Effects of molding temperature, pressure and time on polyvinyl alcohol nanocomposites properties produced by freeze drying technique

•Development of the processing of cellulose nanocomposite by using freeze drying of CNF/PVA suspension.•The relationship between molding conditions and the characteristics was investigated.•Cox-Krenchel model showed a good fit for nanocomposites molded at low temperature and pressure.•Our method was low-cost, simple and fast to fabricate nanocomposites with more uniformly dispersed CNF. The main aim of this study was to develop a novel approach to incorporate high cellulose nanofiber (CNF) loadings into polyvinyl alcohol (PVA) nanocomposites. The nanocomposites were prepared by freezing via liquid nitrogen and consequent freeze drying combined with hot press molding. To investigate the effect of the molding parameters on the morphological, mechanical and thermal properties, chemical structure and transparency of the PVA + CNF nanocomposites, two different mold pressures, temperatures and holding times were used for fabrication of PVA + CNF nanocomposites. The maximum tensile strength of 121 MPa of the PVA + CNF 20% nanocomposites was obtained when they were molded at 130 °C and 50 kPa for 7 min. Dynamic mechanical analysis showed that the storage modulus of the composites prepared at 130 °C and 50 kPa for 7 min is about 20% higher than nanocomposites molded at 150 °C and 150 kPa for 10 min. Optical properties (absorption spectra) of the PVA and PVA + CNF nanocomposites were increased as the mold pressures, temperature and holding time increased. Micrographs showed more sough fracture surface with increasing pressure and temperature during hot press molding.