The surface modification of cellulose nanocrystals (CNC) is a key intermediate step in the development of new functionalities and the tailoring of nanomaterial properties for specific applications. In the area of polymeric nanocomposites, apart from good interfacial adhesion, the high thermal stability of cellulose nanomaterial is vitally required for the stable processing and improvement of material properties. In this respect, the heterogeneous esterification of CNC with succinic anhydride was investigated in this work in order to obtain CNC with optimised surface and thermal properties. The influence of reaction parameters, such as time, temperature, and molar ratio of reagents, on the structure, morphology and thermal properties, were systematically studied over a wide range of values by DLS, FTIR, XPS, WAXD, SEM and TGA methods. It was found that the degree of surface substitution of CNC increased with the molar ratio of succinic anhydride to cellulose hydroxyl groups (SA:OH), as well as the reaction time, whilst the temperature of reaction showed a moderate effect on the degree of esterification in the range of 70–110 °C. The studies on the thermal stability of modified nanoparticles indicated that there is a critical extent of surface esterification below which only a slight decrease of the initial temperature of degradation was observed in pyrolytic and oxidative atmospheres. A significant reduction of CNC thermal stability was observed only for the longest reaction time (240 min) and the highest molar ratio of SA:OH. This illustrates the possibility of manufacturing thermally stable, succinylated, CNC by controlling the reaction conditions and the degree of esterification.

The wider use of renewable feedstock in structural applications, where high mechanical performance is required, can be achieved by the application of recently developed engineering biopolymers and their further modification by micro- and nanoparticles. In this review, we present the current state of the art of biopolyamide materials for structural and functional applications. The overview includes all stages of the manufacturing—from the synthesis of building blocks, through the synthesis of polymers and its physical modification, with special emphasis on the properties of the obtained engineering biocomposites as a final product of modern polymer technology. In the first part, the synthetic routes of bio-derived counterparts of common polyamides as well as specialty polymers with functional properties arising from the complex structure of biochemicals were exemplified. The development of environmentally friendly composites and nanocomposites based on biopolyamides and natural fillers, such as plant fibers or cellulosic nanofibers, was of particular interest due to preserved sustainable character of such materials.

Novel bio-polyamides obtained from renewable resources, e.g. PA4.10, are considered nowadays as promising ‘green’ engineering materials consisting of building blocks derived from castor oil. In this work the composites of heterogeneously acetylated microfibrillated cellulose (MFC) and biopolyamide 4.10 have been prepared by melt blending. Thermoplastic processing of PA4.10/MFC composites was possible in a narrow temperature window due to significant improvement of thermal stability of acetylated MFC as compared to raw MFC. The increase of thermooxidative stability of filler was due to removal of non-cellulosic components from the raw material and introduction of acetic moieties that had additional slight stabilizing effect on MFC. Moreover, the modified MFC showed significant changes in morphology that favoured its dispersibility in viscous polymer melt. Combined treatment of MFC by chemical agents, which caused partial hydrolysis of amorphous regions, and physical disintegration by ultrasonic waves resulted in formation of fibrous material with low degree of entanglement and submicron or nanometric diameters. In the tested range of screw speeds it was found that at screw speed of 100 rpm the shearing forces were sufficient for dispersing MFC agglomerates and the melt pressure secured evacuation of gases introduced to plasticizing system of extruder with MFC-Ac aerogel. The dynamic mechanical properties of obtained (nano)composites were influenced by both mechanical strengthening of rigid cellulose micro and nanofibers as well as susceptibility of biopolymers towards oxidation and thermomechanical degradation during processing.