Surface Modification of Nanocellulose

Solvent casting process is the simplest method for laboratory-scale preparation of PLA/nanocellulose biocomposites. Organic solvents for PLA dissolution such as N,N-dimethylacetamide (DMAc), 26,27,29,32,43,50,51,53,60-63 

The most suitable and practical manufacturing methods of nanocellulose reinforced thermoplastic composites for industrial applications are melt processing techniques. Nanocelluloses including unmodified and chemical modified CNFs and CNCs have been successfully melt blended or compounded with PLA by using an extruder - ° or melting 

In order to prepare PLA nanocomposites with highly dispersed cellulose nanocrystals and porous PLA-based scaffolds with enhanced mechanical properties and thermal stability, CNCs have been incorporated into PLA fibres by electrospinning method. Fibrous biocomposite mats consisting of PLA and CNCs have been electrospun from solvent or solvent mixtures such as l,l,l,3,3,3-hexafluoro-2-propanol (HFP), DMF/chloro-form and DMF/tetrahydrofuran (THF). The electrospun PLA/CNCs bionanocomposites have demonstrated rapid in vitro biodegradability and cytocompatible properties, and could be potentially suitable in tissue engineering.  

Nanocelluloses have been used as a nucleating agent to accelerate the erystallization rate of PLA. PLA/nanocellulose biocomposites frequently exhibit signifieantly improved thermal and mechanical and various other properties eompared to those of pure PLA. The tensile modulus and strength of neat PLA are generally improved with an increase of nanocellulose content. Inereased storage modulus at temperatures above Tg is often observed with the ineorporation of nanoeellulose in PLA, as well as decreased gas permeability. 

Kose and Kondo studied tbe size effects of cellulose nanofibres on the crystallization behaviour of PLA. They discovered that the smaller size of cellulose nanofibres on tbe nanoscale does not necessarily make a better nucleating agent for PLA. Table 9.1 summarizes the Avrami kinetic parameters for the isothermal crystallization of the PLA and PLA biocomposites with different types of nanocelluloses as compared to PLA composites with talc and nanoclay. With the addition of unmodified and silylated CNCs as nucleating agents, the t 2 value increases with increasing T similar to that of nanoclay and com starch, but opposite to that of talc. Comparing the 

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While techniques for preparation of nanocellulose-reinforced nanocomposite are different in complexity, they typically involve physically mixing and dispersing the nanocellulose and resin in a solvent system. In many cases, solvent exchange techniques are used, often along with surface modification of nanocellulose to make it compatible with organic solvents and/or the resin system. In this context, nanocomposite films from nanocellulose generally are prepared through three various techniques as below ... 

The mechanical properties of PLA/nanocellulose biocomposites are also strongly affected by the processing strategy and surface chemical modification of nanocellulose. Table 9.2 provides an overview of modulus, tensile... 

A summary of the different chemical modification techniques used to alter the surface characteristics of nanocellulose can be found in reference [47]. 

Figure 9.2 Surface modification chemistries of nanocellulose for PLA/nanocellulose biocomposites, a, Acetylation b, Esterification with various organic acids c, d, e, Grafting of PCL, PLA, P(CL-fi-LA) f, Silanization g, Silylation h, Carbojymethylation combined with hexanoation i, PEG grafting j, Modified with polyhedral oligomeric silsesquioxane (POSS).

Chemical modification on nanocelluloses stru les with one major challenge—to run reaction of modification so that it changes only the surface of nanosubstrate, while the original morphology... 

Dufresne et al. [153] noted that surface adsorption of potyojq ethylene chains on the surface nanocrystals can improve dispersibility and thermal stability of nanocrystals during the melt processing of polyethylene based nanocomposites. The chemical modification of cellulose is a most effective approach to avoid irreversible agglomeration during drying, and enhance the adhesion between nanocellulose and nonpolar matrices [132]. Dufresne et al. [98] showed also, that chemical and physical compatibilization imparted by poly(ethylene glycol) and polyoxyethylene layers promoted the interfacial interaction between cellulosic nanoparticles and polystyrene. 

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