PP/EPDM热塑性弹性体结晶与熔融行为研究

采用动态光交联法制备了PP／EPDM[聚丙烯／（乙烯／丙烯／二烯）共聚物]热塑性弹性体。运用广角X射线衍射（WAXD），偏光显微镜（POM）与差示扫描量热仪（DSC）对PP的结晶形态及结晶与熔融行为进行表征。结果表明，EPDM的加入妨碍PP形成完善的球晶，而动态光交联体系中PP的球晶更不完善；动态光交联对PP的结晶温度及熔点影响不大，结晶度低于未交联体系的。     

Development of Crystalline Morphology,Structure, and Impact Property of Isotactic Polypropylene and Poly(cis-Butadiene) Rubber Blends During Mixing

The development of crystalline morphology, structure, and impact property of isotactic polypropylene (PP) and poly(cis-butadiene) rubber (PcBR) (vol. %: 80/20) blends during mixing were investigated and compared to neat PP. It was found by polarized optical microscopy (POM) and small-angle light scatter (SALS) that the incorporation of PcBR into PP caused small and imperfect PP spherulites and more diffused spherulite boundaries, which sharply exhibited in the initial 2 min of mixing but remained almost unchanged in the rest of the mixing time. Crystalline structure of neat PP and blends was studied by wide-angle x-ray diffraction (WAXD). The addition of PcBR into PP induced formation of PP β-form spherulites. As mixing time developed, the relative degree of crystallization decreased whereas interplanar distance increased. Impact strength of PP and blends was tested. The result showed that impact strength of blends significantly improved with increase of the mixing time.     

Melting and crystallization behavior of poly(trimethylene 2,6-naphthalate)

The melting and crystallization behavior of poly(trimethylene 2,6-naphthalate) (PTN) are investigated by using the conventional DSC, the temperature-modulated DSC (TMDSC), wide angle X-ray diffraction (WAXD) and polarized light microscopy. It is observed that PTN has two polymorphs (α- and β-form) depending upon the crystallization temperature. The α-form crystals develop at the crystallization temperature below 140 °C while β-form crystals develop above 160 °C. Both α- and β-form crystals coexist in the samples crystallized isothermally at the temperature between 140 and 160 °C. When complex multiple melting peaks of PTN are analyzed using the conventional DSC, TMDSC and WAXD, it is found that those arise from the combined mechanism of the existence of different crystal structures, the dual lamellar population, and melting-recrystallization-remelting. The equilibrium melting temperatures of PTN α- and β-form crystals determined by the Hoffman-Weeks method are 197 and 223 °C, respectively. When the spherulitic growth kinetics is analyzed using the Lauritzen-Hoffmann theory of secondary crystallization, the transition temperature of melt crystallization between regime II and III for the β-form crystals is observed at 178 °C. Another transition is observed at 154 °C, where the crystal transformation from α- to β-form occurs.     

Structure formation in stretched sheets of poly(butylene terephthalate)

Crystalline and amorphous sheets of poly(butylene terephthalate) (PBT) were drawn in the temperature range of 20–150°C. The molecular orientation and the relative amount of α- and β-form crystals in the stretched sheets were studied by wide-angle X-ray diffraction (WAXD) and density measurements. When crystalline PBT sheets are drawn at lower temperatures, α-form crystals are partially transformed into β-form crystals. Both α- and β-form crystals are formed by drawing amorphous PBT sheets. The relative amount of α- and β-form crystals is much more sensitive to drawing temperature than to draw ratio. The α-form crystallinity is higher at higher drawing temperature and increases slightly with increasing draw ratio. The second moments of orientation functions of α- and β-form crystals increase with increasing draw ratio, and the increase of the orientation function is suppressed at higher draw ratio. The orientation function of α-form crystals is higher than that of β-form crystals in a same sample.     

Crystallization and orientation behaviors in isotactic polystyrene and poly(2,6-dimethylphenylene oxide) blends

The crystallization and orientation behavior in the miscible iPS/PPO blends were studied aiming at producing oriented materials consisting of iPS crystals and amorphous PPO chains. Oriented films of iPS/PPO blends were prepared by drawing the melt-quenched blend films. The films were heat-treated under constraint at the drawing temperature so as to crystallize the molecular chains of iPS in the oriented state. The crystallinity and the crystal orientation in the drawn annealed films were studied by the wide-angle X-ray diffraction (WAXD), and the orientation behaviors of molecular chains were analyzed by polarized FTIR spectroscopy. WAXD diagrams show the presence of the highly oriented crystalline structure of iPS in the drawn annealed films of pure iPS and iPS/PPO=7/3 blend. The polarized FTIR spectra of drawn annealed films suggest that the molecular orientation of the amorphous chains of PPO and iPS is markedly relaxed by the heat treatment, although the orientation of iPS with 3₁ helical structure was retained during the oriented crystallization. It was concluded that the drawn annealed samples of the iPS/PPO=7/3 blend consist of highly oriented iPS crystals and nearly isotropic amorphous materials. The mechanical properties of the oriented iPS/PPO blends were measured not only in the stretching direction but also perpendicular to the stretching direction. It was shown that the ultimate strength in the perpendicular direction is 4-5 times higher in the drawn annealed film of iPS/PPO=7/3 blend than in the drawn annealed iPS. The improvement in the vertical strength in the blend is discussed in relation to the structural characteristics of the iPS/PPO blend.     

Morphology and nonisothermal crystallization behavior of PP/Novolac blends

The morphology and nonisothermal crystallization behavior of PP/Novolac blends were studied with scanning electron microscopy, differential scanning calorimeter, polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). The results showed that the crystallization of PP in PP/Novolac blends was strongly influenced by cooling rate, size of Novolac particles, crosslinking, and compatibilizer maleic anhydride‐grafted PP (MPP). In dynamically cured PP/MPP/Novolac blends, the MPP grafted on the surface of cured Novolac particles and formed a chemical linkage through the reaction of anhydride groups with the hexamethylenetetramine. The graft copolymer not only improved interfacial compatibility but also acted as an effective heterogeneous nucleating agent, which accelerates the crystallization of PP. The combination of Avrami and Ozawa equations exhibited great advantages in treating the nonisothermal crystallization kinetics in dynamically cured PP/MPP/Novolac blends. The POM results showed that the spherulite morphology and the size of PP in PP/MPP/Novolac blends were greatly affected by Novolac. WAXD experiment demonstrates that the PP and dynamically cured PP/MPP/Novolac blends showed only the α crystal form. At the same time, the addition of Novolac resin also affects the crystal size of PP. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Morphology and thermal properties in the binary blends of poly(propylene-co-ethylene) copolymer and isotactic polypropylene with polyethylene

The morphology and thermal properties of isothermal crystallized binary blends of poly(propylene-co-ethylene) copolymer (PP-co-PE) and isotactic polypropylene (iPP) with low molecular weight polyethylene (PE) were studied with differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). In PP-co-PE/PE binary blends, however, the connected PE acted as a phase separating agent to promote phase separation for PP-co-PE/PE binary blends during crystallization. Therefore, the thermal properties of PP-co-PE/PE presented double melting peaks of PE and a single melting temperature of PP during melting trace; on the other hand, at cooling trace, the connected PE promoted crystallization rate because of enhanced segmental mobility of PP-co-PE during crystallization. At isothermal crystallization temperature between the melting points of iPP and PE, the binary blend was a crystalline/amorphous system resulting in persistent remarkable molten PE separated domains in the broken iPP spherulite. And then, when temperature was quenched to room temperature, the melted PE separated domains were crystallized that presented a crystalline/crystalline system and formed the intra-spherulite segregation morphology: these PE separated domains/droplet crystals contained mixed diluent PE with connected PE components. On the other hand, in the iPP/PE binary blends, the thermal properties showed only single melting peaks for both PE and iPP. Moreover, the glass transition temperature of iPP shifted to lower temperature with increasing PE content, implying that the diluent PE molecules were miscible with iPP to form two interfibrillar segregation morphologies: iPP-rich and PE-rich spherulites. In this work, therefore, we considered that the connected PE in PP-co-PE functioned as an effective phase separating agent for PP and diluent PE may be due to the miscibility between connected PE and diluent PE larger than that between PP and dispersed PE.     

