Growth transition and morphology change in polypropylene

Abstract

Abstract:The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 ~ and interpreted as a Regime III --* Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II ~ Regime I transition is also theoretically predicted at 155 ~ i. e. at a temperature outside the investigated temperature range. The Regime III --, Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at Tc < 138 ~ (Regime III) and preferentially radiating lameUae at Tc > 138 ~ (Regime II). It is suggested that such a morphological change could be interpreted using the concept of "nonadjacent re-entry" introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites.

Direct correlation between modulus and the crystalline structure in isotactic polypropylene

“…The samples were heated up to 220°C and held there in order to eliminate the thermal and mechanical prehistory. The crystallinity of the samples was determined based on the melting curve recorded during first heating according to Equation (1): [28]. The SIST experiments were carried out on the same equipment between 160 and 100°C.…”

Physical state of the amorphous phase of polypropylene-influence on thermo-mechanical properties

“…As presented based on X-ray measurements the thickness of crystals in the reference and modified samples (irrespective of the method of modification) was almost identical (6.8 nm for RP, 6.8 nm for SSn, 6.7 nm for MSn). Meanwhile, the value of this parameter determined on the basis of aforementioned equation (the following values were taken for calculations: s e ¼ 62.3 Â 10 À7 J/cm 2 , T mo ¼ 208 C [48], H f ¼ 209 J/g [36], and r c ¼ 0.936 g/cm 3 ) in case of the systems containing the modifier would be substantially lower (6.6 nm for SSn, 6.4 nm for MSn) than in case of the reference material (7 nm). The shift of melting temperature of polypropylene/modifier systems can be also induced by a change of the fold surface energy, s e , of polypropylene lamellar crystals caused by the presence of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64infused modifier molecules near fold surface of crystals but not their reorganization.…”

Determination of Nucleus Density in Semicrystalline Polymers from Nonisothermal Crystallization Curves

“…We may note that the time and temperature points are equivalent using a constant cooling rate and every point of the DSC curve can be given as a function of time or temperature. ∆ is the partial crystallization enthalpy at t time, m is the sample mass, ∆ 0 is the equilibrium enthalpy of fusion 36 and its value is 148 Jg -1…”