Water Absorption Characteristics

Generally, incorporation of plant fibers into polymeric matrix increases the thermal stability of the system. In the thermal analysis of OPF-sisal fiber-NR hybrid composites also, it was foimd that addition of more fibers resulted in increase of thermal stability as indicated by the higher peak temperatures [35]. Increased thermal stability was also confirmed by the decrease in the activation energy of the composites. The thermal stability of NR-sisal fiber-OPF hybrid composites improved upon chemical modification [35]. However chemical modification resulted in lower activation energy (for decomposition) values compared to the untreated fiber composite. 

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Fleming et al. (18), using the procedure of Janicki and Walczak, also compared the water absorption characteristics of sunflower and soybean products. Water absorption of the soy products increased as protein content of the samples increased. Consistent with the findings of Lin et al. (17), water absorption of the sunflower products was below that of the soy products except for the concentrates, which had values similar to those of the soy counterpart, and the water absorptions of the sunflower concentrates and isolates were of similar magnitude. 

In recent years, there have been further improvements in the performance of zinc chloride cells. These have been brought about principally by use of laser welding to increase the internal active volume, and by improvements to materials, especially by synthesizing acetylene black with optimized surface area and water absorption characteristics. 

Acrylic. Acrylic resins (polymethyl methacrylate) have exceptional optical clarity and good weather resistance, strength, electrical properties, and chemical resistance. They have low water absorption characteristics. However, acrylics are attacked by strong solvents, gasoline, acetone, and similar organic fluids. 

INTEX SOFTENER 395 is a blend of softeners which produces a slick, soft hand on terry without sacrificing the water absorption characteristics. Application should be made by the typical wet-on-wet methods, or it may be applied in a conventional padding operation. 

The structure has primary and secondary alcohol groups uniformly interspersed throughout the length of the polymer chain. These hydroxy units impart high water absorption characteristics to the fiber and can act as reactive sites. The cotton fibers are hydrophilic and swell in water. It is hydrolyzed by hot acid and swollen by concentrated alkali. The cotton is treated with caustic soda solution (12 to 25 percent) under tension to develop a silk-luster and stop longitudinal shrinkage. This process is called mercerization. Mercerized cotton exhibits increased moisture and dye absorption. 

Equivalent or superior conductivity compared to other commercially available membranes Equivalent water absorption characteristics to Nahon-based membranes... 

Superabsorbent polymers are used as a liquid-absorber in food packaging systems. In these systems, the superabsorbent polymers absorb juice or water from fresh foods such as raw chicken, shellfish, and other meats or from frozen foods as they thaw. Chilled superabsorbent polymer gels may also be used as a dry-cooling medium. The water-swollen gel, contained in a durable plastic bag, is frozen and used to keep perishable foods cold. In addition to its liquid-water-absorption characteristic, superabsorbent polymers absorb water from the vapor state and therefore may be used to control humidity. 

The actual composition of the various acrylate grouts is considered proprietary data by the manufacturers (patent applications must, of course, reveal that information). It is believed that all of the grouts are mixtures of acrylate salts, selected for an optimum combination of low cost and solubility and water absorption characteristics. All require a cross-linking agent. For AC-400 this is shown in the manufacturer s literature to be methylenebisacrylamide, and is the source of the small toxicity hazard associated with the acrylates. All acrylate grouts use the same redox catalyst... 

Because of the improved thermal stability for PADS containing polyimides vis a vis other available siloxane polyimides, a screening program to correlate properties such as Tg, solubility, thermal stability, adhesion properties, and water absorption characteristics to structure was undertaken. Several copolymers were prepared from diamines and co-dianhydrides. An ODAN/ ODA copolymer in which 30 mole % PADS was substituted for ODAN, was prepared and TGA analysis at 450°C indicated that the material was the first siloxane containing polyimide identified that exceeded the established thermal stability criteria for interlevel dielectric applications. Stability and solubility of these materials as a function of PADS concentration is illustrated in Table VI. 