Influence of fractionated crystallization on the semicrystalline structure of (POM/(PS/PPE)) blends. Static and time-resolved SAXS, WAXD and DSC studies

The semicrystalline structure and degree of crystallinity of fractionated crystallizing poly(methylene oxide)/(polystyrene/poly(2,6-dimethyl-1,4 phenylene ether) POM/(PS/PPE) blends have been investigated by DSC, SAXS and WAXD. The three techniques yielded highly correlated results.The degree of crystallinity of the POM phase determined by DSC (X_c,DSC) decreases with decreasing POM content in the blends and this is accompanied by a shift from bulk to homogeneous crystallization.The reduction in the measured degree of crystallinity determined by WAXD (X_c,WAXD) is even more pronounced and indicates, in absence of evidence for the formation of different polymorphs, that only small and imperfect crystals are formed during homogeneous crystallization in finely dispersed droplets. Analysis of the width of the WAXD reflections, which is also related to X_c,WAXD, yields a linear correlation between L₁, a measure of the lateral dimensions of the crystallites, and the average dispersed particle diameter. The parameter L₂, corresponding to the crystalline lamellar thickness, is non-linearly correlated with the degree of crystallinity, indicating that the decrease in X_c,WAXD is not solely due to the formation of thinner lamellae at higher degrees of undercooling. There is a simple relationship between the SAXS long period and the crystallization temperature, corresponding to the formation of thinner and less perfect crystalline lamellae during fractionated crystallization at higher degrees of undercooling.As the lateral dimensions of the crystallites of finely dispersed crystallizing droplets is governed by their size, X_c,WAXD can be directly related to the particle diameter, since the fraction of small or imperfect crystallites will not be measured by WAXD.     

Higher order structures and mechanical properties of bacterial homo poly(3-hydroxybutyrate) fibers prepared by cold-drawing and annealing processes

Pure bacterial homo poly(3-hydroxybutyrate) (PHB) fibers were prepared by melt spinning, followed by cold-drawing in an amorphous state at a temperature just above its glass transition temperature. Cold drawn fibers obtained were further drawn at higher temperatures, followed by annealing at various temperatures under tension. Relations among the processing conditions, higher order structures and mechanical properties were investigated using wide- and small-angle X-ray diffractions (WAXD and SAXD, respectively), birefringence, differential scanning calorimetry (DSC), and tensile measurements. PHB has two different crystalline forms, 2₁ helix conformation (α-form) and planar zigzag conformation (β-form). A single broad reflection of β-form was detected even in a PHB fiber drawn once at a temperature just above its T_g immediately after quenching and it tended to be stronger after 2nd drawing at higher temperatures. Annealing under low temperature and high tension facilitates the occurrence of β-form. It is suggested that the β-form crystal is formed not only from the tie chains between α-form lamella, but also from completely free amorphous chains. Changes in the amount of two types of crystals were analyzed using the WAXD integrated intensity. Birefringence of these fibers shows negative and positive values, depending on process conditions. Changes in higher order structure on the mechanical properties are also discussed.     

Preparation and Properties of PB-1/PP Blends

Crystallization behavior, dynamic mechanical properties, mechanical properties and rheological properties of isotactic polybutene-1/polypropylene (PB-1/PP) blends prepared by melt-blending the two components through Brabender extruder were mainly studied via POM, DSC, DMA, capillary rheometer and so on, respectively. The results indicated that after adding PP in PB-1: size of the spherical crystal and degree of crystallization of PB-1 in the blends decreased, its melt temperature and crystallization temperature unchanged; tensile property of the blends was decreased, but impact and flexural properties were improved; change of the melt viscosity of the blends with the shear rate was more sensitive than pure PB-1.     

