Synthesis and crystallization behaviors of poly(styrene-b-isoprene-b-epsilon-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene-b-isoprene-b-epsilon-caprolactone)s (PS-b-PI-b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS-b-PI-OH was synthesized by sequential- anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS-b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS-b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL27, PCL328 and PS-b-PI-b-PCL344 are 0.71, 0.46 and 0.07 mu m s(-1), respectively. The atomic force microscopy (AFM) images of the PS90-b-PI66-b-PCL-(28) show the columns morphology formed by it's self-assembling.

Miscibility, crystallization and mechanical properties of PPC/PBS blends

In this paper, melt blends of poly(propylene carbonate) (PPC) with poly(butylene succinate) (PBS) were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), tensile testing, wide-angle X-ray diffraction (WAXD), polarized optical microscopy and thermogravimetric analysis (TGA). The results indicated that the glass transition temperature of PPC in the 90/10 PPC/PBS blend was decreased by about 11 K comparing with that of pure PPC. The presence of 10% PBS was partially miscible with PPC. The 90/10 PPC/PBS blend had better impact and tensile strength than those of the other PPC/PBS blends. The glass transition temperature of PPC in the 80/20, 70/30, and 60/40 PPC/PBS blends was improved by about 4.9 K, 4.2 K, and 13 K comparing with that of pure PPC, respectively; which indicated the immiscibility between PPC and PBS. The DSC results indicated that the crystallization of PBS became more difficult when the PPC content increased. The matrix of PPC hindered the crystallization process of PBS. While the content of PBS was above 20%, significant crystallization-induced phase separation was observed by polarized optical microscopy. It was found from the WAXD analysis that the crystal structure of PBS did not change, and the degree of crystallinity increased with increasing PBS content in the PPC/PBS blends.

Primary and secondary crystallization kinetic analysis of nylon 1212

The isothermal and non-isothermal melt-crystallization kinetics of nylon 1212 were investigated by differential scanning calorimetry. Primary and secondary crystallization behaviors were analysed based on different approaches. The results obtained suggested that primary crystallization under isothermal conditions involves three-dimensional spherulite growth initiated by athermal nucleation, while under non-isothermal conditions, the mechanism of primary crystallization is more complex. Secondary crystallization displays a lower-dimensional crystal growth, both in the isothermal and non-isothermal processes. The crystallite morphology of nylon 1212, isothermally crystallized at various temperatures, was observed by polarized optical microscopy. The activation energies of crystallization under isothermal and non-isothermal conditions were also calculated based on different approaches.

Influence of shear on polypropylene crystallization kinetics

Isothermal crystallization kinetics under shear in the melt of iPP was investigated by optical microscopy. It appears that shearing from 200 to the crystallization temperatures enhanced the kinetics, but the shear effect was not obvious if the melt of iPP was sheared only at 200. The experiment results show that relaxation plays an important role during crystallization, and that spherulite growth rates increased with shear rates and were governed by relaxation. The effect of flow on the crystallization kinetics can be understood by considering that the increase of the degree of order due to flow results is an effective change of the melt free energy. The Laurizen-Hoffman theory and the DE-IAA model were used to describe the shear-induced crystallization kinetics of iPP excellently.

Miscibility and crystallization behavior of poly(3-hydroxyvalerate-co-3-hydroxyvalerate)/poly(propylene carbonate) blends

Blends of synthetic poly(propylene carbonate) (PPC) with a natural bacterial copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV) containing 8 mol % 3-hydroxyvalerate units were prepared with a simple casting procedure. PPC was thermally stabilized by end-capping before use. The miscibility, morphology, and crystallization behavior of the blends were investigated by differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffraction (WAXD), and small-angle Xray scattering (SAXS). PHBV/PPC blends showed weak miscibility in the melt, but the miscibility was very low. The effect of PPC on the crystallization of PHBV was evident. The addition of PPC decreased the rate of spherulite growth of PHBV, and with increasing PPC content in the PHBV/PPC blends, the PHBV spherulites became more and more open. However, the crystalline structure of PHBV did not change with increasing PPC in the PHBV/PPC blends, as shown from WAXD analysis. The long period obtained from SAXS showed a small increase with the addition of PPC.

Miscibility, crystallization kinetics, and morphology of poly(beta-hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(beta-hydroxybutyrate) (PHB) and poly(methyl acrylate) (PMA) were studied with differential scanning calorimetry, optical microscopy, and small-angle X-ray scattering (SAXS). As the PMA content increases in the blends, the glass-transition temperature and cold-crystallization temperature increase, but the melting point decreases. The interaction parameter between PHB and PMA, obtained from an analysis of the equilibrium-melting-point depression, is -0.074. The presence of an amorphous PMA component results in a reduction in the rate of spherulite growth of PRE. The radial growth rates of spherulites were analyzed with the Lauritzen-Hoffman model. The spherulites of PHB were volume-filled, indicating the inclusion of PMA within the spherulites. The long period obtained from SAXS increases with increased PMA content, implying that the amorphous PMA is entrapped in the interlamellar region of PHB during the crystallization process of PHB. All the results presented show that PHB and PMA are miscible in the melt. (C) 2000 John Wiley & Sons, Inc.

