Paracrystalline character of melt‐quenched isotactic polypropylene

Isotactic polypropylene films, Buplen Type, 40t2m thick, irradiated by a 6~ source to doses 0.37-37 Mrad, are investigated by means of optical microscopy, WAXS, thermogravimetry, DSC and DTA. The original film exhibits a paracrystal structure. Irradiation does not change the films' structure. The kinetic parameters of the non-isothermal destruction and the thermodynamic parameters of melting are obtained. The samples irradiated to small doses (up to 3 Mrad) are thermally more stable; the activating energy of the destruction is higher than that of the original film. The temperature of melting slightly increases, while the enthalpy of melting decreases. For the range of doses of 3.7-37 Mrad, the films show low thermal stability and the destruction proceeds with low activating energy. From the results of the data obtained, the following assumptions are made: the p-irradiation causes simultaneous crosslinking and chain scission at random sites along the chains. Fragments of partially crosslinked molecules and fractions of low molecular linear segments are formed. The destruction caused by radiation prevails above 3 Mrad.

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“…la) [16]. The WAXS diffractogram exhibited the characteristic diffusion reflexes at 20 = 16 ~ and 22 ~ for the paracrystal structure ( Fig.…”

Section: Resultsmentioning

confidence: 92%

Thermogravimetry and differential scanning calorimetry of ?-irradiated i-polypropylene films

Minkova

Lefterova

Koleva

et al. 1988

Colloid & Polymer Sci

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“…2 • 3 However, the probability of radical combination is dependent on polymer morphology, especially for crystalline and semicrystalline polymers. 4 Although photooxidative degradation of elastomeric ethylene-propylene copolymers has been the subject of several studies, 5 -7 little attention has been paid to heterophasic thermoplastic ethylene-propylene copolymers. The present study was carried out to examine t N.C.L.…”

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confidence: 99%

Effect of UV Irradiation on The Structure of Heterophasic Ethylene-Propylene Copolymers

Ramanathan

Singh

Sivaram

et al. 1994

Polym J

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ABSTRACT:Changes in [17] and crystallinity of commercial samples of isotactic polypropylene (i-PP), heterophasic ethylene-propylene copolymers [E-P copolymer] containing < 16mol% of ethylene and their fractions (having ethylene content 40.9 and 55. 7 mo!%) upon polychromatic irradiation in air at 55°C were studied by comparing unirradiated samples. Crystallinity was evaluated by DSC and X-ray diffraction. Viscosity results showed a decrease of molecular weight upon irradiation. DSC and X-ray studies revealed that the transition of ex-modification to /I-phase of polypropylene and also that crystallinity of the copolymer decreased initially upon irradiation. However, upon longer irradiation, the crystallinity increased again.

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“…The absorbance bands at 1168 and 974cm -1 are pseudocrystalline peaks. The ratio A l168/A974 is proportional to the helicoidally ordered portion of PP [13]. Relaxation (by change of this ratio after stopping the fatigue experiment) is detectable but hardly differentfrom the small relaxation always present when an elastomer sample is compressed between the ATRcrystal and the metal backing plate.…”

Section: Ftirmentioning

confidence: 99%

Evaluation of an elastomer for biomedical use in load-bearing applications

Helsen

Jaecques

Humbeeck

et al. 1993

J Mater Sci: Mater Med

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The fatigue behaviour of a medical-grade thermoplastic polyolefin (TPO) was investigated with the objective of using TPOs for endoprosthetical aims in dental and orthopaedic applications. For this purpose, a TPO was subjected to the combined action of shear and compression fatigue while in contact with Hanks' solution. Cyclic loading between 150 and 1500 kPa shear stress and a number of cycles up to 9 × 106 was applied. The potential fatigue damage was assessed by in-fatigue-recording of the mechanical hysteresis curves and, after fatigue, by swelling tests in acetic acid solutions, dynamic mechanical thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The combined and critical application of these techniques allowed us to conclude that this material exhibits a very satisfactory fatigue behaviour under the loads investigated, making this material potentially useful for endoprostheses. Moreover, biomedical prescreening tests (according to USP Class VI) were all negative, stimulating continued research on this type of material.

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Paracrystalline character of melt‐quenched isotactic polypropylene

Cited by 13 publications

References 7 publications

Thermogravimetry and differential scanning calorimetry of ?-irradiated i-polypropylene films

Thermogravimetry and differential scanning calorimetry of ?-irradiated i-polypropylene films

Effect of UV Irradiation on The Structure of Heterophasic Ethylene-Propylene Copolymers

Evaluation of an elastomer for biomedical use in load-bearing applications

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