稀土β晶成核剂改性nano-CaCO_3/PP复合材料的结晶行为

讨论了稀土β晶成核剂(WBGⅡ)对nano-CaCO3/PP复合材料结晶性能的影响,并借助WAXD、DSC及PLM对PP、nano-CaCO3/PP和WBGⅡ/nano-CaCO3/PP复合材料的结晶行为及晶体形态进行了表征。结果表明:加入少量WBGⅡ后,聚丙烯基复合材料的晶型和球晶形态发生明显变化,提高了材料的起始结晶温度和结晶温度,降低了材料的过冷度,半结晶期延长。     

Blends of thermoplastic polyurethane and polypropylene. I. Mechanical and phase behavior

Pure thermoplastic polyurethane (TPU), polypropylene (PP), and TPU/PP blends with different weight ratios prepared in a twin‐screw extruder were investigated by dynamic mechanical analysis (DMA), the universal tester for mechanical investigation, and by wide‐angle X‐ray diffraction (WAXD). The addition of PP above 20 wt % to the TPU stepwise changed the ductility and Young's modulus, i.e., apparently a kind of ductile → brittle transition occurred between TPU/PP 80/20 and TPU/PP 60/40 blends. This fact and the result of analysis of WAXD curves indicated matrix → dispersed phase inversion in this concentration region. TPU melt enabled easier migration of the PP chains and prolonged crystallization of PP matrix during solidification process affecting thus crystallite size, orientation, and crystallinity. In accordance to this fact, DMA results indicated partial miscibility of PP with polyurethane in the TPU/PP blends due to the lack of interfacial interaction and adhesion between the nonpolar crystalline PP and polar TPU phases. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3980–3985, 2007     

Synergistic toughening effects of nucleating agent and ethylene–octene copolymer on polypropylene

The synergistic toughening effect of nucleating agent (NA) and ethylene–octene copolymer (POE) on polypropylene was studied in the present work. Two different nucleating agents, such as α-form nucleating agent 1,3 : 2,4-bis (3,4-dimethylbenzylidene) sorbitol (DMDBS, Millad 3988) and β-form nucleating agent aryl amides compounds (TMB-5), were selected to blend with PP or PP/POE blends, respectively. The results show that PP containing 0.5–0.25 wt % DMDBS or 0.5–0.25 wt % TMB-5 has relatively low impact strength. For PP/POE blends, although the impact strength increases gradually with the increasing of POE content, high content of POE is needed to obtain the available PP toughness. However, once nucleating agent and POE are simultaneously added into PP, PP/POE/NA blends show great improvement of toughness even at low POE content. Furthermore, the synergistic toughening effect of POE/TMB-5 is more apparent than that of POE/DMDBS. SEM results show that whether DMDBS or TMB-5 has no apparent effect on the morphologies of POE in the PP/POE/NA blends. Further investigations using DSC and POM indicate that both DMDBS and TMB-5 induce the apparent enhancement of the crystallization temperature of PP and the sharp decrease of spherulites size of PP in the PP/POE/NA blends. The possible synergistic toughening mechanism is discussed in the work. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Isothermal crystallization of isotactic polypropylene blended with low molecular weight atactic polypropylene. Part I. Thermal properties and morphology development

The thermal properties and morphology development of isotactic polypropylene (iPP) homopolymer and blended with low molecules weigh atactic polypropylene (aPP) at different isothermal crystallization temperature were studied with differential scanning calorimeter and wide-angle X-ray scattering. The results of DSC show that aPP is local miscible with iPP in the amorphous region and presented a phase transition temperature at T_c=120 °C. However, below this transition temperature, imperfect α-form crystal were obtained and leading to two endotherms. While, above this transition temperature, more perfect α- and γ-form crystals were formed which only a single endotherm was observed. In addition, the results of WAXD indicate that the contents of the γ-form of iPP remarkably depend both on the aPP content and isothermal crystallization temperature. Pure iPP crystallized was characterized by the appearance of α- and γ-forms coexisting. Moreover, the highest intensity of second peak, i.e. the (0 0 8) of γ-form coexisting with (0 4 0) of α-form, and crystallinity were obtained for blended with 20% of aPP, the γ-form content almost disappeared for iPP/aPP blended with 50% aPP content. Therefore, detailed analysis of the WAXD patterns indicates that at small amount aPP lead to increasing the crystallinity of iPP blend, at larger amount aPP, while decreases crystallinity of iPP blends with increasing aPP content. On the other hand, the normalized crystallinity of iPP molecules increases with increasing aPP content. These results describe that the diluent aPP molecular promotes growth rate of iPP because the diluent aPP molecular increases the mobility of iPP and reduces the entanglement between iPP molecules during crystallization.     