Effect of nucleating agent on the isothermal crystallization kinetics of PHBV

The crystallization behavior of PHBV, poly(beta -hydroxybutyrate-co-beta -hydrxyvalerate), with nucleating agents under isothermal conditions was investigated. A differential scanning calorimeter was used to monitor the crystallization process from the melt. During isothermal crystallization, the dependence of relative degree of crystallinity on time was described by the Avrami equation. It has been shown that the addition of BN and Tale causes a considerable increase in the overall crystallization rate of PHBV but does not influence the Avrami exponent n, mechanism of nucleation and spherulite growth mode of PHBV. A little of nucleating agent will increase the crystallization rate and decrease the fold surface free energy sigma (e), remarkably. The effect of BN is more significant than that of Talc.

Study on the properties of poly(beta-hydroxybutyrate) grafted with maleic anhydride

The thermal stability, crystallization behavior and biodegradability of poly(beta -hydroxybutyrate) (PHB) grafted with maleic anhydride (MA) were studied by DSC,TGA, optical microscopy and WAXD. The results showed that thermal stability of maleated PHB was obviously improved, comparing with that of pure PHB. The temperature of decomposition was enhanced about 20 degreesC After grafting MA, the crystallization behavior of PHB changed evidently. The rate of spherulite growth decreased, the crystallization temperature from the melt state reduced, and the cold crystallization temperature from the glass state increased. With the increase in graft degree, the banding texture of spherulite became more distinct and orderly. Moreover, the introduction of MA groups promoted the biodegradation of PHB.

Miscibility and crystallization of PHB PMA blends

The miscibility, crystallization behavior and morphological structure of PHB/PMA blends have been studied by the differential scanning calorimeter (DSC) and polarized optical microscopy (POM). The chemical repeat units of the two components of the blend are isomers. The results indicate that PHB and PMA are miscible in the melt. The addition of PMA into PHB results in a depression in the spherulite growth rate of PHB. With increasing PMA content in the blends, the texture of PHB spherulite becomes more open.

Miscibility and crystallization of poly(beta-hydroxybutyrate)/poly(vinyl acetate-co-vinyl alcohol) blends

Poly(vinyl acetate-co-vinyl alcohol) copolymers (P(VAc-co-VA)) were synthesized by hydrolysis-alcoholysis of PVAc. The miscibility, crystallization, and morphology of poly(P-hydroxybutyrate) (PHB) and P(VAc-co-VA) blends were studied by differential scanning calorimetry, optical microscopy (OM), and SAXS. It is found that the P(VAc-co-VA)s with vinyl alcohol content of 9, 15, and 22 mol % will form a miscible phase with the amorphous part of PHB in the solution-cast samples. The melting-quenched samples of PHB/P(VAc-co-VA) blends with different vinyl alcohol content show different phase behavior. PHB and P(VAc-co-VA9) with low vinyl alcohol content (9% mel) will form a miscible blend in the melt state. PHB and P(VAc-co-VA15) with 15 mol % vinyl alcohol will not form miscible blends while PHB/P(VAc-co-VA15) blend with 20/80 composition will form a partially miscible blend in the melt state. PHB and P(VAc-co-VA22) with 22 mol % vinyl alcohol are not miscible in the whole composition range. The single glass transition temperature of the blends within the whole composition range suggests that PHB and P(VAc-co-VA9) are totally miscible in the melt. The crystallization kinetics was studied from the whole crystallization and spherulite growth for the miscible blends. The equilibrium melting point of PHB in the PHB/P(VAc-co-VA9) blends, which was obtained from DSC results using the Hoffman-Weeks equation, decreases with the increase in P(VAc-co-VA9) content. The negative value of the interaction parameter determined from the equilibrium melting point depression supports the miscibility between the components. The kinetics of spherulitic crystallization of PHB in the blends was analyzed according to nucleation theory in the temperature range studied in this work. The best fit of the data to the kinetic theory is obtained by employing WLF parameters and the equilibrium melting points obtained by DSC. The addition of P(VAc-co-VA) did not affect the crystalline structure of PHB, as shown by the WAXD results. The long periods of blends obtained from SAXS increase with the increase in P(VAc-co-VA) content. It indicates that the amorphous P(VAc-co-VA) was rejected to interlamellar phase corporating with the amorphous part of PHB.

