Unmodified composites

Properties of Unmodified Composite Ceramic Sheets Used for Preparation of Electro-Catalytic Membranes... 

Gopalan Nair et ehemieally modified the chitin whiskers by using different coupling agents, namely phenyl isocyanate (PI), alkenyl succinic anhydride (ASA) and 3-isopropenyl-R, R -dimethylbenzyl isocyanate (TMI). These various chemieal treatments on chitin whiskers improve the adhesion between the chemically modified ehitin whiskers and the NR matrix. However, the mechanical performances of these NR composites markedly decrease after chemical modification. This is due to the partial or total destruction of the three-dimensional network of ehitin whiskers, which is assumed for the unmodified composites. 

Dufresne et al. studied stress vs strain curves (nominal data) for the chitin whiskers/unvulcanized NR evaporated composites, shown in Figure 14.12."" The polymeric matrix is in the rubbery state and its elasticity from entropic origin is ascribed to the presence of numerous entanglements due to high molecular weight chains. They further observed that the incorporation of anhydride and isocyanate modified chitin whiskers into NR lead to composite materials with improved mechanical properties. The study of the morphology of these nanocomposites leads to the conclusion that the various chemical treatments improve the adhesion between the filler and the matrix (Figure 14.13). However in some cases there is loss of performance, which could be due to the partial or total destruction of the three-dimensional network of chitin whiskers assumed to be present in the unmodified composites. 

Also isocyanates were used as adhesion modifiers. These compounds are efficient compatibilizers ensuring a significant improvement of tensile strength [50,51, 72, 83-86]. Qiu et al. [37] showed that the application of hexamethylenedi-isocya-nate causes increase of tensile strength by about 45% and bending strength by 85%, as compared to unmodified composites. Raj et al. [50, 72] noticed that application... 

Unmodified Composites Prepared by Simple Melt Mixing... 

The mechanical properties of the composite sheets made in laboratory are tested according to ASTM methods. The impact strength, however, was measured at -20 C using Charpy impact tester. All these test results simulate the properties of end product. Besides physical and mechanical properties the chemical characteristics of modified and unmodified composites can be very well correlated from Infrared spectroscopy and ESCA analyses data. 

In general, for a unmodified composite the viscosity decreases with increase in the polymer concentration. During reactive processing of composites the viscosity behavior of composite changes with fee addition of a reactive component even in trace quantity. Thus, fee addition of MAH-PP... 

In contrast to unmodified composites, the BMI modified composite showed a dramatic change in the mechanical strength with changing processing temperature. This is evident from Figure 4. The strength can be improved by about 30 to 40% over unmodified composite if BMI is introduced in the composite even at a low processing temperamre, i.e.. 

In the same study, CNs modified with carboxylation were also used, and although this had little effect on transport properties, better dispersion of filler in the polymer matrix was obtained. Interestingly, degradation for modified cellulose composites began at much higher temperatures than the unmodified composites, which the authors attributed to greater cross-linking in the modified composite. Transport... 

The strength of dispersion interaction of a solid with a gas molecule is determined not only by the chemical composition of the surface of the solid, but also by the surface density of the force centres. If therefore this surface density can be sufficiently reduced by the pre-adsorption of a suitable substance, the isotherm may be converted from Type II to Type III. An example is rutile, modified by the pre-adsorption of a monolayer of ethanol the isotherm of pentane, which is of Type II on the unmodified rutile (Fig. 5.3, curve A), changes to Type III on the treated sample (cf. Fig. 5.3 curve B). Similar results were found with hexane-l-ol as pre-adsorbate. Another example is the pre-adsorption of amyl alcohol on a quartz powder... 

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

It has been found that, for a fixed mineral filler content, the viscosity of PMF-based composites increases when the coat is made of polyethylene [164, 209, 293], poly(vinyl chloride) [316] and polypropylene [326, 327], The picture was different, however, for composites based on the ethylene/vinyl acetate copolymer to which kaolin with grafted poly (vinyl acetate) was added [336]. Addition of PMF with a minimum quantity of grafted polymer results in a sharp drop of flowability (rise of viscosity), in comparison to addition of unmodified filler but with a further increase of the quantity of grafted polymer the flow gradually increases and, depending on the kaolin content and quantity of grafted polymer, may even become higher than in specimens with unmodified filler, for equal concentrations. 

The authors of [344] investigated PS based composites prepared by compounding unmodified Aerosil with Aerosil to which a PS layer was grafted. The MM of the matrix and the grafted layer was 3 x 105. The resultant composites are characterized in Table 16 below. 

At low shear stresses the viscosity of PS based compositions with PMF is higher than that of compositions with unmodified filler the higher the shear stresses the closer the respective viscosities. 

Ultimate composition,.71 Ultraviolet spectrography compared with x-ray spectrography, 237-239 Unmodified scattering, 18, 20, 21 Uranium, determination, by x-ray emission spectrography, 187, 199, 203, 209, 234, 329... 

The results of the mechanical properties can be explained on the basis of morphology. The scanning electron micrographs (SEM) of fractured samples of biocomposites at 40 phr loading are shown in figure. 3. It can be seen that all the bionanofillers are well dispersed into polymer matrix without much agglomeration. This is due to the better compatibility between the modified polysaccharides nanoparticles and the NR matrix (Fig. 4A and B). While in case of unmodified polysaccharides nanoparticles the reduction in size compensates for the hydrophilic nature (Fig. 3C and D). In case of CB composites (Fig. 3E) relatively coarse, two-phase morphology is seen. 

The overall sorption value tends to decrease with the addition of the nanoclays. The decrease is maximum for the unmodified-clay-fiUed sample. As the ternperamre of swelling increases, the penetrant uptake increases in all the systems (Table 2.5). The rate of increase of solvent uptake is slower for the unmodified-clay-filled sample compared to the modified one. From Table 2.5 it can be seen that the values are higher for THE compared to MEK in every composite system. The higher sorption can be explained from the difference in solubility parameter of solvent and rubber (9 — 99 and polarity. The solubility parameter value of MEK, THE, and the mbber is 19.8, 18.6, and 14.8 MPa, respectively. This difference is lower (3.8 MPa ) in the case of THE than that of MEK (5.0 MPa ). 

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