不相容PHBV/PS、PHBV/PMMA结晶/非晶共混体系的结晶行为研究

在不同的共混比例、不同的结晶温度下对不相容PHBV/PS、PHBV/PMMA结晶/非晶共混体系的结晶行为做了系统的研究.研究发现当PHBV含量为75wt%时,共混体系仍然和纯PHBV一样生成环带球晶;而当PHBV含量为50wt%时,共混体系在略低于非晶组分玻璃化转变温度时呈现花瓣状的球晶形貌;当PHBV含量为25wt%时,PHBV/PS体系出现不规则的晶体形貌,而PHBV/PMMA体系在偏光显微镜下没有观察到晶体.在这种不相容共混体系中,非晶组分的分散状态以及共混比例对共混体系中PHBV环带球晶的形成起到决定性的作用,而非晶组分对PHBV球晶的片晶前端生长的影响是形成花瓣状球晶的主要原因.     

Effects of miscible diluent of poly(ether imide) on ring-banded morphology of poly(trimethylene terephthalate)

The melting, crystallization, and self-packed ring patterns in the spherulites of miscible blends comprising poly(trimethylene terephthalate) (PTT) and poly(ether imide) (PEI) were revealed by optical, scanning electron microscopies (PLM and SEM) and differential scanning calorimetry (DSC). Morphology and melting behavior of the miscible PTT/PEI blends were compared with the neat PTT. Ringed spherulites appeared in the miscible PTT/PEI blends at all crystallization temperatures up to 220 °C, whereas at this high temperature no rings were seen in the neat PTT. A postulation was proposed, and interrelations between rings in spherulites and the multiple lamellae distributions were investigated. The specific interactions and the segregation of amorphous PEI were discussed for interpreting the morphological changes of 220 °C-melt-crystallized PTT/PEI samples. Interlamellar segregation of PEI might be associated with multiple lamellae in the spherulites of PTT/PEI blends; therefore, rings were more easily formed in the PTT/PEI blends at all crystallization temperatures. A postulated model of uneven lamellar growth, coupled with periodical spiraling, more properly describes the possible origin of ring bands from combined effects of both interactions and segregation between the amorphous PEI and PTT in blends.     

Crystalline Morphology and Crystallization Characteristics of In-situ Blends of Anionic Polyamide 6 with Noncrystallizable Semiaromatic Polyamide Copolymer

A noncrystallizable semiaromatic polyamide copolymer(NSAP) was dissolved in molten caprolactam, and PA6/NSAP blends were produced in-situ via the anionic ring-opening polymerization of caprolactam. The presence of a single loss tangent(tanδ) peak measured by means of dynamic mechanical analysis(DMA) proves the miscibility between PA6 and NSAP in the blends. It was found that there existed drastic changes in the crystallographic form and crystallization kinetics for the in-situ blends, e.g., when 20% NSAP was added, nearly all crystallites existed in the γ form and the crystallization could hardly occur upon cooling even at a rate of 2.5 ℃/min. Moreover, cold crystallization appears during the subsequent heating, and its melting point is 40 ℃ lower than that of the virgin system. On the other hand, the size of the spherulites only decreases modestly. It is suggested that the introduction of irregular stiff segments originated from NSAP into PA6 macromolecule chain, which resulted from transamidation during the polymerization play a dominant role in the drastic change of crystallization kinetics and the resultant morphology of the in-situ blends.     

The crystallization and morphology of melt-miscible polymer blends

The morphology and kinetics of crystallization from melt-miscible blends is reviewed for binary systems in which either one or both polymer components are crystallizable. In systems in which one component (component A) crystallizes first, the other component (B) may reside finally between spherulites, between growth arms (composed of a stack of A crystalline lamellae), or between crystal lamellae of A. The kinetics of component redistribution dictates which site must become primary. It is shown that the diffusivity D of the components in the melt and the velocity V of spherulite growth combine through the diffusion length δ = D/V to define the final location for component B and to also define whether spherulite propagation will be linear or parabolic in time. When crystallization of both components proceeds concurrently, by forming spherulites of A and of B, the spherulites are prone to interpenetrate or to form concentric spherulites. Cooperative crystallization, in which the kinetics of a rapidly crystallizing component and a slowly crystallizing component are both affected such that the two crystallize nearly simultaneously, is discussed. Finally, the competition between liquid-liquid phase separation and crystallization in systems with either an upper or lower critical solution temperature is reviewed.     