Sano, M., Negishi, M., Yamamoto, S., Baba, K., Kobayashi, S., 2005. Comparison of the water absorption characteristics of denture bases produced with sulfone and resin. J. Nippon Acad. Dental Tech. 26 10-15. 

Polymers containing hydrolysable groups or which have hydrolysable groups introduced by oxidation are susceptible to water attack. Hydrolyzable groups such as esters, amides, nitriles, acetals, and certain ketones can react with water and cause deterioration of the polymer. The dielectric constant, power factor, insulation resistance, and water absorption are most affected by hydrolysis. For polyesters, polyamides, cellulose, and cellulose either and esters, the hydrolysable groups are weak links in the chain, and hydrolysis of such polymers can cause serious loss of strength. A summary of water absorption characteristics of common plastic and rubbers is presented in Table 1.15. 

TABLE 1.15 Water Absorption Characteristics of Plastics and Rubbers... 

A. Akashi, Y. Matsuya, M. Unemori, A. Akamine, The relationship between water absorption characteristics and the mechanical strength of resin-modified glass-ionomer cements in long-term water storage. Biomaterials 20 (1999) 1573-1578. 

Effect of fiber treatments Alkali treatment of fibers slightly increased the density of composites as a result of low void content indicating better interfacial adhesion between matrix and fiber [39]. AlkaH treatment considerably reduced the porosity, indicating better fiber-matrix adhesion. The principal cause of increase in porosity in composites is the presence of voids in the fiber-matrix interface due to lack of compatibility. Study on water absorption characteristics of OPF-LLDPE composites [53] indicated alkali treatment on fibers reduced water absorption at higher fiber loadings of 40 and 50 percent. Composites made from alkaH-treated fibers exhibited more swelling compared to untreated fiber composites except at 50% fiber loading. Alkali treatment caused more linear expansion. 

Water absorption results of neat UPE and its composites reinforced with raw, mercerized and benzoylated fibers have been shown in Table 13.1. It can be seen from the table that water absorption characteristics of polymer composites depend upon the content of fiber loadings, water immersion time and surface modification techniques. The water absorption of raw and surface-modified fiber-reinforced UPE composites has been found to increase with the increase in percent loading. Similar results were also reported by Rashdi et ah during their studies on the water absorption behavior of kenaf fibers-reinforced polyester composites [27]. This may be due to greater affinity of water for OH groups present on the fiber backbone, whose number increases with the increase in fiber contents. In comparison to raw filler, composites reinforced with surface-modified filler exhibited low water absorption, which may be due to the reduction in the hydrophilic character of cellulosic biofibers after surface modification. 

Deb S, Braden M, Bonfield W (1995) Water absorption characteristics of modified hydroxyapatite bone cements. Biomaterials 16(14) 1095-1100... 

Silicone Hydrogels. A new class of hydrogels based on silicone has been developed (14). These materials were developed in an attempt to combine the high oxygen permeability of polydimethylsiloxane and the excellent water absorption characteristics of conventional non-silicone hydrogels. This new class of hydrogels was developed primarily for contact lens application. These silicone hydrogels are also prepared by free-radical poljnnerization techniques. 

The presence of the NH and CO groups in the molecule is the cause of the nylons absorbing water. The water absorption characteristics are given in Table 1.1. 

Many other properties have to be considered, especially for apparel fibres, e.g. moisture absorption, dyeability, drape, texture, weaving characteristics, etc. Many of the properties are strongly influenced by cross-sectional shape cotton is a round hollow fibre, whereas silk has a triangular shape giving it a fine lustre and rustle. Wool has a scaly surface and appears to be made up of two components which have different water absorption characteristics. This gives wool its crimpability and bulk. From studies like these, synthetic fibres can minimic natural fibres and can, in some cases, be more versatile. For example ... 

Sreekumar P. A., Selvin P. Thomas, Jean marc Saiter, Kuruvilla Joseph, Unni Krishnan G., and Sabu Thomas. (2009). Effect of fiber surface modification on the mechanical and water absorption characteristics of sisal/polyester composites fabricated by resin transfer molding. Composites Part A Applied Science and Manufacturing 4Q n), 1777-1784. 

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