Crystallization Behavior of the Blends of Isotactic Polypropylene and Ethylene-Propylene Blocky Copolymers

Two ethylene-propylene copolymer fractions (EP90 and EP120) were separated from a polypropylene in-reactor alloy by extraction with n-octane at different temperatures. ¹³C-NMR shows that these two fractions have a blocky structure and WAXD reveals that both ethylene and propylene sequences in these two fractions are crystallizable. However, EP90 has higher propylene content and the average length of propylene sequences is longer. These two fractions were blended with isotactic polypropylene (PP) at various proportions, respectively, and crystallization behavior and morphology of the blends were investigated. It is found that both EP90 and EP120 are partially compatible with PP. The phase-separated domains have a nucleation effect on crystallization of PP, leading to increase in crystallization temperature and crystallinity of PP in the blends. EP90 and EP120 also affect the relative content of β crystals in an irregular way. The number of EP90-rich domains in PP/EP90 blends is larger than that of EP120-rich domains in PP/EP120 blends, but the size of EP90-rich domains is smaller, indicating that EP90 has better compatibility with PP than EP120. Spherulites are formed in all the blends. The data were analyzed with Hoffman-Lauritzen theory of crystallization regime and the free energy of the folding surface (σ_e) was derived. Addition of EP90 and EP120 has little effect on the transition temperature from regime II to regime III. The value of σ_e for the PP/EP90 blends is similar to that of neat PP, but σ_e of the PP/EP120 blends is a little higher than that of neat PP.     

Crystallization of rare earth oxide-filled polypropylene

A study has been made of the crystallization behavior of polypropylene (PP) filled with rare earth oxides under isothermal conditions. These rare earth oxides include lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), and a mixture of rare earth oxides containing 70% Y₂O₃ (Y₂O₃–0.70). A differential scanning calorimeter was used to monitor the energetics of the crystallization process from the melt. During isothermal crystallization, dependence of the relative degree of crystallinity on time was described by the Avrami equation. It has been shown that the addition of any of the three rare earth oxides causes a considerable increase in the overall crystallization rate of PP but does not influence the mechanism of nucleation and growth of the PP crystals. The analysis of kinetic data according to nucleation theories shows that the increase in crystallization rate of PP in the composites is due to the decrease in surface energy of the extremity surfaces. The relative contents of the β-form in the composites are somewhat higher than that in the plain PP. However, the contents of the β-form in the plain PP and the composites are all very low relative to those of the β-form and the influence of the formation of the β-form on the crystallization kinetics can be neglected. © 1993 John Wiley & Sons, Inc.     

Thermal analysis, X-ray and electron diffraction studies on crystalline phase transitions in solvent-treated poly(hexamethylene terephthalate)

The crystal polymorphism, transformation, and morphologies in chloroform solvent-cast poly(hexamethylene terephthalate) (PHT) were examined by using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and temperature in situ transmission electron microscopy (TEM). Solvent-induced crystallization of PHT at room temperature yielded an initial crystal of γ-form, as confirmed by WAXD. Upon DSC scanning, the original γ-form in PHT exhibited three endothermic peaks, whose origins and association were carefully analyzed. The first peak, much smaller than the other two, is in the temperature range of ca. 100-120 °C. It was found that the solvent-induced γ-form was transformed to β-form at 125 °C via a solid-to-solid transformation mechanism. In addition, WAXD showed that γ- and β-forms co-existed in the temperature range of 100-125 °C. These mixed crystal forms were further identified using TEM, and the selected-area electron diffraction (ED) patterns revealed that both γ- and β-form crystals co-existed and were packed within the same spherulite. Solid-solid transformation from the solvent-induced γ-form to β-form in PHT upon heat scanning was presented with evidence and discussed.     

