Largely improved toughness of polypropylene/long glass fiber composites by β-modification and annealing

β-Modification and annealing were adopted to improve the impact strength of long glass fiber reinforced (LFPP) composites. It was found that either β-modification or annealing is an efficient way to toughen LFPP composites, and largely enhanced impact toughness can be achieved via simultaneously using β-modification and annealing, particularly for the toughness at low temperatures (−40 °C to −20 °C). Meanwhile, the tensile strength and Young’s modulus of the composites could be maintained. Various characterizations were used to understand the microstructure changes and toughening mechanism after β-modification and annealing. The results show that the higher extent of the matrix plastic deformation could be the main reason for the enhanced toughness as induced by β-modification and annealing. The possible structural origins for the higher extent of matrix plastic deformation are also discussed.