Freeze dried cellulose nanocrystal reinforced unsaturated polyester composites: challenges and potential

Functionalized cellulose particles were studied as a potential reinforcement for an unsaturated polyester resin (UPR) system, a common material for automotive applications of fiber reinforced plastics. A preliminary process for incorporating freeze-dried cellulose nanocrystal (CNC) powder into UPR was developed. Three surface chemistries were explored including sulfonated, methyl(triphenyl) phosphonium (PhCNC), and maleic acid (MCNC). By optical microscopy the filler was seen to be agglomerated within the matrix. Fractography showed that these agglomerates acted as stress concentration points resulting in decreased tensile and flexural strength. With the addition of 1wt% CNCs, the flexural and tensile modulus increased by up to 53% and 22%, respectively. Dynamic mechanical analysis indicated that the PhCNC- and MCNC-UPR samples had a 61% and 66% higher glassy modulus than neat UPR, respectively. Despite the lack of nano-scale dispersion of CNC in UPR, these results reflect potential in the use of functionalized CNC agglomerates as an additive in UPR systems to produce composites with high moduli and good thermo-mechanical stability.