摘要:

AbstractThe application of differential thermal analysis (DTA) for the characterization and the investigation of the thermal degradation of synthetic textile fibers, to include polyester, nylon 6, propropylene, and polytetrafluoroethylene fibers, has been studied. The temperature range was from 50 to 650°C. using laboratory‐built DTA apparatus. Experimental considerations and techniques are discussed and such variables as sample preparation, size, cell packing, atmosphere control, and heating rate have been investigated. The conventional technique of grinding or milling DTA samples is shown to cause significant changes in certain samples, particularly in undrawn fibers. The control of sample atmosphere by dynamic gas flow through the sample cell gave peaks that were generally sharper and larger than those found when control was by gas diffusion. Data are given on the various low temperature transitions found in such fibers. Significant differences in low temperature transitions were observed between polypropylene fiber and the bulk polymer as well as between drawn and undrawn nylon 6 fibers. The interpretation of the DTA curves for the decomposition and other reactions at elevated temperatures is discussed. Nylon 6 and polypropylene showed only endothermic reactions indicative of depolymerization processes whereas other fibers showed both endothermic and exothermic reactions in the decomposition ran

ISSN:0449-2994    

DOI:10.1002/polc.5070060103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractDifferential thermal analysis (DTA) was used to measure crystallization, melting, and glass transition temperatures of poly(ethylene terephthalate), poly‐1,4‐cyclohexylene‐dimethylene terephthalate, and some copolyesters. These values are affected in different ways by systematic changes in such factors us copolymerination, molecular block formation, crystal perfection, nucleation, thermal history, and orientation. At least two types of abnormally high melting structures were formed and identified. The stability of these polymers to thermal and oxidative degradation was studied b

ISSN:0449-2994    

DOI:10.1002/polc.5070060104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractDifferential thermal analysis and thermogravimetric analysis were used to evaluate the thermal properties of several types of polyurethane elastomers. The composition of the polymers investigated was changed by varying the substrate, or soft segment, diisocyanate and extender. The data indicated that within the limits of the compositions under study, polyurethanes were thermally stable to their melting points, however, above the melt they were susceptible to oxidation unless stabilized by the addition of an antioxidant. On the differential thermograms the absence of a pronounced endothermic peak at the melting point, characteristic of non‐crystalline polymers, was observed. The decomposition of polymers made with 4,4′‐diphenylmethane diisocyanate (MDI) occurred above 400°C. and was at least a two‐step process, while the decomposition of polymers containing toluene diisocyanate (TDI) occurred below 400°C. and appeared to be a one‐st

ISSN:0449-2994    

DOI:10.1002/polc.5070060105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractThe specific heat and the specific volume of the different crystal modifications of poly‐1‐butene were investigated. Modification III, the crystalline structure of which is still unknown, was obtained by precipitating the benzene solution with methyl acetate. At 101°C. it is transformed into the tetragonal phase which melts at 121.5°C. The specific heat of the rhombohedrie structure, which was obtained from the melt by cooling and storage over a long period, increased evenly with a rise in temperature Up to its melting point; by immediately measuring a freshly cooled melt, the specific heat of the tetragonal modification (at least above 80°C.) was obtained. A predominantly atactic material which had been stored for a long period, indicated the melting at 87°C. of the small fraction of the rhombohedric crystals. The investigations were supplemented by dilatometric measurements. By means of the degree of crystallinity thus obtained, the heats of fusion were calculated and compared with values from measurements conducted on the melting point depression of m

ISSN:0449-2994    

DOI:10.1002/polc.5070060106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractThe three polymorphic forms of polybutone‐1 may be easily characterized by DTA: Form I has a DTA peak near 132°C; Form II has a peak near 118°C; and Form III has doublet peaks at 104° and 118°C. The kinetics of the room temperature transformation of Form II to Form I have been qualitatively investigated by DTA. The results indicate: (1) the thinner the film the faster the conversion rate and (2) the greater the catalysis residue in the system, the faster the conversion to Form I. The doublet in the Form III thermogram is due to the fact that the 104°C. transition corresponds to a phase change III to II with the 118°C. transition merely being the normal melting transition of Form II. Indeed, it is possible to heat Form III polybutene to 110°C, quench; and on standing it is found that the product has reverted t

