Influence of interface strength gradation on mechanical properties of woven glass fabric/polypropylene laminates

Recently, thermoplastic polymer composites have gained a growing interest owing to many advantages with respect to thermosets based ones as shorter processing times, improved fracture toughness and potential recyclability. However, their potentialities are still restricted by some drawbacks mainly related to the high cost of matrices and the relatively poor know-how in terms of design and manufacturing. For example, a huge amount of studies are available about approaches to improve the damage tolerance of composite laminates based on thermosetting matrices but, at present, a relevant lack of know-how on the same topic for thermoplastic systems limits their perspectives especially for structural applications. Aside from conventional hybridization approaches, a new class of hybrid laminates were realized by grading the interlaminar polymer/fibres interface strength (IGIS). Composites were prepared by alternating glass woven fabrics with polypropylene (PP) layers, either neat and compatibilized for glass fibres by using a maleic anhydride grafted PP. Different sequences were investigated and compared by flexural and low-velocity impact tests with not graded laminates (i.e. containing only neat or compatibilized PP layers as matrix). Results demonstrated that the IGIS design allows to prepare composites with high flexural properties coupled with high impact resistance at the same time, without affecting the reinforcement configuration nor using fibre hybridization methods.