Solvent-Cast PCL/Hemp Biocomposites: Screening of the Effects of Matrix Grade, Filler Content and Particle Size

Biodegradable poly(ε-caprolactone) (PCL)/hemp biocomposites were prepared by solvent casting in acetic acid to screen the effects of matrix grade, filler content, and particle size on tensile behavior. Two PCL grades (Capa® 6500 and 6800) were combined with milled hemp sieved at four sizes (0.08 to 1.0 mm) and two contents (20 and 30 wt%), giving 13 formulations (86 specimens), analyzed statistically and with a combined Pukanszky–Weibull model. Particle size produced a plateau: the 0.08 and 0.25 mm fractions were equivalent (padj > 0.25), with a marked drop at 0.5 mm. Raising the content to 30 wt% lowered the strength 2.5 to 4 times (p < 0.001), showing that hemp acts mainly as a filler. For PCL 6800 at 20 wt%, the modulus at the two finest sizes exceeded the neat value, a mild reinforcement described by a Halpin–Tsai term. A low Weibull modulus (mW ≈ 3) indicated defect-controlled behavior, and electron microscopy showed matrix voids, more pronounced for PCL 6800, and interfacial gaps. Thermal analyses indicated limited matrix degradation during dissolution and unchanged thermal stability. PCL 6800 with 20 wt% hemp at 0.25 mm performed best. This feasibility screening supports formulation selection for a planned melt processing phase.