摘要:

Low-density polyethylene (LDPE) films irradiated with fast electrons within the range of irradiation doses 0-40 Mrad have been studied by means of WAXS and SAXS. The degree of crystallinity, the total intensity of WAXS, and the dimension of the mosaic blocks in the [110] and [200] directions have been found to be almost independent of the irradiation dose. The SAXS parameters (long period, lamella thickness, intensity of scattering from the diffuse and the discrete regions, total intensity) depend on the dose in the same way. A parallel has been made between the x-ray and the calorimetric degree of crystallinity. The latter shows a threefold greater decrease with the increase of the dose, in comparison with the former. The average dimensions of the scattering particles, as well as the difference between the crystalline and the amorphous density (ρc-ρa), do not change with the increase of the irradiation dose. The data obtained lead us to the conclusion that the irradiation of LDPE films with fast electrons at low doses results in the formation of a nonhomogenous network. The points of crosslinking are localized within the amorphous phase and the surface nonarranged regions of the crystallites. It has been shown that the partial crosslinking of the crystalline phase does not significantly affect the polymer's crystallinity, but does affect the thermodynamic heat of melting. The lower enthalpy of melting of the crosslinked films, whose degree of crystallinity stays almost constant, has been explained by the increase of the surface free energy of the crystallites as a result of crosslinking within the noncrystalline surface regions of the lamellae.

ISSN:0022-2348    

DOI:10.1080/00222348808212309

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Interchange reactions taking place at high temperatures in phenoxy/poly(butylene terephthalate) blends have been studied by differential scanning calorimetry. Results show the influence that these types of reactions have on the thermal transitions of the blends. These results may be explained on the basis of a reaction between hydroxyl groups in phenoxy and ester groups of poly(butylene terephthalate), causing the formation of grafted and crosslinked copolymers.

ISSN:0022-2348    

DOI:10.1080/00222348808212310

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Phase compatibility of nylon 66 in mixtures with polyethylene of various compositions and concentrations was investigated. Optical microscopy and thermal analysis verified incompatibility, predicted by theory, in concentrations as low as 1 wt% polyethylene, regardless of type and molecular weight (melt index). Although incompatible, mixtures in this range are of importance in various industrial applications where, typically, the polyethylene component serves as carrier for pigments and additives.

ISSN:0022-2348    

DOI:10.1080/00222348808212311

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper considers the geometric aspects of the shear deformation of highly drawn linear polyethylene sheets parallel to the principal orientation direction, concentrating on the morphological aspects relating to the deformation, in terms of both the initial drawing and the subsequent shear. It relates directly to previous studies of the shear strength and mechanical behavior of these materials.

ISSN:0022-2348    

DOI:10.1080/00222348808212312

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Strain-induced crystallization (SIC) is studied in blends of cis-1, 4-polyisoprene (Hevea rubber) and synthetic trans-1, 4-polyisoprene (t-PI). Uncrosslinked solution blends were uniaxially stretched at room temperature, and the dependence of stress and birefringence on time, elongation, and t-PI content was analyzed. Stress and birefringence follow power-law decays. The rates of relaxation decrease with elongation and t-PI content, and the rates of stress relaxation are higher than the rates of birefringence relaxation for the blends studied here. At high elongation, stress- and birefringence-strain plots exhibit the drastic increase ascribed to strain-induced crystallization. With increasing amounts of t-PI, the onset of the SIC phenomenon occurs at smaller elongations.

ISSN:0022-2348    

DOI:10.1080/00222348808212313

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

LDPE films irradiated with fast electrons at doses in the range 0-40 Mrad have been investigated by DSC and thermomechanical methods. The irradiated films do not flow in the melt state. The temperature of melting of the films does not change with the radiation dose. The material which is obtained as a result of melting possesses high elasticity. The modulus of compression changes proportionally to the radiation dose. The enthalpies of melting and crystallization of the irradiated films decrease with increasing of the radiation dose. LDPE films that had been melted and recrystallized were characterized by the same methods. The properties of these materials were similar. Only the melting temperature decreased slightly. Thermodynamical considerations about the phase transition behavior of the crosslinked LDPE are discussed. The conclusions are the following: The irradiation of the films results in crosslinking predominantly in the amorphous regions, the crystalline regions being only slightly affected. The degree of crosslinking does not affect the temperature of melting of the crystalline phase, although it influences the enthalpy of melting and the thermomechanical properties of the film.

ISSN:0022-2348    

DOI:10.1080/00222348808212314

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The relative strength of hydrogen bonds formed by H2O and D2O was compared directly by measuring the tensile strength of strips of pure cellulose paper immersed in liquid water, heavy water, and a 1:1 mixture. The wet strength of paper was 8% lower in H2O than in D2O and intermediate in the mixture. The cohesion of paper is due to intrafiber and interfiber hydrogen bonds between cellulose chains. Water weakened the paper somewhat more than heavy water did because it forms somewhat stronger hydrogen bonds with the hydroxyl and ether groups of cellulose and, therefore, broke more interfiber hydrogen bonds.

ISSN:0022-2348    

DOI:10.1080/00222348808212315

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor