Cellulose-based composites physical properties

Richardson, M.J., Johnston, J.H., Borrmann, T., 2006. Electronic properties of intrinsically conducting polymer-cellulose based composites. Current Applied Physics 6, 462—465. 

Dall Acqua et al.45 reported the development of conductive fibres made by cellulose-based fibres embedded with polypyrrole. Several efforts with cotton, viscose, cupro and lyonell have followed. The conductivity is directly related to the amount of polypyrrole, oxidant ratio and fibre structure with significant differences between viscose and lyonell. Polymerisation occurs uniformly inside the fibre bulk, by producing a coherent composite polypyrrole/cellulose. The mechanical and physical properties of cellulose fibres were not significantly modified as they are the best available45. 

As is well established, polymer/polymer blending is an important method to improve the original physical properties of one or both of the components, or to obtain new polymeric materials showing widely variable properties without parallel in homopolymers. There have been numerous blend studies for various polymer pairs from both the fundamental and practical viewpoints. A few reviews [7,42] have described a general scheme for preparation and characterization of the blends and micro composites of unmodified cellulose with synthetic polymers, mainly based on works performed until 1994. The present review will cover the articles published on this topic since the mid 1990s, with extensions to related works on cellulose derivatives and other natural polysaccharides. 

In this chapter we have reviewed some of the most important characteristics of cellulose and cellulose based blends, composites and nanocomposites. The intrinsic properties of cellulose such as its remarkable mechanical properties have promoted its use as a reinforcement material for different composites. It has been showed that cellulose is a material with a defined hierarchy that tends to form fibrillar elements such as elementary fibrils, micro fibrils, and macro fibers. Physical and chemical processes allow us to obtain different scale cellulose reinforcements. Macro fibers, such as lignocellulosic fibers of sisal, jute, cabuya, etc. are used for the production of composites, whereas nano-sized fibers, such as whiskers or bacterial cellulose fibers are used to produce nanocomposites. Given that cellulose can be used to obtain macro- and nano-reinforcements, it can be used as raw material for the production of several composites and nanocomposites with many different applications. The understanding of the characteristics and properties of cellulose is important for the development of novel composites and nanocomposites with new applications. 

Also discussed in this chapter are the influence of other chemical treatments on the physical and mechanical properties of cellulose-based materials andthe effect of nanoclay on the morphological and mechanical properties of polymer composite. 

Cellulose-based natural fiber can be oxidized using oxidizing agent with acidic catalyst. Oxidation reactions applied to cellulose in fiber for chemical modifications [43]. Oxidation reactions occur on cellulose selectively at particular position. The reaction of sodium metaperiodate with cellulose in wood fiber in the presence of sulfuric acid catalyst at 120°C and 85 KPa pressure yielded the oxidized product. Sodium metaperiodate reacts with hydroxyl groups of cellulose and produce 2,3-dialdehyde cellulose which improved the physical and mechanical properties of polymer composites [44]. 

All polymer composites absorb substantial amounts of moisture or water in humid environment as well as in water. The most important concern in indoor and outdoor applications of natural fiber-based biocomposites with polymer matrices is their sensitivity to water absorption, which can reduce considerably their mechanical, physical, and thermal properties and performances. The water absorption of biocomposites results in the debonding or gap in the natural fiber-polymer matrix interfacial region, leading to poor stress transfer efficiency from the matrix to the fiber and reduced mechanical and dimensional stabilities as well [158]. It has been known that the hemiceUulose component in cellulose-based natural fibers may be mainly responsible for water absorption because it is more susceptible to water molecules than the crystalline cellulose component. Also, poor interfacial adhesion... 

Nakagaito, A.N., Yano, H., 2004. The effect of morphological changes from pulp fiber towards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites. Applied Physics A—Materials Science Processing 78, 547—552. 

---