摘要:

Composite films of polyethylene with ultrahigh molecular weight (6 × 106) and corn starch were prepared by gelation-crystallization from dilute solutions. The polyethylene-starch compositions chosen were 3/1, 1/1, 1/3, and 1/5. The elongation was carried out in a hot oven at 135°C. The maximum drawability was affected by the composition. The maximum draw ratios of the 1/5 composite reached 80, and the corresponding Young's modulus was 10 GPa. The values of the films with the 3/1 and 1/1 composites were about 75 and 105 GPa, respectively, which are higher than the moduli of aluminum(70 GPa) and cast iron (90 GPa). In spite of the elongation up to such high draw ratios, most starch particles remained within the composite films. This interesting phenomenon is discussed in terms of the morphology of the composite films as studied by wide-angle x-ray diffraction, small-angle x-ray scattering, and scanning electron microscopy. Furthermore, the composite films with different compositions were put on a decarbonized agarose bench containing mineral nutrients, which had been prepared as isolate filamentous fungi medium in a Petri dish. Then two kinds of filamentous fungi,Myrothecium verrucariaIFO 6531 andChaetomium globosumIFO 6347, were put on each film for 25 days. Observation by scanning electron microscopy revealed that the number of starch particles in the fibrous tissue decreased, and the sizes of residual particles were much smaller than the original sizes, indicating the biodegradation of starch by the filamentous fungi. This tendency is significant forM. verrucaria. Disruption of the polyethylene fibrous textures could not be confirmed by scanning electron microscopy, in spite of the decrease in Young's modulus and tensile strength in comparison with those of the original specimens.

ISSN:0022-2348    

DOI:10.1080/00222349608220401

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A method for the determination of equilibrium melting temperature from induction time measurements is suggested. Theory of the induction time,ti(most probable period from the beginning of isothermal crystallization to the instant when a stable crystal nucleus starts growing) involves parameters that influence the nucleation-crystallization process, such as specific interfacial free-energy parameter, specific surface energies of a growing nucleus, enthalpy of crystal melting, diffusion activation energy, undercooling and the equilibrium melting temperature,Tm°. An extrapolation method exploiting the aspect of the induction time that it increases to infinity, that is, 1/tidecreases to zero at the equilibrium melting temperature, cannot be used to calculate the equilibrium melting temperature. High- or low-temperature approximations of the basic equation yield some simplifications that make it possible to find its parameters via the best fit of the equation with experimental data. This procedure can yield also the value of the equilibrium melting temperature if the measured data are sufficiently precise. Applying that procedure to crystallization data of isotactic polypropylene, we obtained the values of the equilibrium melting temperatures 199.5°C (high-temperature approximation) and 212.7°C (low-temperature approximation). A more detailed discussion of the procedure suggests that from both these reasonable values, the higher one is more justified. This result agrees well with higherTm°data reported in the literature.

ISSN:0022-2348    

DOI:10.1080/00222349608220402

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0022-2348    

DOI:10.1080/00222349608220380

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor