R. D. Gilbert

Lignin-based carbon fibers for composite fiber applications

Abstract Carbon fibers have been produced for the first time from a commercially available kraft lignin, without any chemical modification, by thermal spinning followed by carbonization. A fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum. Blending the lignin with poly(ethylene oxide) (PEO) further facilitated fiber spinning, but at PEO levels greater than 5%, the blends could not be stabilized without the individual fibers fusing together. Carbon fibers produced had an over-all yield of 45%. The tensile strength and modulus increased with decreasing fiber diameter, and are comparable to those of much smaller diameter carbon fibers produced from phenolated exploded lignins. In view of the mechanical properties, tensile 400–550 MPa and modulus 30–60 GPa, kraft lignin should be further investigated as a precursor for general grade carbon fibers.

Lignin-Based Carbon Fibers

Carbon fibers are one of the most important engineering materials in advanced composites. They are lightweight, fatigue resistant materials that possess high strength and high stiffness. These unique properties result from their flawless structure and the development of highly anisotropic graphic crystallites orientated along the fiber axis during the production process.1 Carbon fibers are manufactured by thermally treating fibers at 1000-2000 ℃ in an inert atmosphere while maintaining the fibrous structure. This is aided by a stabilization stage in which the precursor fibers are heated under tension at 200-300 ℃ in the presence of air. This causes crosslinking on the fiber surfaces, among other reactions, and prevents shrinking, melting and fusing.

Biodegradable Cellulose Block Copolymers

Abstract Biodegradable polymers can be prepared by the incorporation of cellulose oligomeric blocks into the polymer backbone. Block copolymers prepared by reacting equimolar amounts of depolymerized cellulose triacetate (CTA) with MDI or TDI and block terpolymers prepared by reacting the CTA oligomer with poly (propylene glycol) capped with MDI or TDI were deacetylated and incubated with cellulysin at pH 5 and 50 °C. The intrinsic viscosity of each copolymer decreased substantially even after 10 hr incubation time. There was negligible acid hydrolysis. Cellulose showed a smaller decrease at the same incubation time-probably due to its lower accessibility. Methods for incorporating cellulose oligomeric blocks and other biodegradable blocks into different types of polymers are discussed.

Fourier transform infra-red spectroscopy of nylon-6 blends: binary blends with poly(methyl methacrylate) and ethylene vinyl ester/alcohol copolymer

Abstract Films of blends of nylon-6 with poly(methyl methacrylate), (PMMA) and poly(ethylene-vinyl alcohol) were cast from formic acid solutions and examined by Fourier transform infra-red spectroscopy. At high contents of nylon-6 the vinyl alcohol of the copolymer reacts with formic acid to form vinyl formate. In contrast, the films of 100% copolymer and of the 25 75 and 10 90 blends contained both the alcohol and the ester groups. The FT i.r. results indicate that there are specific interactions between the amide group on nylon-6 and the ester group of PMMA or the copolymer. Data are also presented which show that there are at least two amorphous phases - one miscible containing both the polymers and the other containing almost pure noncrystallizable component. The differences in the specific interactions in the two blend systems are largely due to the inversion of the ester group in the pendant chain.

Electron spin resonance study of a cured epoxy resin exposed to high-energy radiation

Abstract Tetraglycidyl-4,4′-diaminodiphenyl methane cured with 4,4′-diaminodiphenyl sulphone was irradiated with varying dosages of 0.5 MeV electrons and 1.17 and 1.33 MeV gamma rays and was studied using electron spin resonance. The radical concentration increases with increasing radiation dose and decays, at ambient temperature, in a way consistent with a model that assumes two simultaneous second-order reactions occurring in different zones.

