Mechanical Properties of Hybrid Natural Fiber–Carbon Fiber‐Reinforced Polypropylene Nonwoven Composites: Influence of Degree of Densification, Fiber Volume Fraction and Laminate Architecture

Abstract

Nonwoven composites based on flax fiber (NF)‐reinforced polypropylene (PP) offer a promising route toward sustainable lightweight structures but are limited by moderate mechanical performance. In this work, a hybridization concept employing carbon fiber (CF) nonwoven surface plies with varying volume content is investigated. Hybrid NF–CF–PP composites were manufactured by compression molding and systematically evaluated with respect to densification degree, carbon fiber volume fraction, and laminate architecture. The results demonstrate that densification degree is the dominant parameter governing mechanical performance. Increasing molding pressure significantly reduces void content and leads to pronounced improvements in flexural and tensile properties. Symmetric CF surface reinforcement with low areal weight (200 g/m 2 per ply) effectively increases stiffness and strength, with optimal performance achieved at approximately 30 vol% CF. Higher CF contents do not yield further improvements, owing to insufficient impregnation and increased void formation, as found during preliminary tests. Graded laminate architectures do not provide a measurable advantage over homogeneous CF distributions for flat‐plate geometries. Impact performance, similarly, is governed by densification rather than hybridization. Contrary to expectations, they did not outperform homogeneous surface reinforcement, underscoring densification as the dominant design parameter. The findings provide clear design guidelines for load‐adapted hybrid nonwoven composites manufactured by industrial compression molding and form the basis for load‐bearing nonwoven molded parts with variable surface weight.