On the macro- and microphase separation of compatibilizers in immiscible polymer blends

Macro- and microphase separation of compatibilizing graft copolymers in melt-mixed polystyrene/polyamide-6 blends was studied by transmission electron microscopy and thermal analysis. Three different graft copolymers with main chains of polystyrene and side chains of poly(ethylene oxide) were used as additives at various concentrations. The polyamide-6 domain sizes decreased with increasing amounts of compatibilizing graft copolymers in the blends up to a saturation concentration, after which no further reduction was noted. Macrophase separation of the graft copolymers into discrete macrodomains 20–200 nm in size occurred at concentrations equal to or slightly lower than the saturation concentration. The macrodomains of the graft copolymers were microphase separated, and the sizes and shapes of the microdomains were found to largely depend on the graft copolymer structure and composition. As a consequence of microphase separation, poly(ethylene oxide) crystallinity was noted in blends with sufficiently high macrophase contents. Observations of a graft copolymer interphase between the polystyrene matrix and the polyamide-6 domains confirmed that the graft copolymer was present at the blend interfaces in some of the compatibilized blends. © 1996 John Wiley & Sons, Inc.     

原位聚合聚乙烯/蒙脱土纳米复合材料的结晶行为

用DSC研究了HDPE与MMT负载的催化剂熔融共混和原位聚合得到的两种纳米复合材料的熔融、 结晶行为和等温结晶动力学.  结果表明, HDPE与熔融共混样品的结晶度、 平衡熔点、 球晶生长速率和结晶能力大体相同; 原位聚合得到的HDPE/MMT纳米复合材料的结晶度和平衡熔点高于纯HDPE; 在相同过冷度条件下熔融结晶速率和结晶能力低于纯HDPE, 而在相同结晶温度Tc下, 熔融结晶速率和结晶能力则高于纯HDPE.  纯HDPE的晶体生长侧向单位面积表面自由能最小, 其次是熔融共混样品, 原位聚合样品最大, 且随ＭＭＴ含量的增加逐渐升高.     

Photooxidative behaviour of polyethylene/polyamide-6 blends

The photochemical behaviour of several polyethylene/polyamide-6 blends was studied under conditions of artificial accelerated weathering. Particular attention was paid to five different compositions ranging from pure polyethylene to pure polyamide with blends of PE/PA-6 of various compositions: 75/25, 50/50 and 25/75 wt/wt%. Analysis by infrared spectroscopy of the chemical modifications caused by photooxidation showed that exposing the polyethylene/polyamide-6 blends to UV-light irradiation led to the formation of oxidation photoproducts in both polymer phases. In agreement with both the mechanical and spectroscopic analyses, the photooxidation rate of the blends was observed to be much higher than that of the homopolymers. The results given in this paper suggest that photooxidation of the PE/PA blends starts in the polyamide phase and that the subsequent photooxidation of the polyethylene phase may be initiated by the radicals coming from the oxidation of PA.     

Ringed spherulites in ternary polymer blends of poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone), poly(styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile), and polymethacrylate

The relationship between ringed spherulite morphology, crystallization regimes/kinetics, and molecular interactions in miscible ternary blends of poly(-caprolactone) (PCL), poly(benzyl methacrylate) (PBzMA), and poly(styrene-co-acrylonitrile) (SAN) was investigated by using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The interactions resulted in the deviation of both experimental and calculated T_gs and formation of the specific morphology of the spherulitic structure. Ring-banded spherulites were observed in the PCL/PBzMA/SAN ternary blends. The width of ring bands changed with the blend ratio and the crystallization temperature. Additionally, both composition and wt% of AN in the SAN copolymer had an apparent effect on the morphology of PCL spherulites. Both the crystallization structure of lamellae and molecular interactions greatly influenced the ring bands of PCL spherulites. Furthermore, by using the Flory–Huggins approximation, the depression of the melting point showed that interactions in the PCL/PBzMA/SAN-17 blend were greater than in the PCL/PBzMA/SAN-25 blend. In the ternary blends, the great molecular interactions between amorphous and crystalline polymer resulted in better homogeneity and a larger band period of the extinction rings in the PCL spherulites.     

聚L-乳酸/聚(天冬氨酸-co-乳酸)共混物的制备及其相容性研究

采用氯仿/乙醇共沸溶液浇铸法制备了混合均匀的聚L-乳酸/聚(天冬氨酸-co-乳酸)共混物(PLLA/PAL)体系.研究了PLLA/PAL共混体系的热性能、结晶行为、形态结构和力学性能,评价了PLLA和PAL之间的相容性.结果表明,PAL对PLLA的结晶行为和热性能产生了较大的影响,共混物的结晶度较低,共混体系中部分PAL会进入PLLA球晶的片晶而导致PLLA球晶结构不完善,熔点降低.PAL的含量小于20%的PLLA/PAL共混物的拉伸强度和断裂延伸率均高于纯PLLA.PLLA和PAL分子链相互缠结,产生的氢键使分子链间存在较强的相互作用,具有较好的相容性.     

SPHERULITIC STRUCTURE AND MORPHOLOGY OF POLY(ETHYLENE SUCCINATE)/POLY(ETHYLENE OXIDE) (PES/PEO) BLENDS WITH ONE-STEP CRYSTALLIZATION

The spherulitic structure and morphology development of poly(ethylene succinate)/poly(ethylene oxide) (PES/PEO) blends with one-step crystallization behavior were observed by means of polarizing optical microscope.It was found that the pure PES spherulite in which the adequate quantity of PEO melt existed in the interlamellar regions,and the blending spherulite formed by both PES and PEO lamellae could form simultaneously.When the two types of spherulites contacted with each other the front of the blendi...     

Poly(ethylene oxide) blends with crosslinking polyester resin

The miscibility of polyethylene oxide (PEO) with oligoester and polyester resin, the morphology of the blends and the kinetics of PEO crystallization in the blends were studied by optical microscopy and differential scanning calorimetry. The blends were found to be miscible with uncured resin at 60°C. After isothermal crystallization of PEO from liquid oligoester or UV cured polyester about 20% of the PEO material is still dissolved in the resin and it is incorporated between lamellae or in the interspherulitic regions. It was observed that the growth rate of PEO spherulites and the degree of crystallinity of PEO in the blends decreases very fast together with a decrease of the PEO content and the progress of the resin crosslinking.     

The equilibrium melting temperature and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) and styrene maleimide (c-PBT/SMI) blends

The equilibrium melting point ( $ T_{\text{m}}^{0} $ ) and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) (c-PBT) and styrene maleimide (SMI) blends prepared by solid dispersion and in situ polymerisation of cyclic butylene terephthalate oligomers (CBT) within SMI were investigated. This c-PBT/SMI blend is a miscible semicrystalline–amorphous blend system. The $ T_{\text{m}}^{0} $ of c-PBT/SMI blends was determined using the Hoffman and Weeks method, while Avrami crystallisation kinetic model have been applied to study their isothermal crystallisation kinetics. It was found that $ T_{\text{m}}^{0} $ decreased with increasing SMI content in the blend compositions. All the crystallisation exotherms were obtained from differential scanning calorimetry under isothermal experimental conditions. The average value of Avrami exponent, n, is in the range of 2.4–2.8 for the primary crystallisation process for c-PBT and its blends, which suggest that heterogeneous nucleation of spherulites occurred and growth of spherulites was between two-dimensional and three-dimensional.     

Melt-crystallization behavior and isothermal crystallization kinetics of crystalline/crystalline blends of poly(ethylene terephthalate)/poly(trimethylene terephthalate)

The melt-crystallization and isothermal melt-crystallization kinetics of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends (PET/PTT) were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. Although PET and PTT in the binary blends are miscible at amorphous state, they will crystallize individually when cooled from the melt. In the DSC measurements, PET component with higher supercooling degree will crystallize first, and then the crystallite of PET will be the nucleating agent for PTT, which induce the crystallization of PTT at higher temperature. On the other hand, in both blends of PET80/PTT20 and PET60/PTT40, the PET component will crystallize at higher temperature with faster crystallization rate due to the dilute effect of PTT. So the commingled minor addition of one component to another helps to improve the crystallization of the blends. For blends of PET20/PTT80 and PET40/PTT60, isothermal crystallization kinetics evaluated in terms of the Avrami equation suggest different crystallization mechanisms occurred. The more PET content in blends, the fast crystallization rate is. The Avrami exponent, n = 3, suggests a three-dimensional growth of the crystals in both blends, which is further demonstrated by the spherulites formed in all blends. The crystalline blends show multiple-melting peaks during heating process.     

Periodic radial growth in ring-banded spherulites of poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blends

The isothermal crystallization process of a PCL/SAN blend (90/10 wt.-%) was investigated by using real time image analysis and hot stage optical microscopy. It was found that the growth rate of ringbanded spherulites in the isothermal crystallization process is not constant. Slow growth occurs in the bright bands, while fast growth is found in the dark bands. The radially unequal growth rate of ring-banded spherulites in PCL/SAN blends may be related to the convex band structure on the surface. This new discovery gives us the idea that rhythmic growth is effective in the growth process of ring-banded spherulites.     

CRYSTALLIZATION AND MECHANICAL PROPERTIES OF BLENDS OF METALLOCENE SHORT CHAIN BRANCHED POLYETHYLENE WITH CONVENTIONAL POLYOLEFINS

Metallocene-catalyzed short chain branched polyethylene (SCBPE) was blended with LDPE, HDPE, PS, EPDM and iPP in the weight proportions of 80 and 20. The crystallization and mechanical properties of these blends were studied by PLM, DSC and DMA. It has been observed in PLM that SCBPE/LDPE, SCBPE/HDPE and SCBPE/EPDM can form band spherulites whose band width and size are both smaller than that of the pure SCBPE. Tiny crystallites are observed in the completely immiscible SCBPE/PS blend. The crystallites in SCBPE/iPP are very small and only irregular spherulites are seen. The crystallization kinetics and mechanical properties of SCBPE are greatly affected by the second polyolefin, but in a different way, depending on the phase behavior and the modulus of the second components. SCBPE may be phase miscible in the melt with HDPE, LDPE and EPDM and co-crystallize together with HDPE or LDPE during cooling. A big change of crystal morphology and crystallization kinetics is seen in SCBPE/iPP blend compared with pure SCBPE and the lowest tanδ is also seen for this system. DMA results show that the tensile modulus of the blends has nothing to do with phase behavior, but only depends on the modulus of the second component.     