ISSN:0449-2994    

DOI:10.1002/polc.5070060107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractThe melting and crystallization behavior of polyethylene samples has been investigated by differential thermal analysis (DTA), with special emphasis on the effects of thermal conditioning on the crystalline state of the sample. Techniques are outlined for impressing a wide variety of thermal histories on the sample in the DTA cell. In particular, the use of an annealing procedure is shown to provide a significant evaluation of the extrapolated value of the equilibrium melting temperature, combined with a rapidity not possible by the dilatometric method. Theoretical implications of the various procedures and results are briefly discussed. Critical examination of the fine structure observed in the melting thermograms leads to the conclusion that under certain conditions crystallites originating from both heterogeneous and homogeneous nucleation can be detected. The temperature rise associated with very fast crystallization is considered to influence the subsequent melting temperature more significantly than the effects of re‐crystallization during the actual melting cycle. Some illustrations are given of the general usefulness of the conditioning procedures in clarifying phenomena observed with various sample

ISSN:0449-2994    

DOI:10.1002/polc.5070060108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractIn the combustion of wood, the α‐cellulose fraction contributes most of the flaming; the lignin fraction supports the major part of the glowing. In the present study, thermogravimetric and differential thermal analyses were conducted to determine the affect of low concentrations of flame retardants on the kinetics of pyrolysis and phenomena of combustion of α‐cellulose. The flame retardants investigated—sodium tetraborate, aluminum chloride, potassium bicarbonate, and ammonium phosphate—were found to lower the active pyrolysis temperatures and increase the yield of chars. The kinetic data obtained by then no gravimetric analysis of the treated ‐cellulose in vacuum suggest that at least two mechanisms :ire involved. The early stage is controlled by pseudo‐zero‐order and the late stage is of pseudo‐first‐order. Sodium tetraborate and aluminum chloride caused little reduction in activation energies. Ammonium phosphate decreased the activation energy mostly in the early stage. Potassium bicarbonate lowered activation energies of both stages. Further thermal analysis in helium and oxygen showed that flaming combustion of α‐cellulose was substantially reduced by treatment, and its exothermic peak occurred near the end of pyrolytic volatilization. The heat of pyroiysis was reduced significantly by treatment. The heat of combustion is distributed to a wider temperature range, and the maximum intensity of flaming was muc

ISSN:0449-2994    

DOI:10.1002/polc.5070060109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractCrystallizing and melting of polymers as a function of sample history is investigated by means of a differential thermal analytic method developed for quantitative evaluation. Crystallization and the subsequent melting of the same polymer occur at temperatures differing by 12 to 18°C. The melt temperature and the time of keeping the sample in the molten state, the cooling rate and the course of cooling have a reproducible effect on the subsequent melting. The crystallization is followed at constant temperature, and the crystallization rate is evaluated. Application of the Avrami method gives agreement with similar density and refractive index measurements

ISSN:0449-2994    

DOI:10.1002/polc.5070060110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractThe crystallization of polypropylene has been studied by DTA in a linear thermal gradient type furnace. The crystallization rate was found to be linear with temperature, and the rate data were correlated on an Arrhenius type plot. The rate of crystallization of the low molecular weight fraction was lower at the same temperature than the rate for a higher molecular weight fraction.

ISSN:0449-2994    

DOI:10.1002/polc.5070060111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY

摘要:

AbstractBranched or partially chlorinated polyethylenes may be considered as copolymers, the branching or chlorinated sites forming the noncryatallizing components. Melting curves are calculated according to Flory and compared to experimental curves on well annealed samples. A normalized conversion (fitting) function is obtained which is largely independent of the nature and concentration of the noncrystallizing component. By means of the fitting function conclusions are possible on the deviation from tlier mo dynamic equilibrium, on the crystallite size distribution and on the heterogeneous small angle scattering behavior.

ISSN:0449-2994    

DOI:10.1002/polc.5070060112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1964

数据来源: WILEY