Preparation and nonisothermal crystallization behavior of polypropylene/layered double hydroxide nanocomposites

Polypropylene (PP)/layered double hydroxide (LDH) nanocomposites were prepared via melt intercalation using dodecyl sulfate anion modified LDH and maleated PP as compatibilizing agent. Evidently the interlayer anions in LDH galleries react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual LDH layers in the PP matrix. The nanostructure was characterized by XRD and TEM; the examinations confirmed the nanocomposite formation with exfoliated/intercalated layered double hydroxides well distributed in the PP matrix. The nonisothermal crystallization behavior of resulting nanocomposites was extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. In nonisothermal crystallization kinetics, the Ozawa approach failed to describe the crystallization behavior of nanocomposites, whereas the Avrami analysis and Jeziorny method well define the crystallization behavior of PP/LDH nanocomposite. Combined Avrami and Ozawa analysis (Liu model) also found useful. The results revealed that very small amounts of LDH (1%) could accelerate the crystallization process relative to the pure PP and increase in the crystallization rates was attributed to the nucleating effect of the nanoparticles. Polarized optical microscopy (POM) observations also support the DSC results. The effective crystallization activation energy was estimated as a function of the relative degree of crystallinity using the isoconversional analysis. Overall, results indicated that the LDH particles in nanometer size might act as nucleating agent and distinctly change the type of nucleation, growth and geometry of PP crystals.     

Effect of in situ prepared silica nano-particles on non-isothermal crystallization of polypropylene

The crystallization behavior of PP/silica nanocomposites prepared in-situ via solid-state modification and sol-gel reaction is investigated. The crystallization behavior studied with DSC shows that in situ formed silica nano-particles act as nucleating agents. The non-isothermal crystallization kinetics of PP/silica nanocomposites is studied using a combined Avrami-Ozawa approach and shows a two-stage crystallization process: the primary stage is characterized by nucleation and spherulitic growth and the secondary stage is characteristic of the perfectioning of crystals. Silica speeds up the primary stage, resulting in a more narrow lamellar thickness distribution. The crystallization activation energy decreases with increasing silica content in the PP/silica nanocomposites. The nucleating efficiency of the in-situ prepared silica particles based on the scale as proposed by Lotz and co-workers is found to be 20% in the low concentration range and is higher compared to silica nano-particles as well as other nano-fillers studied. The melting behavior indicates the formation of more perfect crystals with a narrow lamellar thickness distribution and the WAXD patterns show that silica nano-particles induce the formation of crystals with the β-modification in PP at high silica content (ca. 5 wt%). DMTA analysis shows a marginal lowering of the T_g and an increased mobility of the amorphous phase.     

Crystallization kinetics study of dynamically vulcanized PA6/NBR/HNTs nanocomposites by nonisothermal differential scanning calorimetry

Investigation of crystallization behavior and kinetics of thermoplastic elastomer nanocomposites was the subject of limited works because of complexities associated with semiexperimental modeling of such phenomenon in a system containing components having completely different behavior in the molten state. Nonisothermal crystallization kinetics of dynamically vulcanized PA6/NBR/HNTs thermoplastic elastomer nanocomposites was mathematically modeled applying well‐known Avrami, Ozawa, and Mo theoretical models to the differential scanning calorimetry data gathered at various cooling rates. It was found that HNTs contribute as nucleating agents to the crystallization kinetics and cause acceleration of crystallization. Activation energy of the crystallization was calculated by correlating the crystallization peak temperature with the cooling rate using Kissinger model. It was found that Mo equation could properly describe nonisothermal crystallization kinetics of the PA6/NBR/HNTs thermoplastic elastomer nanocomposites. This was recognized from the obtained parameters of Mo equation in terms of HNTs loading level, which suggested a higher rate for dynamic crystallization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46488.     

Structure and properties of polypropylene/clay nanocomposites compatibilized by solid‐phase grafted polypropylene

Polypropylene/organic‐montmorillonite (PP/OMMT) nanocomposites were prepared via a solid‐phase PP graft (TMPP) with a higher grafting level as the compatibilizer. The effects of the compatibilizer on the structure and properties of PP/OMMT nanocomposites were investigated. The structure of the nanocomposites were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that when the weight ratio of TMPP and OMMT is greater than 1:1, the OMMT can be dispersed in PP matrix uniformly at the nanoscale. The mechanical properties of the nanocomposites reached a maximum when the weight ratio of TMPP and OMMT is 1:1, although more uniform dispersion was achieved at a higher content of TMPP. The mechanical properties of the nanocomposites decrease with the content of TMPP. The crystallization behavior, dynamic rheological property, and thermal stability of the nanocomposites were investigated by differential scanning calorimetry (DSC), dynamic rheological analysis, and thermal gravimetric analysis (TGA), respectively. Due to the synergistic effects of TMPP and OMMT on the crystallization of PP, the crystallization peak temperature of the nanocomposites increased remarkably compared with that of the neat PP. TMPP shows β‐phase nucleating ability and OMMT promotes the development of β‐phase crystallite. The nanocomposites show restricted melt flow and enhanced temperature sensitivity compared with the neat PP. The thermal stability of the nanocomposites is obviously improved compared with that of the neat PP. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers.     

Water-assisted extrusion as a novel processing route to prepare polypropylene/halloysite nanotube nanocomposites: Structure and properties

Naturally occurring halloysite nanotubes (HNTs) are used to prepare Polypropylene (PP)/HNTs nanocomposites using a novel “one step” water-assisted extrusion process with and without the use of a PP-graft-maleic anhydride (PP-g-MA) as compatibilizer. In order to analyze the influence of PP-g-MA and/or water injection on the HNTs dispersion and therefore on nanocomposite properties, structural analysis (SEM and TEM) is combined with rheological and thermo-mechanical experiments. The best clay dispersion is obtained when compatibilizer and water injection are combined together (synergistic effect). As a consequence, the linear viscoelastic properties and the dynamic storage modulus are dramatically enhanced for this system. A mechanism explaining the interaction between HNTs and PP-g-MA in presence of water is proposed. The thermal stability and flame retardant property are also investigated. Thermal analyses reveal two opposite effects of HNTs on the thermal behaviour of PP. A surface catalytic action of the halloysite speeds up thermal degradation of PP. However, this effect is reduced with improved HNTs dispersion, presumably via an entrapment mechanism of the decomposition products inside the lumens. Finally, cone calorimeter results show that low flammability of nanocomposites is only achieved when combining water injection and PP-g-MA. In view of these results, PP/HNTs nanocomposites prepared using this novel processing route are promising candidates for flame retardant applications.     

Morphology,Rheological Properties,and Crystallization Behavior of Polypropylene/Clay Nanocomposites

Polypropylene/clay nanocomposites (PP/I.44P, PPCNs) were prepared in a twin-screw extruder using maleic anhydride grafted polypropylene (MAPP) as a compatibilizer. The intercalation of polypropylene into nanoclay particles was studied using X-ray diffraction. Rheological properties of the nanocomposites were investigated using a rheometer. The enhanced complex viscosity at low frequency regime indicated that the melt elasticity and melt strength of the nanocomposites were improved by adding nanoclay. The non-isothermal crystallization behavior of the nanocomposites was studied using differential scanning calorimetry (DSC) at various cooling rates and was analyzed with the Avrami method. It was found that the nanoclay acted as a heterogeneous nucleating agent resulted in higher crystallization temperature and higher crystallization rate than neat PP. Polarized optical microscopy revealed that the spherulites in the nanocomposites were finer than in the neat system.     

Crystallization behavior and mechanical properties of polypropylene/halloysite composites

In this work, halloysite nanotubes (HNTs), a new type of inexpensive filler, were used for the modification of polypropylene (PP). HNTs were first surface treated by methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium, then melt mixed with PP. Scanning electron microscope (SEM) was used to examine the dispersion of HNTs in PP matrix. Differential scanning calorimetry (DSC), polarized light microscope (PLM), dynamic melt rheometry and wide angle X-ray diffraction (WAXD) were employed to investigate the crystallization behavior of the prepared PP/HNT composites. The mechanical properties were evaluated by Instron and impact tests. SEM results revealed that HNTs could be well-dispersed in PP matrix and had a good interfacial interaction with PP, even up to a high content of 10 wt%. DSC data indicated that HNTs could serve as a nucleation agent, resulting in an enhancement of the overall crystallization rate and the non-isothermal crystallization temperature of PP. PLM showed a constant spherulite growth rate and a decreased spherulite size at given isothermal crystallization temperature, suggesting that nucleation and growth of a spherulite are two independent processes. The result obtained by dynamic melt rheometry indicated that HNTs mainly promoted nucleation and had not much influence on the growth of PP crystallization. Nevertheless, by fast cooling the samples, almost constant spherulite size can be obtained for both pure PP and PP/HNT composites due to the limited nucleation effect of HNTs on PP crystallization. WAXD showed that HNTs mainly facilitated α-crystal form of PP. Though a good dispersion of HNTs in PP matrix was observed, out of our expectation, not much enhancement on mechanical properties of PP/HNT composites had been achieved, and this could be mainly ascribed to the constant crystallinity and spherulite size of PP as well as the small length/diameter ratio of HNTs.     

Development of waste tire‐derived graphene reinforced polypropylene nanocomposites with controlled polymer grade,crystallization and mechanical characteristics via melt‐mixing

In the present work, single layer graphene nanoplatelets (GNPs) derived from waste tires by recycling and upcycling approaches were integrated in homopolymer (Homo‐) and copolymer (Copo‐) polypropylene (PP) matrices by fast and efficient mixing in the melt phase. The effect of GNP content on crystallization and mechanical behaviors was investigated in detail at different loading levels. Regarding isothermal and non‐isothermal crystallization experiments, GNPs significantly accelerated the nucleation and growth of crystallites, and the crystallization degree in Homo‐PP nanocomposites was slightly higher than that of Copo‐PP based nanocomposites. Also, there was significant improvement in mechanical and thermal properties of GNP reinforced polymers compared to neat polymers. As the GNP concentration increased from 1 to 5 wt%, there was a gradual increase in flexural modulus and strength values. In tensile tests, an increase in GNP content in both polymer grades led to a slight increase in yield strength coming from the proper distribution of nano‐reinforcement by creating stress concentration sites. After the yield point, Homo‐PP based nanocomposites showed higher strain hardening than GNP reinforced Copo‐PP owing to a high crystallization degree and linear chains of Homo‐PP. This work showed that functionalized graphene can act as both nucleating and reinforcing agent in the compounding process and its exfoliation through polymer chains is much better in homopolymers at a faster and high shear rate. © 2020 Society of Chemical Industry     

Polypropylene-organoclay nanocomposites containing nucleating agents

Polypropylene/organoclay nanocomposites containing nucleating agents, viz., aluminum hydroxybis[2,2-methylenebis(4,6-di-tert-butylphenyl) phosphate (NA21) and 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (Millad 3988), were prepared by direct melt intercalation in a twin-screw extruder. Nucleating agents were added to polypropylene during compounding and their effect on the properties of the nanocomposites was studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) exhibited clay layers to be intercalated and partially exfoliated. The expansion of inter-gallery distance of the clay layers was governed by the interaction between polypropylene, compatibilizer, and different nucleating agents. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated higher thermal stability and crystallization temperature for nanocomposites compared to virgin polymer. Even a small addition of the nanoscale filler with 0.2% nucleating agents was found to promote concurrently several PP material properties, including improved tensile characteristics, higher Young’s modulus, increased thermal stability and rate of crystallization.     

己二酸/无水硫酸钙晶须改性PP的等温结晶动力学

通过差示扫描量热(DSC)仪分析了己二酸(AA)和无水硫酸钙晶须(ACSW)复配改性聚丙烯(PP)的等温结晶行为,用偏光显微镜(PLM)观察了AA/ACSW复配改性PP的晶体形貌。DSC分析结果表明,随着结晶温度升高,半结晶时间和最大结晶时间增加,半结晶速率降低;与纯PP相比,ACSW和AA/ACSW复合改性都能使PP的结晶时间降低,结晶效率增加,说明ACSW和AA/ACSW对PP具有异相成核作用,并且AA/ACSW复合改性PP对提高PP的结晶性能有更好的效果,此外ACSW改性PP的等温结晶活化能最低。对改性PP的PLM的观察说明ACSW对PP具有异相成核作用,而AA/ACSW对PP的β晶成核具有协同促进作用。     