Inorganic Content of Cotton Dusts, Trash, and Bracts

The exact etiological agents responsible for the biological effects of cotton dust are unidentified, but most investigators believe they are organic in nature. Inorganic compounds have not been considered as significant factors. However, cotton dusts, trash, and bracts have high inorganic contents (7–43% ash), as reported here; more importantly, aqueous extracts of the trash and bracts have inorganic contents as high as 65%, which means a significant amount (10–36%) of the inorganic compounds in trash or bract is water extractable. Elements present in the ash include: N2, Cl2, P, K, Ca, Mg, Mn, Cu, Zn, S, and O2. KCl and K2SO4 have been definitively identified. It is suggested that greater attention should be given to the inorganic nature of cotton dust in the etiology of byssinosis.

Chemical Composition of Cotton Dusts Part II : Analyses of Samples Collected in a Model Card Room

The ash and protein contents of Pneumafil (PN) trash samples collected in a model card room and of the aqueous extracts of these samples arc reported here. The average ash content of these samples is 12.5% (σ = 4.2%). The average ash content of the dried aqueous extracts of these samples is much higher than that of the raw samples (mean 36.9%, σ = 10.8%). The average protein content of these samples and their dried aqueous extracts are about the same (13.2 and 14.9%, respectively). Trash samples from cotton grown under dry, arid conditions tend to have relatively high inorganic contents. Steaming tends to reduce the inorganic fraction of both the raw samples and their dried aqueous extracts but has little effect on the protein content. Increasing the number of gin lint cleaning stages reduces the dust level in the card room but has little effect on the proximate chemical composition of the PN samples. The fraction of ash in the PN dust tends to increase as the grade of cotton improves. Respirable dust collected from an electrostatic precipitator and respirable dust separated from lint trash are shown to have very high inorganic contents (41.3 and 37.1%, respectively). The average ash content of five samples rollected on the vertical elutriator was 20.1%, a value close to the average ash content of leaf and bract samples.

Chemical Composition of Cotton Dusts Part I: Analyses of Cotton Plant Parts, Gin Trash, and Weed Samples

Cotton plant parts are thought to be a major source of dust generated during cotton processing. Their chemical composition is important with regards to identifying the causal agents of byssinosis. Reported here are the ash and protein contents of cotton bract, leaf, stem, burr, and gin trash samples and of their dried aqueous extracts. The average ash contents of the above samples are 18.0, 16.6, 7.2, 7.5, and 19.1%, respectively. Significantly, the average inorganic contents of dried aqueous extracts are from two to five times higher than those of the raw samples.. The average protein contents of the above samples are 12.5, 17.4, 8.6, 5.7, and 13.6%, respectively. The average protein contents of the dried aqueous extracts of bract, leaf, and gin trash samples are about the same as the raw samples. The protein of the dried aqueous extracts of stem and burr increases markedly compared to the raw samples (from 8.6 to 21.3% and 5.7 to 15.5%, respectively). Ash and protein contents of several weed samples have been analyzed, and their extracts are approximately the same as stem and burr samples. The fraction of each sample that is extractable by water is about the same (ca. 13%) for all plant parts, gin trash samples, and weed samples investigated in this study.

Melt spinning of thermotropic cellulose derivatives

The melt spinning of two thermotropic cellulose derivatives—trimethyl silyl cellulose and phenyl acetoxy cellulose—is described in this article. Removal of the substituents was facile, rapid, and essentially complete. Both the melt-spun and regenerated fibers had banded textures typical of fibers spun from a liquid crystalline phase. The regenerated cellulose fibers had high strengths and moduli compared to viscose rayon and Lyocel cellulose fibers.

Arylazo dyes containing a built-in hindered-amine moiety

Abstract This paper describes the synthesis, spectral properties, and photolytic behavior of some 5-arylazo-6-hydroxy-y-carbolines. Like 1-arylazo-2-naphthols, these novel dyes exist primarily in the hydrazone form. Interestingly, however, the arylazo-γ-carboline dyes are significantly more light-stable in a polymer matrix than their 1-arylazo-2-naphthol counterparts. This suggests that the use of a built-in hindered-amine residue is an effective way to inhibit the lightinduced oxidation of arylhydrazone-type dyes. The preparation of novel nitroxide derivatives of the arylazo-γ-carbolines for electron spin resonance spin-probe studies is also described.