Preparation And Properties Of Nanocellulose Whiskers/Chitosan Biodegradable Composite Packaging Films

There is a growing interest in making plastics that are based on natural renewable materials. As one of those, Chitosan(CS) has been found to be non-toxic, biodegradable, biocompatible and was reported by several researchers to have strong antimicrobial and antifungal activities. However, the use of CS has been limited because of its inherent poor mechanical and water-resistant properties. Polymer blending is one of the effective methods for providing CS for a variety of applications. In this paper, we choose highly crystalline cellulose particles called nanocellulose whiskers (NCW) as the reinforcement. NCW has advantages over other organic or inorganic fillers, not only due to improving drawbacks of CS, but also remaining its biodegradability and other good advantages.Firstly, NCW were isolated from microcrystalline cellulose (MCC) via acid hydrolysis, and then composite films were prepared via solution casting technique. Films were all characterized by SEM, FTIR, and XRD to determine their cross section surfaces, molecular groups and crystallizations in the following. A series of tests were performed at last for trying to find the relations between micro-structure and macro-properties. The main contents and conclusions of this paper were as follows:1. The diameter of NCW determined based on AFM was 5～20nm and the length was 100～500nm with aspect ratio about 30. XRD patterns of NCW indicated that the crystal integrity of cellulose had been maintained during the hydrolysis process. The degree of crystallinity of NCW increased from 63% to 68% showed that the hydrolysis occurred in the amorphous regions. FT-IR spectra also showed the molecule of NCW had all typical peaks of cellulosic structure.2. SEM images of cross sections exhibited a good dispersion at less percentage of NCW. The electrostatic and hydrogen bonds can be found to form a rigid reinforced cross-linking network through FT-IR. From the XRD patterns of composite films, the addition of NCW influences the crystallinity of CS when solution casting.3. Composite films under dry, wet and plasticized conditons were tested for their mechanical performance. With increasing NCW content, the tensile strength significantly increased from 51.4 to 80MPa, 15.5 to 25.1MPa and 29.4 to 62.8MPa respectively. Meanwhile, tensile modulus of films grew linearly. Polyethlene-glycol (PEG) 400 dramatically improved plasticity. The breaking elongation reached above 25%, while strength maintained at a highest level.4. DMA revealed multiple increasement on storage modulus in all temperature range and glass transition temperature shifted to higher. Water uptake decreased dramaticly at equilibrium in the presence of NCW which showed an improved water resistance. Besides NCW had helped to improve barrier and thermal properties of CS films, the composite films kept a high degree of transparency.