Void content of polypropylene/carbon fiber wet‐laid nonwoven composites: Effect of fiber content and molding conditions, and void elimination mechanism

Abstract Various wet‐laid nonwoven composites have been well‐developed in recent decades. However, studies that systematically investigate the factors affecting the void content of wet‐laid nonwoven composites are still missing. This paper aims to study the factors affecting the void content of wet‐laid nonwoven composites and propose a mechanism for void elimination in wet‐laid nonwoven composites. Polypropylene (PP) and carbon fiber (CF) were chosen to manufacture PP/CF wet‐laid nonwoven composites. An orthogonal experimental design found that the CF content and molding pressure can dominate the void content while molding temperature and time have non‐significant effects. Subsequently, this paper proposed that the void elimination mechanism is the compression of the impregnated CF network and the trapped air (compression mechanism) instead of the matrix's infiltration to the dry CF network (infiltration mechanism). In order to validate the compression mechanism, we developed an analytical model for predicting the void content of the PP/CF wet‐laid nonwoven composites. Good agreement between the predicted and the experimental void content suggests that void elimination follows the compression mechanism. Highlights An orthogonal experimental design reveals that the CF content and molding pressure can dominate the void content of the PP/CF wet‐laid nonwoven composite, while molding temperature and time have non‐significant effects. A mechanism (i.e., compression mechanism) is proposed to explain the effect of CF content and molding conditions on the void content of the PP/CF wet‐laid nonwoven composite. Good agreement between the experimental and the predicted void content validates the compression mechanism.