Blends of the β‐modification of polypropylene

Varga, J.; Schulek-Tóth, F.; Mudra, István

doi:10.1002/masy.19940780120

Cited by 26 publications

(19 citation statements)

References 6 publications

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“…19,22 These results indicate that two growth rate intersections appear on temperature dependence of spherulite growth rate curves for and forms. In fact, two crossover points are observed clearly by the present work as seen in Figure 1, defining three temperature regions, below 90 C (lower crossover), between 90 C to 133 C and above 133 C (higher crossover) marked as A, B and C. These crossover points coincide with reference data, [17][18][19][20][21][22] except for their actual temperatures. The present crossover temperatures are 7-15 C lower than those from references.…”

Section: Resultssupporting

confidence: 75%

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Temperature Dependence of Crystal Growth Rate for α and β Forms of Isotactic Polypropylene

Nakamura

Shimizu

Umemoto

et al. 2008

Polym J

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The crystal growth rate of the 1 , 2 and forms of isotactic polypropylene (iPP) and their morphological changes were studied in a wide range of crystallization temperatures. The temperature dependence of the crystal growth rate of the 1 form showed a bell-shaped curve with the maximum growth rate (G max ) at 70 C. The crystal growth rate of the form induced by calcium pimelate also showed a bell-shaped curve with G max at 79 C. Two crossover points on the growth rate curve from the 1 form to the form or vice versa were observed at 90 C and 133 C, respectively. Tear-drop shaped spherulites were observed at temperatures between the two crossover points. Electron diffraction patterns showed the high ordered structure of the 2 form for thin films crystallized at 140 C. The 2 fraction became detectable in X-ray diffraction pattern for temperatures above 110 C. The 2 fraction increased with crystallization temperature and saturated to 100% at about 140 C. In the temperature region from 110 C to 140 C, several crystal growth rates were found at the same crystallization temperature. The growth rate variations could be associated with the co-crystallization of the 1 and 2 forms. Above 140 C, the growth rate variations disappeared, since the fraction of the 2 reached to 100%. The extrapolated G max of the 2 showed at 72 C.KEY WORDS: Isotactic Polypropylene / -Form / -Form / Crystal Growth Rate / Crossover / Isotactic polypropylene (iPP) is one of the most widely used commercial polymeric materials and has been extensively investigated for it academic and industrial interest. iPP displays different structural polymorphism, such as form (monoclinic), form (trigonal), form (orthorhombic) and smectic form, which all consist of 3 1 helical conformations with a 0.65 nm chain axis periodicity. The form is the most common crystal structure, which is produced by crystallization from the melt or solution.1-5 The form can be obtained from temperature gradient crystallization, 6 crystallization under molecular orientation 7 or can be induced by selective -nucleating agent. 8-10The crystal structure of the form was first determined by Natta and Corradini. 11 Mencik 12 and Hikosaka and Seto 13showed that the structure has two limiting modifications named 1 and 2 forms. Extensive works on these crystalline forms have been also reported. 14-16 The 1 form space group (C2/c) is the limit-disordered structure and the 2 form (P2 1 /c) is the limit-ordered structure. They are characterized by either regular alternation of the up and down orientations of the methyl group along the chain ( 2 ) or random orientation. A transition from the 1 form to the 2 form is observed by annealing at a higher temperature. [17][18][19][20][21][22] The crystal structure of the form has been analyzed by Meille et al. 23 and refined by D. L. Dorset et al. 9Many studies about the crystallization behavior and morphology of iPP have been reported. When iPP was crystallized from the melt in a wide temperature range, Keith and Padden found four distinct spherulites,...

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Section: Resultssupporting

confidence: 75%

“…A transition from the 1 form to the 2 form is observed by annealing at a higher temperature. [17][18][19][20][21][22] The crystal structure of the form has been analyzed by Meille et al 23 and refined by D. L. Dorset et al …”

mentioning

confidence: 99%

Temperature Dependence of Crystal Growth Rate for α and β Forms of Isotactic Polypropylene

Nakamura

Shimizu

Umemoto

et al. 2008

Polym J

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“…Ca salts, which were precipitated as a fine white powder, were filtered, washed with ethanol, and dried in a vacuum at room temperature. 7 The SEM records showed similar agglomerates of crystalline lamellae for both nucleating agents (Fig. 1).…”

Section: Preparation and Characterization Of New ␤-Nucleating Agentsmentioning

confidence: 68%

Highly active thermally stable ?-nucleating agents for isotactic polypropylene

Varga

Mudra

Ehrenstein

1999

J. Appl. Polym. Sci.

240

142

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Calcium salts of suberic (Ca-Sub) and pimelic (Ca-Pim) acids were synthesized and implemented as in different grades of isotactic polypropylene (iPP). Propylene homopolymer, as well as random and block copolymers containing these additives, crystallized iPP into pure or nearly pure ␤ modification in the isothermal and nonisothermal crystallization experiments. Recently, Ca-Sub proved to be the most effective ␤-nucleating agent of iPP. The Ca-Sub nucleating agent widens the upper crystallization temperature range of pure ␤-iPP formation up to 140°C. In this study the effect of the these additives on the crystallization, melting characteristics, and structure of the PP were studied. The degree of crystallinity of ␤-iPP was markedly higher than that of ␣-iPP. A widening in the melting peak of the samples crystallized in a high temperature range was first observed and discussed in regard to literature results of the same phenomenon for ␣-iPP. The morphology of the ␤-iPP samples was revealed by scanning electron microscopy. Independent of the type of polymer or nucleating agent, hedritic structures were found in the early stages of growth of the ␤-spherulites.

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“…Dehydrated calcium pimelate was used as the nucleating agent to produce the ␤ modification of iPP. 26 The concentration of the nucleating agent added to the polymer was between 0.01 and 0.5 wt %. Flat, sheetlike polymer samples 100 m and 45 m thick were produced by isothermal crystallization at 140 and 143°C in a Mettler hot stage, respectively.…”

Section: Methodsmentioning

confidence: 99%