聚丙烯基高含量埃洛石纳米管复合材料的制备和性能

采用双螺杆挤出机制备聚丙烯(PP)基高含量(33 phr)埃洛石纳米管(HNTs)复合材料,从挤出机沿程3个位置和机头出口处取样,观察样品的微观结构并测试其流变性能和热稳定性。结果表明,本文设置的螺杆结构提供的分散和分布混炼使PP/HNTs复合材料中HNTs团聚体的尺寸快速减小,HNTs在PP基体中分散得越来越均匀,使挤出机沿程3个位置所取复合材料样品的低频区储能模量逐渐提高、末端斜率逐渐降低、松弛时间逐渐变长。机头入口所取复合材料样品的热稳定性要比机头出口样品的高,这归因于前者样品中较为无序且较均匀排列的HNTs纳米空腔能更有效地诱捕降解产物。     

Effect of continuous oscillatory shear on isothermal crystallization of non‐nucleated and nucleating‐agent‐treated isotactic polypropylene assessed by dynamic mechanical analysis

Using dynamic mechanical analysis (DMA), we investigated the in situ crystallization kinetics of non‐nucleated and nucleating‐agent‐treated isotactic polypropylene (iPP) under continuous oscillatory shear during the entire crystallization process, and then compared the DMA results with those measured using differential scanning calorimetry under conventional quiescent crystallization. Our analyses, based on the Avrami equation, show that continuous oscillatory shear accelerated crystallization of non‐nucleated iPP, but interfered with crystallization for nucleating‐agent‐treated iPP. Our results indicate that, for the present nucleating agent, its accelerating effect on crystallization cannot coexist with the accelerating effect of shear on crystallization. We attributed this difference to the disruptive effect of shear on growth and the different nucleation models of non‐nucleated and nucleating‐agent‐treated iPP. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41685.     

The effect of crystallization on the structure and morphology of polypropylene/clay nanocomposites

The effect of crystallization on the structure and morphology of maleic anhydride grafted polypropylene (PP‐MA)/clay (montmorillonite) nanocomposites (PPCNs) is presented. Wide‐angle X‐ray diffraction (WAXD) measurements of PPCNs crystallized at different temperatures show that the extent of intercalation increases with the crystallization temperature. The enhancement of intercalation occurs with lower clay content PPCNs, and maximum intercalation takes place for 4 wt% clay content. The mechanism of intercalation has been proposed through crystallization. Excess γ‐form of the crystallite of PP‐MA appears in presence of clay, possibly because of the confinement of the polymer chain between the clay particles. WAXD data also reveals that d‐spacing increases gradually with clay content. The decrease of spherulitic size is observed with increasing clay content, which indicates that clay particles act as nucleating agents. Lamellar textures have been explored by using small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM), which exhibit that both the lamellar thickness and long period of the PPCNs are higher than those of PP‐MA.     

聚丙烯/蒙脱土纳米复合材料的研究进展

介绍了聚丙烯/蒙脱土纳米复合材料的制备原理及插层方法。并对国内外的研究进展进行了综述，讨论了蒙脱土对聚丙烯结晶性能的影响。蒙脱土的加入聚丙烯有异相成核的作用。另外介绍了聚丙烯/蒙脱土纳米复合材料中蒙脱土对聚丙烯力学性能的影响。其力学性能随蒙脱土含量的增加先增加后下降。     

Effect of Nanoparticle Surface Treatment on Nonisothermal Crystallization Behavior of Polypropylene/Calcium Carbonate Nanocomposites

Polypropylene (PP)/CaCO₃ nanocomposites were prepared by melt-blending method using a Haake-90 mixer. The CaCO₃ nanoparticles were surface modified with a coupling agent before compounding. A fine dispersion of the modified nanoparticles in the nanocomposites was observed by transmission electron microscopy (TEM). Effects of surface treatment of CaCO₃ nanoparticles on the nonisothermal crystallization behavior and kinetics of PP/CaCO₃ nanocomposites were investigated by differential scanning calorimetry (DSC). Jeziorny and Mo methods were used to describe the nonisothermal crystallization process. It was shown that the crystallization temperature of the nanocomposites increased due to the heterogeneous nucleation of the surface-treated nanoparticles. It was found that the nanoparticles modified with a proper content range of coupling agent could facilitate the nonisothermal crystallization of the nanocomposites under certain conditions (the cooling rate and the relative degree of crystallinity). This may be a potential application for the crystallization controlling of composites in manufacturing. In addition, the activation energy of crystallization for the nanocomposites and the nucleation activity of the nanoparticle were estimated by using Kissinger and Dobreva's methods, respectively. It could be concluded that the surface-treated nanoparticles had a strong nucleating activity, which caused the decrease of the activation energy of the nanocomposites.     

