Study of cure kinetics of DGEBA with optically active curing agents

Kaolin-filled polypropylene (PP) composites with various kaolin content, processing temperature and shear histories were compounded using a heated two roll-mill. Prior to thermal analysis, the samples were subjected to extrusion process via capillary rheometer. The influences of kaolin content, processing temperature and shear stress on crystallization of all samples, including isothermal and nonisothermal crystallization behaviour were investigated by differential scanning calorimetry (DSC). The results showed that the increasing kaolin content, processing temperature and shear stress have shifted the crystallization exothermic peak to higher temperature and reduced the overall crystallization time.     

Crystallization properties and thermal stability of polypropylene composites filled with wollastonite

The influence of wollastonite (CaSiO₃) content on the crystallization properties and thermal stability of polypropylene (PP) composites was investigated. The results showed that the crystallization temperature, crystallization end temperature and crystallization temperature interval, as well as the degree of crystallinity of the composites, were higher than those of the unfilled PP resin, while the crystallization onset temperature was little changed from that of the unfilled PP resin. The increase of degree of crystallinity for the composites could be attributed to the heterogeneous nucleation of the CaSiO₃ in the PP matrix. The thermal stability increased with increasing filler weight fraction (ϕ_f); the thermal decomposition rate decreased nonlinearly with increasingϕ_f. Finally, the dispersion of the filler particles in the matrix was observed, and the mechanisms of thermal stability and crystallizing behavior were discussed.     

Novel filled polymer composites prepared from in situ polymerization via a colloidal approach: I. Kaolin/Nylon-6 in situ composites

A mineral-filled in situ composite was prepared by a colloidal approach by first suspending kaolin filler particles in aqueous caprolactam, and then polymerizing caprolactam in situ at high pressure and temperature. The purpose of this colloidal in situ polymerization is to improve particle dispersion and to enhance interaction of the filler to the polymer matrix. X-ray diffraction studies of the in situ kaolin/Nylon-6 composites revealed that the x-ray peak corresponding to the α-crystal form of Nylon-6 diminished with increasing kaolin loading, while the γ-crystal structure became more pronounced. The degree of crystallinity of Nylon-6 remained fairly unchanged with the kaolin loading level in the in situ composites. Calorimetric and dynamic mechanical studies exhibited that the glass transition temperature of the resulting composite increased significantly with increase in kaolin concentration, suggesting strong filler-matrix interaction at the kaolin/Nylon-6 interface. Scanning electron microscopic (SEM) results showed uniform filler dispersion in the in situ composites relative to the conventional melt-mixed composites. Modulus and tensile strength of these in situ composites were found to be distinctively higher than that of the conventional melt-mixed kaolin/Nylon-6 composites. However, as typical for composite materials, drawability and fracture toughness decreased with increasing kaolin loading. © 1996 John Wiley & Sons, Inc.     

Nucleating Effect and Dynamic Crystallization of a Poly(propylene)/Talc System

The addition of nucleating agents to semicrystalline polymersis largely used in the processing industry of plastic materials to improve some properties of polymers as well as for economical and technological reasons. In this work, the influence of talc concentration on the nucleation efficiency of poly(propylene) (PP), as well as on the non-isothermal kinetics of the crystallization of that system were determined by differential scanning calorimetry (DSC). The nucleating efficiency was determined by Fillon's method, and the dynamic nucleation by Ozawa's method at cooing rates of 2, 5 and 10°C min^–1. The results show that both the degree of crystallinity and the crystallization temperature increase with the filler content and decrease at higher cooling rates and that Ozawa's (n,) exponent and the nucleation efficiency increase with temperature and filler content. It was also shown that the nucleating efficiency of talc in poly(propylene) is comparable to the best heterogeneous nucleating agents available. This revised version was published online in August 2006 with corrections to the Cover Date.     

