Sulfur fiber composites

Sulfur-fiber composites have been prepared and studied by a number of workers. Rods have been prepared (8) by passing parallel orientated glass strands through molten sulfur under vacuum to form rein-foroed bars 150 mm long and 6 mm in diameter. Glass-fiber mats have been impregnated with sulfur also, the mat being covered with powdered elemental sulfur and then placed in an oven at 185 °C for 1.5 hr so that polymeric sulfur is formed. 

The effectiveness of using the thermal input for EB crosslinking of carbon-fiber composite matrix materials to reduce dose was shown by M. Lavalle. Proper combinations of monomer, sulfur and metals subjected to ionizing radiation were found to produce nano-particles that could be of use in electronic applications. 

Sousa et al. [46] studied the mechanical properties of polypropylene (PP) composites reinforced with pretreated pineapple fibers with sulfuric solution. Pineapple fibers were extracted from residue SuFresh and dried at 80°C for 24 h. After being ground in a mill and sieved, the fibers were pretreated in a 350 L stainless steel reactor, under these conditions 1.0% (w/v) H SO solution in a 1 10 solid liquid ratio, 120°C for 10 min. 

Martin-Gullon, L, R. Andrews, M. Jagtoyen, and F. Derbyshire. 2001. PAN-based activated carbon fiber composites for sulfur dioxide conversion Influence of fiber activation method. Fuel 80(7) 969-977. 

For glass fiber composites, static fatigue limits correspond to about 60% of their instantaneous static, strength (Thomas 1960 Metcalfe and Schmitz 1972 Roberts 1978 Aveston et al. 1980 Chateauminois et al. 1993). However, significantly larger reductions in both crack initiation times and failure times were noted in several glass/polymer systems immersed in a solution of sulfuric acid (van den... 

Miscellaneous. In ore flotation, sodium sulfite functions as a selective depressant. In textile processing, sodium sulfite is used as a bleach for wood (qv) and polyamide fibers and as an antichlor after the use of chlorine bleach. Synthetic appHcations of sodium sulfite include production of sodium thiosulfite by addition of sulfur and the introduction of sulfonate groups into dyestuffs and other organic products. Sodium sulfite is useful as a scavenger for formaldehyde in aminoplast—wood compositions, and as a buffer in chrome tanning of leather. 

A variety of materials has been proposed to modify the properties of asphaltic binders to enhance the properties of the mix (112), including fillers and fibers to reinforce the asphalt—aggregate mixture (114), sulfur to strengthen or harden the binder (115,116), polymers (98,117—121), mbber (122), epoxy—resin composites (123), antistripping agents (124), metal complexes (125,126), and lime (127,128). AH of these additives serve to improve the properties of the binder and, ultimately, the properties of the asphalt—aggregate mix. 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

Some dicyanate-containing compositions, which contain rubbers as flexibilizing components, were described in the preceding chapters. There were also patent applications made, where dicyanates were claimed as additives in typical rubber mixtures. In such mixtures, butadiene-acrylonitrile rubber is used. The main components of such binders are nitrile rubber, BPA/DC and methylethylketone. They contain, moreover, Zn octoate and Fe203 [144] or ZnO and sulfur [145]. Isoprene-acryloni-trile rubber, BPA/DC prepolymer, Zn octoate, DABCO and benzoyl peroxide were dissolved in a methylethylketone-dimethylformamide mixture. Glass fiber was impregnated with the obtained solution [146]. 

Figure 25. Translation of fiber strength and interlaminar shear stress (ILSS) of the carbon/carbon composites of Figure 24 after four impregnation and carbonization (1000°C) cycles with coal-tar pitch and 12.5% sulfur (34).

Figure 26. Cross-sectional shrinkage as a function of heating rate during carbonization of unidirectional composites fabricated with high-modulus PAN-based fibers and pitch matrix under three conditions of pressure and sulfur content (20).

Figure 27. Flexural strength and bulk density of unidirectional composites subjected to graphitizing heat treatments either for each densification cycle or after the densification cycles were completed (20,52) The matrix was a coal-tar binder pitch with 10 wt.-% sulfur the high-modulus PAN-based fiber was Sigrafil HM.

---