Fiber–matrix interface of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) biocomposites with green-treated Agave americana fibers: new insights from viscoelastic behavior and Weibull analysis

Natural fibers present several challenges when incorporated as reinforcing fillers in biocomposites. Indeed, hydroxyl groups present on their surface cause moisture-induced swelling, thus weakening interfacial interactions. Therefore, chemical treatments are crucial for reducing fiber hydrophilicity. In this work, the objective is to investigate the effect of two eco-friendly treatments, i.e. citric acid and sodium bicarbonate, on the crystallinity and tensile properties of Agave Americana fibers (AAF). Both untreated and treated fibers are incorporated in PHBHHx at 30 wt.%. The fiber surface modification efficiency on the biocomposite properties is evaluated by viscoelastic behavior at the fiber–matrix interface. XRD data show an increase in crystalline index (CrI) of bicarbonate-treated fibers (AAF-B), whereas it slightly decreases for those treated with citric acid (AAF-A), likely due to esterification reactions. Tensile tests on fiber bundles exhibit improved tensile modulus for AAF-B. Moreover, the Weibull analysis indicates that the changes in tensile properties are undoubtedly due to surface treatments, whatever the values of the standard deviation. On the other hand, the theoretical storage modulus and (B) parameter, designed as an interfacial strength indicator of PHBHHx/AAF, show improved interfacial adhesion strength for both treated biocomposites, being, however, more pronounced for the AAF-B sample.