Static and shear induced crystallization of glass fiber reinforced poly(m‐xylylene adipamide) with nucleating additives

Static and shear induced crystallization studies were carried out on a glass fiber reinforced poly(m‐xylylene adipamide) with various fiber contents. The crystallization experiments were performed using calorimetry and a shearing hot stage coupled with an optical microscope. The crystallization times were measured as a function of the temperature, the shear rate, and the fiber content. In static conditions, no nucleating ability of the fibers was highlighted. However, the shear treatment led to a substantial decrease of the crystallization times for all materials. Moreover, the shear effect is largely influenced by the fiber content, because the shear really undergone by the matrix between the fibers is locally higher than the nominal shear. A previously proposed crystallization kinetics model based on both Avrami and Hoffman–Lauritzen equations and taking into account the nucleating effect of the shear is improved. Hence, the fibers effect is included taking into account the higher local shear between the fibers. The nucleation rate due to the shear is described by a power law of the shear rate, where the prefactor is linked to the fibers amount. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2982–2992, 2007     

Crystallization of poly(ethylene terephthalate) induced by inorganic compounds. I. Crystallization behavior from the glassy state in a low-temperature region

The kinetics of isothermal crystallization from the glassy state at low temperatures and the morphology of poly(ethylene terephthalate) (PET) filled with additives are reported. Talc, kaolin, silicon oxide, and titanium oxide have been used as fillers; they act as effective nucleating agents for PET. The overall rate of crystallization depends on the volume concentration, the size distribution, and the nucleating ability of the additives. An electron microscopic study reveals a transcrystalline morphology at the surface of the filler particles. The occurrence of transcrystallinity is attributed to extensive heterogeneous nucleation induced at the filler surface. From the shape of the crystallization isotherms, it can be concluded that the crystallization mechanism depends on the type of filler.     

Isothermal crystallization kinetics,morphology, and thermal conductivity of graphene nanoplatelets/polyphenylene sulfide composites

Graphene nanoplatelets (GNP) and polyphenylene sulfide (PPS) were used as filler and matrix, respectively, to produce composites. The PPS/GNP thermal composites were prepared via a melt blending method. The effects of GNP on crystallization behavior and kinetics, morphology, and thermal properties of PPS/GNP composites were investigated. To determine the isothermal crystallization kinetics parameters and isothermal crystallization activation energy, the Avrami model was used to comparatively analyze the relevant DSC experimental data. The results show that GNP provides an obvious heterogeneous nucleation effect on PPS to accelerate the crystallization and decrease isothermal crystallization activation energy. Thermal conductivity values of PPS/GNP composites with various GNP contents revealed that GNP remarkably increases thermal conductivity of composites mainly via a layered dispersion in PPS matrix. Thermal conductivity also increased with increasing GNP content, which was further improved at elevated temperatures. The thermal conductivities of PPS composite containing 30 mass% of GNP were 1.156 and 1.350 W m^?1 K^?1 at 30 and 110 °C, respectively, indicating an increase of more than 3 times compared with the neat PPS.     

Non-isothermal crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO3

The processability of ultrahigh molecular weight polyethylene (UHMWPE) improved by oligomer-modified calcium carbonate (CaCO₃) was observed in our previous work. In order to understand the effect of oligomer-modified CaCO₃ on the crystallization of UHMWPE, the non-isothermal crystallization behavior and crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO₃ was studied by differential scanning calorimetry in this work. Jeziorny and Mo methods were used to describe the non-isothermal crystallization kinetics of UHMWPE composites. The effect of modified filler content and cooling rate on the crystallization temperature and crystallization rate was discussed. The heterogeneous nucleation of modified CaCO₃ slightly increases the crystallization temperature of UHMWPE. The crystallization enthalpy of UHMWPE composites is significantly higher than that of UHMWPE. The crystallization rate of UHMWPE composites depends on the filler contents and cooling rate.

     

Transcrystallization of PTFE fiber/PP composites—III. Effect of fiber pulling on the crystallization kinetics

The effect of shear rates on the transcrystallization of polypropylene (PP) on the polytetrafluoroethylene (PTFE) fibers has been quantitatively investigated using a polarized optical microscope equipped with a hot stage and a tensile testing machine. The PTFE fibers were pulled at different rates, from 0.17 to 8.33 μm/s, to induce a range of shear rates, about 0.02 to 1.16 1/s, in the PP melt adjacent to the fiber. The induction time, nucleation rate, and saturated nucleation density at the fiber surface were determined at various crystallization temperatures. It was found that both the nucleation rate and the saturated nucleation density increase with increasing shear rates. However, the induction time is significantly reduced. Based on the theory of heterogeneous nucleation, the interfacial free energy difference functions Δσ;_TCL of PP on PTFE fibers at different levels of shear rates were determined and compared with that obtained from crystallization under quiescent conditions. Results showed that the magnitude of Δσ_TCL decreased to be about one-third of that for the quiescent crystallization, when a shear rate of 1.16 1/s was applied. The application of a shear stress to the supercooled PP melt by fiber pulling leads to enhance the development of transcrystallinity. Moreover, both the thickness and the crystal growth rate of transcrystalline layers were found to increase with the increasing rate of fiber pulling, especially at low crystallization temperatures where regime III prevails (see text). Surface morphology of PTFE fibers was revealed using a scanning electron microscope and an atomic force microscope. It is argued that the presence of fibrillar-type features at the fiber surface is the main factor responsible for the development of transcrystallinity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1361–1370, 1998     