聚丙烯釜内釜外成核评价

借助于热分析和力学性能测试考察了釜内与釜外添加成核剂对聚丙烯(PP)结晶行为和力学性能的影响。研究结果表明：2种添加方式对PP结晶温度影响不大,而釜内成核方式能更进一步提高结晶速率,成核PP的弯曲模量、低温抗冲击性能和热变形温度显著提高。     

石墨烯/聚丙烯复合材料的等温结晶动力学研究

采用差示扫描量热仪(DSC)研究了石墨烯(RGO)/聚丙烯(PP)复合材料的等温结晶行为。结果表明:对于纯PP和RGO/PP复合材料,结晶温度(Tc)的提高将导致结晶速率(G1/2)变慢、绝对结晶度(Xc)提高;PP和RGO/PP复合材料的等温结晶在相当大的范围内符合Avrami方程;同纯PP相比,RGO/PP复合材料的G1/2相对增加,而结晶活化能相对减小,这意味着RGO对PP起到了外加成核剂的作用,促进了PP的结晶。     

Nonisothermal crystallization behavior and mechanical properties of poly(butylene succinate)/silica nanocomposites

Silica nanoparticles and poly(butylene succinate) (PBS) nanocomposites were prepared by a melt‐blending process. The influence of silica nanoparticles on the nonisothermal crystallization behavior, crystal structure, and mechanical properties of the PBS/silica nanocomposites was investigated. The crystallization peak temperature of the PBS/silica nanocomposites was higher than that of neat PBS at various cooling rates. The half‐time of crystallization decreased with increasing silica loading; this indicated the nucleating role of silica nanoparticles. The nonisothermal crystallization data were analyzed by the Ozawa, Avrami, and Mo methods. The validity of kinetics models on the nonisothermal crystallization process of the PBS/silica nanocomposites is discussed. The approach developed by Mo successfully described the nonisothermal crystallization process of the PBS and its nanocomposites. A study of the nucleation activity revealed that the silica nanoparticles had a good nucleation effect on PBS. The crystallization activation energy calculated by Kissinger's method increased with increasing silica content. The modulus and yield strength were enhanced with the addition of silica nanoparticles into the PBS matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

增韧剂及成核剂对PP–R复合材料性能的影响

采用注射成型法制备无规共聚聚丙烯(PP–R)复合材料,结合差示扫描量热仪、扫描电子显微镜、X射线衍射仪及偏光显微镜等技术,分析了乙烯–辛烯共聚物+高密度聚乙烯增韧剂及WBGⅡ型β成核剂对PP–R复合材料力学性能和结晶行为的影响。结果表明,增韧剂与成核剂对复合材料的综合性能有明显的影响,β成核剂和增韧剂同时加入到PP–R材料中,协效提高了复合材料的冲击强度,为78.7 k J/m~2,与纯PP–R材料比较提高了175%,而对拉伸及弯曲强度影响较小。同时,加入增韧剂及成核剂均能诱导α晶向β晶转变,晶粒细化,进而改善其冲击韧性。     

Fatigue and hysteresis behavior of halloysite nanotubes‐filled natural rubber (SMR L and ENR 50) nanocomposites

The effect of various halloysite nanotubes (HNTs) loading on fatigue life, stress–strain behavior, and hysteresis of HNTs/Standard Malaysian Rubber (SMR) L and HNTs/epoxidized natural rubber (ENR) 50 nanocomposites were studied. The addition of HNTs caused decrement in fatigue life for both nanocomposites at any extension ratio. Generally, HNTs/SMR L nanocomposites showed higher fatigue life than ENR 50 nanocomposites. Addition of more HNTs caused decrement of stress for HNTs/SMR L nanocomposites, whereas HNTs/ENR 50 nanocomposites showed vice versa at any strain. This result was supported by the graph of accumulated strain energy against extension ratio. Hysteresis values increased with addition of HNTs in both nanocomposites where of HNTs/ENR 50 nanocomposites exhibited higher hysteresis than HNTs/SMR L nanocomposites at any HNTs loading. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013