Tensile Strength of Poly(lactic acid)/Bleached Short Hemp Fiber Fully Green Composites as Replacement for Polypropylene/Glass Fiber

Abstract

The compatibility between poly(lactic acid) (PLA) and natural fibers to develop bio-sourced, recyclable, and biodegradable composites remains a commonplace issue. This work highlights that, at least in the case of hemp, pulping and bleaching towards delignified short fibers attained remarkable improvements over untreated hemp strands. This approach differs from usual proposals of chemically modifying hydroxyl groups. Soda-bleached hemp fibers (SBHFs) granted a relatively large bonding surface area and a satisfactory quality of the interphase, even in the absence of any dispersant or compatibilizer. To attain satisfactory dispersion, the matrix and the fibers were subjected to kinetic mixing and to a moderately intensified extrusion process. Then, dog-bone specimens were prepared by injection molding. Up to a fiber content of 30 wt.%, the tensile strength increased linearly with the volume fraction of the dispersed phase. It reached a maximum value of 77.8 MPa, signifying a relative enhancement of about 52%. In comparison, the tensile strength for PLA/hemp strands was 55.7 MPa. Thence, based on the modified rule of mixtures and the Kelly & Tyson modified equation, we analyzed this performance at the level of the constituent materials. The interfacial shear strength (over 28 MPa) and other micromechanical parameters were computed. Overall, this biocomposite was found to outperform a polypropylene/sized glass fiber composite (without coupling agent) in terms of tensile strength, while fulfilling the principles of green chemistry.

Avocado Pruning Residues for the Formulation of Bio‐Based Polyethylene/Fiber‐Based Biocomposites for Sustainable Food Packaging

“…These values are far from the properties of fibers like Hemp, which have an intrinsic strength of over 800 MPa. [ 73 ] Additionally, we found that the 30% composition exhibited a stronger interface. Therefore, while avocado fibers can reinforce the bio polyethylene matrix, they do not lead to significant increases in tensile strength.…”

Comparative Study on the Stiffness of Poly(lactic acid) Reinforced with Untreated and Bleached Hemp Fibers

“…Hence, the loss of cellulose was as high as 32% over the initial weight of hemp, which puts the convenience of pulping and bleaching for stiffness-limited design under question. Nonetheless, they have been proven to be of utmost relevance to enhance the tensile strength, for which the quality of the interphase has a significant influence [19]. On one hand, the removal of amorphous components (lignin, some hemicellulose macromolecules, and extractives) is generally expected to impart greater intrinsic stiffness [39].…”

“…Furthermore, the possible gains attained by removing amorphous components were plausibly hampered by the depolymerization of cellulose during alkaline pulping and bleaching [41]. In the same sense, these treatments damaged the surface of fiber hemps to the point of generating a high amount of fines (47%), which may contribute to the tensile strength of the material [19,42], but made no significant contribution to stiffness.…”

“…Nonetheless, this practice does not comply with the principles of green chemistry [18]. Well-known and relatively clean processes, such as soda pulping and total chlorine bleaching, have been shown to enhance the tensile strength of PLA/hemp composites [19], but at the expense of significant material losses.…”

Circular Production, Designing, and Mechanical Testing of Polypropylene-Based Reinforced Composite Materials: Statistical Analysis for Potential Automotive and Nuclear Applications

“…and fast curing [ 89 ]. PP-sisal [ 90 ], PP-wood fibers [ 91 ], PP-hemp + glass fibers [ 92 ], and PP-nylon [ 93 ] are common examples of fabrication of composite materials. After development of composite materials, the quality and performance are inspected using thermal analysis, tensile, bend, impact, abrasive, and erosive testing for commercial applications [ 94 , 95 , 96 , 97 , 98 ].…”