Effect of cellulose and lignin content on the mechanical properties and drop-weight impact damage of injection-molded polypropylene-flax and -pine fiber composites

Abstract

Designing bio-composites for structural applications requires a thorough understanding of their mechanical behavior. In this study, we examined the differences in the tensile strength and drop-weight impact response between polypropylene reinforced with flax fibers and that reinforced with pinewood short fibers, as both fibers differ in composition (cellulose, hemicellulose, and lignin) and length-to-diameter ratio. We found that flax fibers, which have higher cellulose content and are twice as long as pine fibers, increased the stiffness and shock resistance of bio-composite materials. However, pine fibers, which contain more lignin, showed increased material ductility and energy absorption. Impulse excitation, acoustic emission and micro-CT techniques were used to evaluate the post-impact mechanical properties and the contribution of each damage mechanism to the final material failure (tearing). The experimental results were used to validate a model based on finite elements. Our results revealed that the experimental and finite-element analyses were in good agreement.

Effects of Lignin on the Thermal and Morphological Properties and Damages Mechanisms after UV Irradiation of Polypropylene Biocomposites Reinforced with Flax and Pine Fibres: Acoustic Emission Analysis

“…The chemical composition of flax fibre was primarily dominated by cellulose (68.7-75.5%), followed by hemicellulose (12.2-14%) and lignin (2.1-4.7%). In contrast, the chemical composition of pine fibre comprised 42% cellulose, 29% hemicellulose, and 28% lignin [8,13]. The peak observed at 460-464°C corresponded to the thermal degradation of PP.…”

“…Before each test, three pencil lead break tests were conducted to calibrate the source location of AE events and assess the coupling state between the specimen and the sensors. We analyzed the recorded AE acoustic signals analyzed, considering parameters such as amplitude, count, duration, and frequency, as referenced in [6,13,15]. Utilizing the K-means clustering algorithm, we assigned each set of acoustic events to a specific damage mechanism.…”

“…Flax boasts a substantial cellulose content, whereas pine fibres showcase distinct morphological features, unlike flax fibres, which are characterized notably by a high lignin content (28% contrasted with ~3% for flax [10,11]). Cellulose and hemicellulose modulate the yield strength and rigidity of biocomposites, while the hydrophobic nature of lignin acts as a binding agent for other components within natural fibres [10][11][12][13].…”

Artificial Neural Network Approach for Assessing Mechanical Properties and Impact Performance of Natural-Fiber Composites Exposed to UV Radiation

“…They are widely used in various industries, including construction, automotive, and packaging [ 3 , 4 ]. SNFT biocomposites offer high-specific mechanical properties and are eco-friendly [ 5 , 6 , 7 , 8 ]. Nevertheless, one major challenge in developing natural-fiber composites is their response to environmental factors, such as moisture, ultraviolet (UV) radiation, and heat, which can degrade their mechanical performance and limit their applicability, especially for outdoor applications [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ].…”

“…While most studies on the impact of environmental factors on composites focus on the loss of mechanical properties using quasi-static tests, such as traction and flexion [ 23 , 24 , 25 ], it is important to note that these structures also experience low-speed impacts. Unfortunately, few studies have explored the behavior of biocomposites in response to such impacts [ 7 ].…”