Crystallization and orientation behaviors of poly(vinylidene fluoride) in the oriented blend with nylon 11

Oriented films of nylon 11/poly(vinylidene fluoride) (PVDF) blend were prepared by uniaxially stretching the melt-mixed blends. The drawn films of fixed length were heat-treated at 170 °C for 5 min to melt the PVDF component, followed by quenching in ice water or isothermal crystallization at various temperatures. The crystal forms and orientation textures of the obtained samples were studied using wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). It was found that PVDF can crystallize into both and β forms in the nylon 11/PVDF blends, and that the content of the β form increases with increasing crystallization temperature above 120 °C. The orientation behavior of the -form PVDF was observed to be dependent on the crystallization conditions: c-axis orientation to the stretching direction was produced for the sample crystallized below 50 °C; the a-axis of crystals was tilted from the stretching direction when PVDF was crystallized at about 75 °C; the parallel orientation of the a-axis to the stretching direction becomes dominant at higher crystallization temperatures (above 100 °C). In contrast, the β crystalline form maintains the c-axis orientation irrespective of crystallization temperature. It was shown by the confocal laser scanning microscopy that cylindrical domains of PVDF were dispersed in the oriented matrix of nylon 11. The mechanism for the formation of the unique orientation textures is discussed in detail. It was proposed that the a-axis orientation is a result of the trans-crystallization of PVDF in the cylindrical domains confined by the oriented matrix of nylon 11. The crystallization kinetics, WAXD analysis, and morphology studies preferred the trans-crystallization mechanism. The mechanical properties of the as-drawn and heat-treated samples were measured not only in the stretching direction but also in the direction perpendicular to it. It was found that the heat-treated samples show slightly lower tensile strength, but more elongation at the break in the two directions than the as-drawn samples.     

Crystallization behavior and morphology of poly(ethylene 2,6-naphthalate)

The crystallization behavior and morphology of poly(ethylene 2,6-naphthalte) (PEN) were investigated by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and transmission electron microscopy (TEM). POM results revealed that PEN crystallized at 240 °C shows the coexistence of α and β-form spherulite morphology with different growth rates. In particular, when PEN crystallized at 250 °C, the morphology of spherulites showed a squeezed peanut shape. The Avrami exponents decreased from 3 to 2.8 above the crystallization temperature of 220 °C, indicating a decrease in growth dimension. Analysis from the secondary nucleation theory suggests that PEN crystallized at 240 °C has crystals with both regime I and regime II. In TEM observation, the ultra-thin PEN film crystallized at 200 °C showed the spherulitic texture with characteristic diffractions of α-form, while PEN crystallized at 240 °C generated an axialite structure with only β-form diffraction patterns. In addition, despite a long crystallization time of 24 h, amorphous regions were also observed in the same specimen. It was inferred that the initiation of PEN at 240 °C generates only β-form crystals from axialite structures.     

乙烯含量对无规共聚聚丙烯晶型及性能影响的研究

通过差示扫描量热分析、X射线衍射分析以及力学性能测试等方法,研究了不同乙烯含量的无规共聚聚丙烯（PPR）体系中,在添加定量β成核剂的条件下,乙烯含量对PPR结晶行为及热学、力学性能的影响。结果表明,PPR的熔点和结晶温度都随其乙烯含量的减少而升高;乙烯含量较少的体系,有利于β晶的形成;体系中β晶含量的提高,会使样品热变形温度提高,且冲击性能显著增强;乙烯含量的提高,增大了PPR β结晶的调控难度;实验室自制β成核剂,可使乙烯含量为0.25 %~5.1 %（质量分数,下同）的PPR中的β晶含量达到80 %以上。