Cellulosic nanocomposites with unique morphology and properties.

摘要

A new and environmental benign method for preparing regenerated cellulose and montmorillonite (MMT) biodegradable nanocomposites is developed using 4-methyl morpholine N-oxide (NMMO) as the solvent. Results showed that the modulus of the nanocomposites increases linearly at the MMT loading range of 1--10%. Using Wide Angle X-ray Diffraction (WXRD) analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation, it was found for the first time that the MMT was intercalated and exfoliated in the pure cellulose matrix.;Cellulose nanowhiskers reinforced poly(vinyl alcohol) (PVA) nanofiber web was successfully fabricated using electrospinning technique. The morphology and mechanical properties of highly aligned electrospun fiber webs were investigated. The relative alignment degree of electrospun fiber webs was analyzed using a fast Fourier transform (FFT) method. It was found that the modulus and tensile strength of aligned webs are higher than those of isotropic electrospun fiber webs. The relations of reinforcement effects, fiber alignment and cellulose nanowhiskers alignment have been investigated.;The mechanical properties of cellulose nanowhiskers reinforced poly(vinyl alcohol) (PVA) electrospun fiber rather than fiber webs have been measured using nanoindentation method. The modulus of PVA/cellulose nanowhiskers electrospun fiber increases linearly with increasing loading ratio of cellulose nanowhiskers up to 20.0wt%. Experimental results were compared with a longitudinal Halpin-Tsai model. The nanoindentation results are 20∼30% smaller than the longitudinal model predictions.;Ice-templated (IT) cellulose microfibril porous foams are successfully fabricated via unidirectional freezing methods. IT cellulose microfibrils foam prepared from 1.0wt% suspension shows a cross-linked network structure. As increasing the concentrations of cellulose microfibrils suspension from 1.0wt% up to 2.75wt%, a transition from a network structure to a lamellar channel structure happens gradually. As increasing the concentration of suspensions from 3.0wt% up to 8.0wt%, highly aligned channel structures parallel to the freezing direction were obtained. It was found that cellulose microfibrils are partially aligned along the freezing direction. It was found that the compressive stresses of IT cellulose microfibril foams increase linearly as increasing concentrations of suspension.;The morphology and growth mechanism of IT surfaces were investigated successfully using cellulose microfibrils and hydrophilic substrates. When the height of IT cellulose microfibril surface is 50 mum, the surface shows honey-comb like structures. When the height of IT surfaces is between 100 mum and 200 mum, a transition from honey-comb like structures to multilayer structures happens. In these cases, ellipse-shape channels are observed. If the height of IT surfaces is larger than 300 mum, fully developed multichannel surfaces are obtained. By controlling the temperature gradient between cellulose microfibril suspensions and secondary freezing mediums, various surface structures including honey-comb like structures, ellipse-shape channel structures, fully developed multichannel structures are obtained successfully. For the honey-comb like patterned surface, high contact angles are observed. On the other hand, for the layered patterned surface, anisotropic wetting properties were observed.