摘要:

The conventional two-stage H2O2method was applied for bleaching rice straw and bagasse pulps. The pulps were bleached also by a nonconventional method: i.e., using different organic solvents with various contents in the first stage of the bleaching process. The effects of the kind and percentage of the organic solvent in the bleaching mixture on the properties of both the bleached pulps and paper sheets were studied and are discussed on the basis of the physicochemical properties of the bleaching mixtures.

ISSN:0360-2559    

DOI:10.1080/03602559608004054

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Temperature effects on thermodestructive processes in polymers are considered. The logarithm of lifetime of a linear polymer thin film on 1/T(inverse temperature) was found to be a smooth increasing curve tending to a limit at definite values of 1/T, characteristic of each polymer. Temperatures above which avalanche-like decomposition of polymers occurred were called “limiting.” To explain the dependence i t was assumed that associated and nonassociated monomer links are destroyed with different rate constants, the sequence of chemical acts in the process being the same. The rate constant of destruction of nonassociated monomer links is higher than that of associated links. Equilibrium of concentrations of associated and nonassociated monomer links is established much more quickly than the chemical reactions run. At rather low temperatures the reaction presumably runs at chain ends. As the temperature increases, the number (concentration) and the length of blocks consisting of nonassociated monomer links increase, also. When the length of such a block reaches a definite value, a break reaction occurs, the break constant increasing with the increase of the block length. The dependence of the process rate on temperature is determined both by concentrations of blocks of various length and by the temperature dependence of break rate constants. At a definite temperature the reactions presumably at the chain ends are substituted by chance reactions. At temperatures when intermolecular interactions can be neglected, thermodynamically unstable “polymer” gas appears which decomposes in an avalanche-like manner.

ISSN:0360-2559    

DOI:10.1080/03602559608004055

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

As a number code to the protein sequence language, the amino acid numbers (z) derived previously (1, 25, 45, and 17 prime numbers smaller than 64) are used to characterize oligopeptide motifs. The grammatical rule of this language is expressed with two theorems governing the collective properties of oligopeptides. This numeric representation contrasts particular sequence patterns. The language's equivalent forms range from simple repeating phrases (like in baby talk) to elegant and sophisticated seven-word poems (like those of Li Bai). Sequence examples are given for frequently occurring repeats in silk fibroin, collagen triplet repeats and mutational hotspots, ancient ferredoxin, coiled coil and leucine zipper patterns, runs of amino acids, protein “huntingtin,” hydrophobic transmembrane helices, implicit heptad repeats in amyloid protein, etc. A heptad scan method is applied to prion proteins that form amyloid through hydrogen bond zippers.

ISSN:0360-2559    

DOI:10.1080/03602559608004056

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effects of three types of high-density polyethylene (HDPE) resins (A, B, and C) and three antioxidants (vitamin E, Irganox 1010, and BHT) on the release of off-flavor (including off-odor and off-taste) from blow-molded HDPE bottles were investigated using sensory analysis and gas chromatography/mass spectrometry (GC/MS) analysis. Overall the sensory study showed that off- flavor intensity was affected by both resin type and antioxidant. Resin A bottles yielded less off-flavor compared to resin B or C bottles. Vitamin E containing bottles yielded less off-flavor compared to Irganox 1010 or BHT containing bottles for resins A and B; however, the antioxidants have almost the same effect on resin C. The GC/MS study identified more than 60 volatile compounds released from the bottles, ranging from C5to C20, which belonged to the groups ofn-alkane, 1-alkene, aldehyde, ketone, phenolic, olefin, and paraffin—among them aldehydes and ketones were the most important due to their very low odor thresholds. Resin A bottles yielded less aldehyde and ketone compared to resin B or C bottles. Vitamin E containing bottles yielded less aldehydes and ketones compared to bottles containing Irganox 1010 or BHT. There was a general consistency between the sensory and GC/MS data. The aldehyde and ketone concentration was linearly correlated reasonably well to odor (R2= 0.78) and taste scores (R2= 0.67). Another study was also conducted, which shows vitamin E has smaller reduction in melt flow index due to blow molding compared to Irganox 1010 or BHT.

ISSN:0360-2559    

DOI:10.1080/03602559608004057

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The study attempted to establish the optimum reaction conditions for obtaining soluble chloromethylated polystyrene with a transformation degree higher than 50%. A paraformaldehyde and chlorotrimethylsilane mixture as chloromethylation agent and SnCl4as catalyst were used. The transformation degree followed by the chlorine content depends on the following parameters: temperature, time, and [SnCl4]/[PS] and [Me3ClSi]/[PS] molar ratios.

ISSN:0360-2559    

DOI:10.1080/03602559608004058

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Two urethane diacrylates—one aromatic, M1100; and the other aliphatic, M1200—have been used to prepare elastic films under electron beam (EB) irradiation. Two monofunctional diluents are used;N-vinyl pyrrolidone (NVP) is used as the reactive diluent monomer, and the second one, called the codiluent, is chosen from a series of acrylated monomers withTgvalues lower than that of NVP. Pencil hardness; gel content; swelling ratio in acetone; and mechanical properties such as yield strength, break strength, elongation, and Young's modulus of the cured films are determined. Among the various codiluents used, vinyl acetate (VAc), cyclohexyl acrylate (CHA), and tertiary butyl acrylate (t-BA) played a significant role in inducing improved Theological properties in the cured films.

ISSN:0360-2559    

DOI:10.1080/03602559608004059

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Studies have been carried out on polyurethane elastomers based on modified castor oil in combination with different molecular weights of polyethylene glycol and polymeric methylene diphenyl-4,4′-diisocyanate (PMDI). The resulting polymers were cast into molds and the moldings were characterized by scanning electron microscopy and thermogravimetric analysis. Mechanical properties such as tensile strength, elongation at break, hardness, abrasion resistance, and compression set were measured. There is an increase in the flexibility of polyurethanes with increase in molecular weight of PEGs added to modified castor oil.

ISSN:0360-2559    

DOI:10.1080/03602559608004060

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0360-2559    

DOI:10.1080/03602559608004053

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor