CRYSTALLIZATION BEHAVIOR OF CROSS-LINKED GRAFTS OF POLYPROPYLENE
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The cross-linked grafts of polypropylene with high grafting levels and polarity were prepared from isotactic polypropylene (iPP) reacting with maleic anhydride (MAH) and triallyl isocyanurate (TAIC) in solid phase. Rheological characteristic, crystallization and melting behavior, and crystal morphology of the grafts were studied. Addition of TAIC during reaction makes the molecular structure of PP stable and the molten viscosity increases significantly. The crystallization peaks, melt temperatures, crystallinity and crystallization rates of the grafted PP are lower compared to pure PP. But the nucleating ability of the cross-linked graft with higher grafting level is strongest, and the behavior of isothermal crystallization is different from that of PP and MPP. Its nucleation and growth mechanism is two-dimensional growth of crystallites from instantaneous nucleation.Keywords:
Tacticity
Maleic anhydride
Polypropylene
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Abstract The influence of a nucleating agent, lanthanum stearate (LaSt), on the crystallization behavior of isotactic polypropylene (iPP) was investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide‐angle x‐ray scattering (WAXD). It was found that LaSt can act as a β‐nucleating agent and induce the formation of a high content of β‐form during the crystallization of iPP. The content of β‐form is greatly affected by crystallization temperature and cooling rate. High crystallization temperature and low cooling rate are favorable to the formation of β‐form. The results of isothermal crystallization kinetics show that LaSt shortens the crystallization half time ( t 1/2 ) and accelerates the crystallization of iPP. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Tacticity
Lanthanum
Polypropylene
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The crystallization and melting behavior of isotactic polypropylene (iPP) and polypropylene copolymer (co-PP) containing silicon dioxide (SiO2) were investigated using differential scanning calorimeter (DSC) and X-ray diffraction. SiO2 had a heterogenous nucleating effect on iPP, leading to a moderate increase in the crystallization temperature and a decrease in the half crystallization time. Because of the large surface area and high surface free energy, SiO2 particles are able to absorb the short segments with low isotacticity of co-PP on the surface and thus restrict the mobility of the chains, leading to the decrease of crystallization temperature. It was observed that SiO2 particles inhibited the generation of β form crystal in iPP. However, the relative proportions of various α crystal forms in co-PP were not obviously changed with the addition of SiO2 particles.
Tacticity
Polypropylene
Crystal (programming language)
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Maleic zinc was successfully grafted on polypropylene powder by solid-phase grafting technology.The crystallization behavior of PP and its graft copolymers was studied by WAXD,PLM and DSC.The results indicate that the graft group can induce PP to form β type crystal,and its spherulite become smaller and imperfect.The graft copolymers are easy to crystallize at higher temperature.The isothermal crystallization kinetics indicate that the graft group can accellerate the crystallization rate of PP,and doesn`t affect the nucleation behavior.
Spherulite (polymer physics)
Polypropylene
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The kinetics of isothermal crystallization has been studied for Na +,Mn 2+ and Ca 2+ ionomers based on maleic anhydride graft polypropylene(PP g MAH) by DSC,compared with pure PP and PP g MAH.Avrami equation was valid for analyzing the experimental data.The fact that Avrami exponents close to three for all the samples implied the mode of PP crystallization was not changed by the solid graft modification.The introduction of ions increased the crystallization rate(characterized by the reciprocal of the half life of the crystallization, t -1 1/2 ) dramatically.At the same time,the increase of neutralization also increased the crystallization rate. The reducing of the interfacial free energies of the side surfaces of the nucle σ e,calculated from Hoffman theory,by the anhydride group and ions had the same trend with the results of Avrami equation.
Maleic anhydride
Avrami equation
Polypropylene
Isothermal process
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Polypropylene
Isothermal process
Small-angle X-ray scattering
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Citations (149)
Non-isothermal crystallization behavior of reactor-made polypropylene (PP) copolymer with or without a nucleating agent and/or nano-calcium carbonate was investigated by means of differential scanning calorimeter (DSC). The results show that PP copolymer with the nucleating agent exhibites a higher crystallization temperature, a slightly higher crystallization rate in terms of the half time and a lower degree of crystalline. But addition of nano-calcium carbonate to PP copolymer greatly increased crystallization temperature and crystallization rate, and degree of crystalline is increased by about 10%, thus being in favor of improving mechanical properties. The Ozawa theory and Caze method were employed to describe the non-isothermal crystallization kinetics.
Polypropylene
Isothermal process
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The isothermal crystallization behavior of neat polypropylene (PP) and solid-phase graft copolymers of PP with maleic anhydride and methyl methacrylate (PPMM) were compared by differential scanning calorimetry. The Avrami equation and Hoffman theory were applied to describe the isothermal crystallization kinetics. The results show that the fitted isothermal crystallization parameters are similar to the experimental data, and suggest that the Avrami equation is suitable to describe the isothermal crystallization process of PP and PPMM. The grafted side chains on PP can change the nucleation and growth of crystallization. They caused a decrease in the apparent crystallization activation energy and lateral surface free energy, and an increase in the nucleation rate. This was attributed to the grafted side chains not only acting as nucleating agent but also hindering the motion of the molecular chains and reducing the growing rate of crystallization.
Maleic anhydride
Polypropylene
Avrami equation
Isothermal process
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PP/PS blends modified by grafted PP and reactive monomer were prepared by twin screw extruder. The crystallization and melt behavior of modified blends were investigated by DSC. Three reactive monomers, AA- g-PP and MA- g -PP were used as modifying agent. The results indicated that addition of PS increased the crystallization temperature of PP. AA- g -PP and MA- g -PP further increased the crystallization temperature of PP in its blends. Although reactive monomer at low content slightly aecreased the crystallization temperature of PP in the blends, the addition of styrene at high content increased the crystallization temperature of PP. All blends show no remarkable variety in melt temperature, but the shapes of melt peak is influenced by crystallization temperature.
Reactive extrusion
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Linear polypropylene was blended with low-density polyethylene,and the crystallization behavior was studied by DSC/POM.It showed that low-density polyethylene could decrease the peak crystallization temperature and the absolute crystallinity of linear polypropylene,however,the melt behavior was slightly affected.Moreover,the non-isothermal crystallization kinetics study showed that low-density polyethylene could also increase the amount and reduce the size of spherulites by changing the crystallization nucleation behavior of linear polypropylene.As a consequence,the foaming potentiality of the blends was enhanced.
Polypropylene
Linear low-density polyethylene
Isothermal process
Low-density polyethylene
High-density polyethylene
Spherulite (polymer physics)
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The isothermal crystallization behavior of PP-g-MAH was measured using differential scanning calorimetry(DSC) and the kinetics of isothermal crystallization was analyzed with Avrami equation.Effects of MAH grafting ratio,the extent of PP degradation,and the structure of grafting comonomers on the kinetics of isothermal crystallization of PP-g-MAH were examined.The MAH groups grafted onto PP could promote the formation of nucleation rate,giving rise to an increased crystallization rate.However,the enhanced intermolecular force,from the high degree of MAH grafting ratio,restricted the segment motion and resulted in the slowing down of the crystallization process.The isothermal crystallization of PP-g-MAH was controlled by the nucleation rate at high temperature region,and as a result,the crystallization rate of PP-g-MAH decreased as the extent of PP degradation during the melt grafting process increased.When divinyl benzene was used as the grafting comonomer,the rigid group and the possible micro-crosslinking structure hindered the crystallization.
Maleic anhydride
Polypropylene
Isothermal process
Avrami equation
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