Crystallization kinetics and morphology of poly(beta-hydroxybutyrate) and poly(vinyl acetate) blends

The crystallization behavior and morphology of poly(beta-hydroxybutyrate) and poly(vinyl acetate) blends have been studied with DSC, POM, SAXS and WAXD methods. The results indicate that the overall crystallization rate and spherulite growth rate are slower in the blends than that in the pure PHB. The addition of PVAc has no effect on the crystal structure of PHB, but affects its crystalline morphology. During crystallization of PHB, PVAc chains were being rejected into the region between the lamellae of crystalline PHB. (C) 1997 Elsevier Science Ltd.

Miscibility and crystallization of poly(beta-hydroxybutyrate) and poly(p-vinylphenol) blends

The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB) and poly(p-vinylphenol) (PVPh) blends were studied by differential scanning calorimetry and optical microscopy (OM). The blends exhibit a single composition-dependent glass transition temperature, characteristic of miscible systems, A depression of the equilibrium melting temperature of PHB is observed. The interaction parameter values obtained from analysis of the melting point depression are of large negative values, which suggests that PHB and PVPh blends are thermodynamically miscible in the melt. Isothermal crystallization kinetics in the miscible blend system PHB/PVPh was examined by OM. The presence of the amorphous PVPh component results in a reduction in the rate of spherulite growth of PHB. The spherulite growth rate is analyzed using the Lauritzen-Hoffman model, The isothermally crystallized blends of PHB/PVPh were examined by wide-angle X-ray diffraction and smell-angle X-ray scattering (SAXS). The long period obtained from SAXS increases with the increase in PVPh component, which implies that the amorphous PVPh is squeezed into the interlamallar region of PHB.

The effects of ionising radiation on polypropylene

The interaction of ionising radiation with polymers is described and the literature relating; to the effects on polypropylene is reviewed. Oxidative and free radical reactions are discussed with particular reference to post-irradiationeffects.Isotactic and atactic polypropylene were δ and electron irradiated to doses of up to 20 megarad. Irradiations weremainly made in air. A series of other polymers were also irradiated in a preliminary survey. Molar mass measurements are used to measure the radiationyield for chain scission G (s). Irradiation at room temperature causes significantly more chain scission than at 195K. Additional chain scission occurs on storage following irradiation at 195 K. Free radical concentrations are determined by electron spin resonance, and the decay rates measured. The radical formed in air is a peroxy radical and in vacuo is a hydrocarbon radical. At77K in vacuo the radical is -CH2 - C* (CH3) - CH2 - but additional radicals are produced on warning to room temperature. The effects of increasing tenparature on radicals formed in air are described. Electron spin resonance studies on atactic polypropylene,and isotactic polypropylene in hydrogen, sulphur dioxide and nitric oxide are reported.. The melting temperatures, spherulite growth rates, and isothermal crystallisation rates of irradiated polypropylene are compared to those of the non-irradiated polymer. Crystallisation is found to proceed with an Avrami integer n = 2. At a given crystallisation temperature, the overall crystallisation rate of irradiated polymer is less than the non-irradiated, but spherulite growth rates are identical. Thermogravimetric analysis is used to assess the thermal stability of irradiated polypropylene in nitrogen, air and oxygen. Hydroperoxide analysis is used to show that several molecules of oxygen are absorbed for each initial radical, and that hydroperoxides continue to be formed for a long period following irradiation. Possible solutions for minimising irradiation and post-irradiation degradation are suggested, together with some problems for further study.

The study of banded spherulite patterns by coupled logistic map lattice model

Banded spherulite patterns are simulated in two dimensions by means of a coupled logistic map lattice model. Both target pattern and spiral pattern which have been proved to be existent experimentally in banded spherulite are obtained by choosing suitable parameters in the model. The simulation results also indicate that the band spacing is decreased with the increase of parameter mu in the logistic map and increased with the increase of the coupling parameter epsilon, which is quite similar to the results in some experiments. Moreover, the relationship between the parameters and the corresponding patterns is obtained, and the target patterns and spiral patterns are distinguished for a given group of initial values, which may guide the study of banded spherulite.

Rhythmic growth of ring-banded spherulites in blends of liquid crystalline methoxy-poly(aryl ether ketone) and poly(aryl ether ether ketone)

Rhythmic growth of ring-banded spherulites in blends of liquid crystalline methoxy-poly(aryl ether ketone) (M-PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring-banded spherulites in the M-PAEK/PEEK blends is strongly dependent on the blend composition. In the M.-PAEK-rich blends, upon cooling, an unusual ring-banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M-PAEK/PEEK blend, ring-banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M-PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring-banded spherulite formation in the blends. In addition, the effects of M-PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed.