were effectively toughened by addingβ-nucleating agent to modulate the crystallization behavior and and change the crystal structure of the matrix,and the impact strength of the composites was further improved by optimized annealing process.This study will be carried out and conclusions will be drawn according to the following work:(1)The effect ofβ-nucleating agent content on the crystallization behavior of the composites was analyzed,and crystallization kinetic model was established based on the crystallization curves to analyze the changes of crystallization parameters.The results showed that the addition ofβ-nucleating agent at an appropriate concentration(0.1wt%)could increase the crystallization temperature of LGF/MPPR/PPR composites by 5.0°C and reduce the semi-crystallization time by 16.3%.Meanwhile,the Friedmann equation revealed thatβ-nucleating agent significantly reduced the crystallization activation energy of the composites,indicating that the addition ofβ-NA reduced the energy barrier required for the crystallization of the composites.The melting curve results showed thatβ-nucleating agent successfully induced the generation ofβ-crystals with a relative content K_βof 45%at 0.1 wt%.(2)The effect ofβ-nucleating agent content on the mechanical properties of the composites was analyzed,and the toughening mechanism was revealed from the perspectives of both crystallinity and crystalline phase composition.β-nucleating agent induced the generation ofβ-crystals through heterogeneous nucleation,and the phase content ofβ-crystals was elevated to 50%at an appropriate amount ofβ-nucleating agent content(0.1wt%),which led to a 26.3%increase in the impact strength of the composites.Further elevation ofβ-nucleating agent concentration will lead to the change ofβ-crystal shape and thus reduce the impact strength,so the amount ofβ-nucleating agent addition must be controlled reasonably.(3)The effects of annealing temperature on the crystalline phase content as well as the crystal structure of the composites were analyzed,and the enhancement mechanism of the mechanical properties of the composites after annealing was analyzed from the aspect of both crystalline and amorphous phase.The results showed that the crystallinity of composites increased by 7.5%at the suitable annealing temperature(130°C)due to the promotion of crystal rearrangement led by annealing.Annealing also affected the amorphous zone,as annealing rendered chain segments in amorphous zone rearrange,expanded the thickness of the amorphous zone,increase the chain segment activity,and lowered the glass transition temperature by 2.1°C.The dual effect significantly improved the tensile strength(11.6%improvement)and impact strength(18.3%improvement)of the composites.However,continuing to increase the annealing temperature will result inβ-αrecrystallization,leading to a significant decrease in impact strength.