Wiley

Một kỹ thuật được phát triển để thu được các phương trình tốc độ và các thông số động học mô tả sự phân hủy nhiệt của nhựa từ dữ liệu TGA. Phương pháp này dựa trên việc so sánh giữa các thí nghiệm được thực hiện ở các tốc độ gia nhiệt tuyến tính khác nhau. Bằng cách này, có thể xác định năng lượng kích hoạt của một số quá trình mà không cần biết dạng phương trình động học. Kỹ thuật này đã được áp dụng cho nhựa phenolic gia cố fiberglass CTL 91-LD, trong đó phương trình tốc độ - (1/w_e)(dw/dt) = 10¹⁸ e^−55,000/RT [(w ‐ w_f)/w₀,]⁵, nr.⁻¹, đã được tìm thấy áp dụng cho phần lớn của sự phân hủy. Phương trình đã được thử nghiệm thành công bằng nhiều kỹ thuật khác nhau, bao gồm so sánh với dữ liệu nhiệt độ không đổi có sẵn trong tài liệu. Năng lượng kích hoạt được cho là chính xác trong khoảng 10 kcal.

The α‐dispersion in many polymer systems is the process to be associated with the glass transition temperature where many physical properties undergo drastic changes. We have measured and analyzed the complex dielectric behavior of the α‐dispersions for five polymers [i.e., polycarbonate and polyisophthalate esters of bisphenol A, isotactic poly‐(methyl methacrylate), poly(methyl acrylate), and a copolymer of phenyl methacrylate and acrylonitrile] and have found that the usual methods of analysis cannot be used to represent the data. However, it is possible to represent the relaxation process as the sum of two dispersions but there is no evidence to support this contention. An empirical expression is proposed to represent the data. This expression which takes the form of appears to be a general representation for the three known dispersions, i.e., Debye, circular arc, and skewed semicircle. The complex dielectric constants calculated with the aid of this expression and the parameters for each polymer system which was determined graphically were found to be in excellent agreement with the experimental complex dielectric constants. This method of representation was extended to sixteen α‐dispersions reported in the literature always with excellent results.

We propose an equation, based on “reciprocal” mean and force additivity, for calculating the interfacial tension between polymers or between a polymer and an ordinary liquid: where γ₁₂ is the interfacial tension; γ_i the surface tension; γ and γ the dispersion and polar components of γ_i, respectively. This equation is shown to predict accurately the interfacial tension between polymers or between a polymer and an ordinary liquid. Fowkes' equation or Fowkes' equation with a geometric‐mean polar term 2(γ_iP_γ2p)^1/2 is not applicable to polarlpolar systems. The interfacial tension arises mainly from disparity in the polarities of the two phases. The above equation can also be used to calculate the surface tension and polarity of polymers or organic solids from contact angle data.

Cellulose strongly adsorbs cellulase at pH 4.0‐5.0, 25‐50°C, conditions which are optimum for the enzyme action. The adsorbed enzyme is sufficient to digest the cellulose with no replenishment of enzyme even though the liquid phase containing the sugar is continuously removed. As cellulose is digested, the released enzyme is readsorbed on excess or newly added cellulose with retention of activity. Sugars can be separated from the enzyme‐cellulose complex by simple filtration or centrifugation or by retaining the enzyme‐cellulose complex in a column from which the sugar solution is eluted. Adsorbed cellulase has been used to produce syrups containing 5‐14% glucose continuously from stirred reactors containing 10‐20% cellulose, or from cellulose columns.

Thermal analysis of a hardwood reflected the pyrolysis of its main components including xylan and cellulose. Thermal properties of these components were investigated with model compounds consisting of α‐D‐xylose, substituted phenyl β‐D‐xylopyranosides, β‐Dglucopyranosides and α‐D‐arabino‐hexopyranosides and 1,6‐anhydro‐β‐D‐glucopyranose.

At the lower temperatures these molecules displayed anomerization, loss of water and phase change, which were studied with a variety of physical methods. Calorimeteric and wide line NMR measurements showed that 1,6‐anhydro‐β‐D‐glucopyranose and related anhydro sugars undergo plastic crystalline transition, involving reorientation of the molecules about their centers of gravity and self‐diffusion before melting.

At more elevated temperatures the above compounds showed cleavage of the glycosidic group, polymerization of the sugar moiety, decomposition and evaporation of the pyrolysis products. This involved some heterolytic reactions, which could be catalyzed by acid or alkaline materials.

Kinetics of the pyrolysis process, including the rates and energies of activation were determined by thermal analysis and ESR spectroscopy. These data indicated that cleavage of the glycosidic bond is directly influenced by variation of its electron density and constitutes the rate determining step in pyrolysis of the carbohydrate compounds.

Information is presented to show that the total volume of micropores in acetic acid swollen fibers correlates closely with acetylation reactivity. Pore size distribution measurements indicate that the pores with diameters of 25–75 Å may be particularly influential for promoting reactivity since fibers which perform well in acetylation processing have a characteristically high volume of pores in this size range. Internal surface area also correlates with acetylation reactivity if allowances are made for the large fraction of surface area which is associated with pores that are too small for reagent penetration. This lower limit is calculated to be 20–25 Å. Based on estimates of void spaces within and between the cellulose structural building units, acetylation of acetic acid swollen fibers should occur on the external surfaces of the elementary fibrils, the microfibrils and the lamellae as well as on the internal surfaces of the microfibrils and the lamellae. The overall effect of cellulose structure on reactivity seems to be the control of the inward flow of reagents to reaction surfaces but not the outward transport of reaction products. Internal void volume may function to accommodate reaction products as they swell inwardly and thus provide a means for allowing the reaction to go to completion. The relationship between cellulose structure and reactivity can be extended to chemical reactions other than acetylation.

The grafting of acrylic acid (AAc) to starch was investigated with gamma‐pre‐irradiated starch and aqueous solutions of AAc. The rate of grafting increased initially with time, then decreased, and approached zero when the percentage grafting reached a maximum value. At a given radiation dose the rate of grafting was proportional to the first power of the concentration of irradiated starch and to the 1.5 power of the initial concentration of AAc. Solvent effects on degree of grafting, molecular weight, and number of grafted branches were evaluated. Higher degrees of grafting were achieved with electron‐irradiated starch at radiation doses lower than those used with gamma rays.

The theta temperatures for linear polyethylene in diphenyl, diphenyl methane, and diphenyl ether were determined by the precipitation temperature measurements. The unperturbed mean‐square end‐to‐end distance (R₀²) and its temperature variation d In (R₀²)/dT were estimated from direct intrinsic viscosity measurements in these three theta solvents: <R₀²/nl² (where n is the Dumber of bonds, and l is the bond length) in diphenyl, diphenyl methane, and diphenyl ether was 7.10 at 127.5°C, 6.99 at 142.2°C, and 6.80 at 163.9°C., respectively. These numerical values gave d In <R₀²/dT = −1.21 × 10⁻³ deg.⁻¹. The results obtained here were in good agreement with those reported by Flory^1,2 and Chiang,³ and in support of the theoretical calculation by Hoeve⁴ and Nagai⁵.

Commercial samples of cis‐1,4‐polybutadiene and trans‐1,4‐polybutadiene have been chlorinated with chlorine gas in a chloroform solution and precipitated with methanol. The precipitates were thoroughly washed with a large amount of methanol and dried in vacuum at 40°C. The samples were fractionated with the tetrahydrofuran‐water system at 40°C. The viscosity measurements were made at 30°C. in various solvents. The light‐scattering measurements were made with a modified Brice‐type light‐scattering photometer with unpolarized blue light and with a cylindrical cell, over the angular range from 35° to 145°, at room temperature. The relation between the intrinsic viscosity and the molecular weight was obtained for each sample. The unperturbed mean‐square end‐to‐end distance was estimated by the Stockmayer‐Fixman equation, and was used for calculating the conformational parameter \documentclass{article}\pagestyle{empty}\begin{document}$ \sigma = \;(\overline {r_0 ^2 } /\overline {r_{0f} ^2 })^{1/2} $\end{document} for each chlorinated sample. The relation between the chemical configuration and the chain conformation for each chlorinated sample was discussed in terms of the unperturbed molecular dimension and rotational isomers of model compounds for a rotation around the CC bonds in the main chain.