They have developed new methods for testing permeability and durability of the microbial barrier intended for testing multiple use medical cellulosic textiles, employed primarily as wrapping materials in sterilization.
The method for testing permeability of the microbial barrier in dry conditions can also be applied for testing permeability of microorganisms in uniforms of the medical staff. The efficiency and durability of the microbial barrier, conditioned by different process parameters, were determined. Maximum number of the washing and sterilization cycles was defined with respect to the loss of functionality or barrier properties. Bacterial spores of the Bacillus genus were used Geobacillus stearothermophilus and Bacillus atrophaeus as the only dry form of microorganisms whose primary purpose is biological control of sterilization.
This work is of special interest since microorganisms in dry form were used as opposed to the suspensions of different types of microorganisms used in similar research. Testing was conducted after 1, 10, 20, 30 and 50 washing and sterilization cycles under real hospital conditions. The composite materials prepared using both matrices and cellulose fibres treated with MPS and MRPS displayed good mechanical performances.
HDS-treated fibres enhanced the composite properties only modestly, which was attributed to the incapacity of HDS to bring about covalent bonding with the matrix. Composite materials based on cellulose aceto-butyrate as a matrix and cellulose fibres from softwood long fibres SLF and avicell powder as reinforcing elements were prepared .
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The main idea of such an approach is the use of stiff monomers able to react with the cellulose surface with only one of the functionalities, thus leaving the remaining second moiety to couple with the polymer matrix during composite processing. Such a system gives rise to the formation of a covalent linkage between the matrix and the reinforcing elements and enables perfect stress transfer between the matrix and the reinforcing elements.
The stiff character of the used molecules excludes the reaction of both functionalities at the surface of the same fibre whereas their quite small size avoids bridging two fibres. The modified fibres were submitted to solvent extraction prior characterization by elemental analysis, infrared and X-ray photoelectron spectroscopy, scanning electron microscopy SEM and contact angle measurements.
All these techniques confirmed the occurrence of the grafting. The modified fibres have kept their biodegradable character, as illustrated by Figure 3. The modified fibres were then incorporated into cellulose acetate-butyrate and natural rubber matrices. Pasquini et al. The occurrence of chemical modification was checked by X-ray photoelectron spectrometry.
The modified fibres were then used to reinforce low density polyethylene and showed that the surface chemical modification resulted in improved interfacial adhesion with the matrix and much more homogeneous distribution of the reinforcing elements into the matrix. Even though, the surface modification did not induce an improved mechanical performance of the ensuing composites.
This surprising finding was attributed to the fact that the modification procedure affected negatively the degree of polymerisation of the fibres and their intrinsic properties zero tensile strength. The degradation of these two parameters was associated to the hydrolytic action of acid chloride molecules released during the modification with alcanoyl acids chlorides.
Different Egyptian industrial crops, namely: cotton stalk, rice straw, bagasse, and banana plant waste were used as a starting raw material to produce lignocellulosic fibres, which were incorporated into organic matrices . The matrices used were low density polyethylene and stearic acid as compatibilizer, or maleated low density polyethylene. The properties of the prepared composites were studied by differential scanning calorimetry DSC , tensile tests and scanning electronic microscopy SEM. As expected, enhanced mechanical properties were obtained when using maleated LDPE as compatibilizer.
The chemical composition of fibres, in terms of lignin, cellulose and hemicelluloses contents, was found to have a strong influence on the mechanical properties of the composites. Long and short date palm tree fibres were combined with an epoxy matrix to produce composite materials .
This study permitted to establish that strong interactions between both components and etherification reactions may occur between the hydroxyl groups of the fibres and the epoxy groups of the epoxy-amine reactive mixture Figure 4. These effects were emphasized when decreasing the size of the fibres.
The higher adhesion between the short fibers and the polymeric matrix, as well as an increased glass transition temperature resulted in a lowered molecular mobility and water absorption level. Short date palm tree lignocellulosic fibres were incorporated into poly propylene and low density polyethylene matrices, in the presence of maleic anhydride copolymers, as compatibilising agent .
The reinforcing efficiency of the unmodified fibres was found to depend on the nature of the matrix, particularly on their degree of crystallinity. The compatibilization enhanced the mechanical performances for both sets of composites up to a critical amount.
Last year we had the opportunity to test the effect of the fibres modification in cement based composites . The surface modification was found to affect the fibre-matrix interface and the mineralization of the fibre lumen, as evidenced by scanning electron microscopy SEM with backscattered electron detector. The accelerated ageing cycles showed that MRPS-modified fibres were well protected, since they were free from cement hydration products. Instead, APS-modified homologues underwent rapid mineralization. These observations helped understanding the mechanisms of degradation of fibre-cement composites.
Our group has a long tradition in studying nanocomposites based on cellulose, starch or chitin nano-reinforcing elements. This field has attracted the attention, scrutiny and imagination of both scientist and industrial communities in recent years. Behind the push for nanocomposites, a large window of opportunity has opened to overcome the limitations of traditional micrometer-scale composites.
Research in this scope is literally exploding because of the intellectual appeal of building blocks on the nanometer scale and because the technical innovations permit to design and create new materials and structures with unprecedented flexibility, improvements in their physical properties and significant industrial impact. Stable aqueous suspensions of polysaccharide nanocrystals can be prepared by acid hydrolysis of the biomass .
The biomass is generally first submitted to a bleaching treatment with NaOH in order to purify the polysaccharide by removing other constituents. The bleached material is then disintegrated in water, and the resulting suspension is submitted to a hydrolysis treatment with acid.
The amorphous regions act as structural defects and are responsible of the transverse cleavage of the microfibrils into short monocrystals under acid hydrolysis. Under controlled conditions, this transformation consists of the disruption of amorphous regions while leaving the monocrystalline segments intact. It is ascribed to the faster hydrolysis kinetics of amorphous domains compared to crystalline ones. The resulting suspension is subsequently diluted with water and washed by successive centrifugations. Dialysis against distilled water is then performed to remove free acid in the dispersion.
Complete dispersion of the whiskers is obtained by a sonication step. The study of cellulosic nanoparticles as a reinforcing phase in nanocomposite films started fifteen years ago  and since this time, a huge amount of literature has been devoted to nanocellulose which is becoming a topical subject as revealed from the abundant literature. Nanocomposites films have been processed from nanoplatelet-like starch particles and plasticized and disrupted starch granules with water and sorbitol .
The nanocomposite films were processed by film-casting from a mixture of the aqueous suspension of starch nanocrystals with the gelatinized starch. The thermal and mechanical properties of the nanocomposite films were determined before and after accelerated ageing. Whiskers from tunicin, the cellulose extracted from tunicate, a sea animal, were used in combination with sorbitol plasticized waxy maize starch to produce nanocomposite materials .
The mechanical properties of the prepared materials were studied in the linear and nonlinear deformation domains. The prepared nanocomposites displayed good mechanical strength due to the strong interaction between tunicin whiskers, matrix, plasticizer sorbitol , and water. In addition, the capacity of the cellulose filler to form a stiff three-dimensional network thanks to hydrogen bonds, contributes to this enhancing power.
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High loading level induced a decrease in the crystallinity of the amylopectin phase. The mechanical strength increased linearly with filler contents, indicating that an effective stress transfer from the matrix to the whiskers took place. As expected, the mechanical properties of the nanocomposites strongly depended on the relative humidity conditions of the surrounding atmosphere.
Copolymers of polyvinyl alcohol and polyvinyl acetate and a colloidal aqueous suspension of cellulose whiskers prepared from cotton linter were mixed with the aim of preparing nanocomposite materials . The degree of hydrolysis of the matrix was varied in order: i to vary the hydrophilic-hydrophobic balance the polymer matrix; and ii to influence the degree of interaction between the filler and the matrix. The prepared nanocomposite films were conditioned at various moisture contents and their dynamic mechanical and thermal properties were established using dynamic mechanical analysis and differential scanning calorimetry, respectively.
Tensile tests were also performed at room temperature to estimate mechanical properties of the films in the non linear range. Conditioning the films in moist conditions revealed that there is a water accumulation at the reinforcing elements-matrix interface. The reinforcing effect was found to increase with increasing the degree of hydrolysis of the matrix. Nanocrystals from ramie fibres and waxy maize starch granules were grafted by polycaprolactone PCL chains with various molecular weights, using isocyanate-mediated reaction .
The modified nanoparticles were characterized by X-ray diffraction analysis and contact angle measurements, which showed that the nanoparticles kept their initial morphological integrity and native crystallinity. The grafting of PCL chains induced a decrease in the modulus values and an increase in the strain at break. Chitin whiskers were isolated and polycaprolactone grafted CHW-g-PCL in view of preparing thermoformable bionanocomposites . The grafting was achieved by initiating the ring-opening polymerization "grafting from" strategy of caprolactone monomer onto the CHW surface under microwave radiation.http://ipdwew0030atl2.public.registeredsite.com/373673-how-to.php
Cellulose-reinforced composites: from micro-to nanoscale
The bionanocomposites prepared were injection-moulded forming a co-continuous phase mediated with the entanglement of grafted PCL chains. It was established that increasing the PCL content in CHW-g-PCL films, induced an increase of the strength and elongation as well as of the hydrophobicity of the nanocomposites. New nanocomposites of waterborne polyurethane WPU as a matrix were prepared by filling low loading of starch nanocrystals StNs as a nano-phase . The chemical grafting of the StNs did not affect positively the strength and elongation, because such a treatment inhibited the formation of physical interaction and increasing network density in nanocomposites.
Journal of Polymer Engineering
Cellulose rodlike nanocrystals whiskers were surface-grafted with polycaprolactone PCL via microwave-assisted ring-opening polymerization yielding filaceous cellulose whisker-graft-polycaprolactone nanocrystals CW-g-PCL , which were incorporated into poly lactic acid PLA as a matrix . The thus prepared reinforcing elements showed superior enhancing power of the mechanical performance of PLA-based materials compared to platelet-like nanoparticles of starch-g-PCL. In fact, approximately 1.
An elegant way of valorising industrial crops was the preparation of cellulose cassava bagasse nanofibrils CBN reinforced cassava starch CS , both being industrial by-products . The resulting CBN displayed a relatively low degree of crystallinity. Their morphological characteristics were the following: a thickness of around nm and a length of nm. For impregnation of the fibers, is injected through the mould at low pressure. There is an another variety of this process known as the vacuum injection or vacuum-assisted resin transfer molding VARTM , where a foil or polymeric film is used with a single solid mould.
For the development of the process the influence of various parameters such as is of great importance.
The viscosity of the resins used should be low enough for proper wetting of the fibers. Several types of resins can be used for RTM such as epoxy, polyester, phenolic, acrylic etc.
Rapid fabrication of complex, high performance and large parts can be achieved through this method. It is a technique where a semi-finished composite sheet or sheet molding compound is compression moulded using a rolling resin film, and fibers are added on to it.
Related Cellulose and Cellulose Composites: Modification, Characterization and Applications
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