液晶聚芳醚酮/含甲基苯侧基聚芳醚酮共混体系的环带球晶

本文通过研究含氯侧基液晶聚芳醚酮/含甲基苯侧基聚芳醚酮共混体系(结晶/非晶)环带球晶的形态演变和发展过程; 利用选择性溶剂刻蚀方法确定共混体系环带球晶的相组成和相结构, 探讨了环带球晶的形成机理.     

Crystallization near glass transition: transition from diffusion-controlled to diffusionless crystal growth studied with seven polymorphs

A remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is activated near the glass transition temperature Tg and continues in the glassy state. This growth mode, termed GC (glass-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid. We have studied the GC mode by growing seven polymorphs from the liquid of ROY, currently the top system for the number of coexisting polymorphs of known structures. Some polymorphs did not show GC growth, while others did, with the latter having higher density and more isotropic molecular packing. The polymorphs not showing GC growth grew as compact spherulites at all temperatures; their growth rates near Tg decreased smoothly with falling temperature. The polymorphs showing GC growth changed growth morphologies with temperature, from faceted single crystals near the melting points, to fiber-like crystals near Tg, and to compact spherulites in the GC mode; in the GC mode, they grew at rates 3-4 orders of magnitude faster with activation energies 2-fold smaller than the polymorphs not showing GC growth. The GC mode had rates and activation energies similar to those of a polymorphic transformation observed near Tg. The GC mode was disrupted by the onset of the liquid's structural relaxation but could persist well above Tg (up to 1.15 Tg) in the form of fast-growing fibers. We consider various explanations for the GC mode and suggest that it is solid-state transformation enabled by local molecular motions native to the glassy state and disrupted by the liquid's structural relaxation (the alpha process).     

Miscibility,crystallization kinetics,and morphology of poly(β‐hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(β‐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 PHB. 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. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1860–1867, 2000     

The use of etching techniques to investigate the morphology of mechanically induced transformations in an aliphatic polyketone

Existing permanganic etching techniques have been adapted for an aliphatic polyketone terpolymer to examine its spherulitic and lamellar morphology by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A spherulitic morphology was observed consisting of irregularly shaped spherulites with an average diameter of 5–7 μm and poorly defined spherulite boundaries. Crystalline lamellae were found to be oriented radially within the spherulites. The morphology associated with mechanically induced transformations in a number of deformation systems has been studied and compared to that arising in other common polymeric systems. Changes in morphology through the neck region of drawn samples revealed the elongation of the spherulites as the morphology is transformed from a spherulitic to a fibrillar structure. In samples tested between 23°C and 120°C, radial flaws were observed within the spherulites prior to and within the neck transformation zone. These radial flaws were not observed for samples tested at higher temperatures. Four-point bend tests were conducted on double notched and pre-cracked aliphatic polyketone samples. Examination of the process zone around the crack at the core of the sample revealed crazes characteristic of semicrystalline polymers subjected to a highly constrained stress state. However, the process zone around the crack at the surface of the sample was found to consist of shear bands, suggesting a less constrained damage regime. High cycle fatigue loading also induced flaws oriented radially within the spherulites. Examination of the region around the failure surface in samples fatigue cycled until failure revealed a process consisting of an array of crazes reminiscent to that found in the four-point bend tests. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3246–3255, 1999     

聚乙烯醇/聚乙烯基吡咯烷酮共混体系的结晶行为

用DSC、WAXD和SAXS研究了聚乙烯醇(PVAl)/聚乙烯基吡咯烷酮(PVP)共混体系的结晶行为.PVAl的结晶度随PVP含量增加而减少,并存在结晶度为零的组成(PVAl)的重量分数约为50％.与纯PVAl相比,共混物的温度区间T_m-T_g减小,表明PVP对PVAl的结晶起抑制作用.共混物中PVAl的结晶速度下降,具体表现为PVAl过冷区随PVP含量增加而扩大,动力学速度常数减小,球晶增长速度下降.纯PVAl和共混体系的等温结晶速率均遵循Avrami方程.退火样品的长周期、片晶厚度和过渡层厚度大于相同组成未退火样品.两者长周期随PVP含量增长加显著增大,片晶厚度增长次之,过渡层厚度变化不大.