A novel polypropylene composite filled by kaolin particles with β-nucleation

Kaolin-filled polypropylene (PP) composites generally form α-crystal due to the effect of kaolin with α-nucleation. The transition from α- to β-nucleation of kaolin has been investigated, and a novel kaolin with β-nucleation (β-kaolin) and kaolin-filled PP composites with high β-crystal content were prepared first. The DSC and WAXD results indicated that the β-kaolin exhibits stronger β-nucleating ability than CaPA as β-nucleating agent for PP crystallization. It is found that the β-crystal content has been influenced little by filler contents in β-kaolin-filled PP composites. Mechanical properties and spherulitic morphology of filled PP composites was characterized. The synergistic effect of filler and β-crystal significantly improved impact strength of kaolin-filled PP composites.

     

Thermogravimetry as a Method for Investigating the Thermal Stability of Polymer Composites

Thermogravimetry was used to investigate the effects of different inorganic functional fillers on the heat resistance of polymer matrices. The kinetic parameters of thermal oxidative degradation were shown to depend on the polymer, the chemical composition of the filler surface, the filler concentration, and the processing method, which determines the distribution of filler particles in the polymer matrix. Magnetic fillers (carbonyl iron, and hexaferrites of different structural types) were shown to be chemically active fillers, increasing the heat resistance of siliconorganic polymers. Their stabilizing effect is due to blocking of the end silanol groups and macroradicals by the surface of the filler and non-chain inhibition of thermal oxidative degradation. In the case of fiber-forming polymers (UHMWPE, PVOH and PAN), most magnetic fillers are chemically inert, but at concentrations of 30–50 vol% they increase the heat resistance of the composite. Addition of carbon black increased the heat resistance of the thermoplastic matrix. The dependence of the thermal degradation onset temperature on the kaolin concentration in the polyolefin matrix exhibited a maximum. Analysis of the experimental results demonstrated the operating temperature ranges for different composites, and their maximum operating temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of electrical,mechanical, and nanoscale free‐volume properties of NBR and EPDM rubber reinforced by bentonite or kaolin

The effect of Na bentonite, Ca bentonite, and kaolin fillers on the macrostructure and microstructure of acrylonitrile butadiene rubber, ethylene propylene diene rubber, and their blend (50/50) was studied through electrical and mechanical measurements, as well as with positron annihilation lifetime spectroscopy. The real part of permittivity (ε′), dielectric loss (ε″), and the crosslinking density were found to increase with increasing filler content. The increase of crosslinking density of the blend with increasing amount of fillers reflects a decrease in the equilibrium swelling up to 21.50 wt % compared with that of the unfilled blends. The mechanical investigation showed pronounced increase in the tensile strength, and in elongation at break with the addition of up to 21.50 wt % of filler. In addition, comparing between different fillers showed that the reinforcing effect of Na bentonite is more effective than Ca bentonite and kaolin but the physico‐mechanical of Ca bentonite is less than that for kaolin. The positron annihilation lifetime measurements revealed that the free‐volume properties were strongly affected by the amount and type of filler, in particular, the free‐volume fraction was dramatically decreased with increasing filler content. Furthermore, correlations were made between the free‐volume parameters and both electrical and mechanical properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1825–1838, 2009     

EFFECTS OF COUPLING AGENTS ON THE RHEOLOGICAL BEHAVIOR OF KAOLIN FILLED POLYAMIDE 6

An experimental study was carried out to investigate the effects of coupling agents on the rheological properties of kaolin filled polyamide 6(PA6). We have investigated the state of dispersion and interfacial interaction of the filled systems, using 'h:anning electron microscopy (SEM) and Molau test, respectively. It is found that the addition of the coupling agents to the PA6/ kaolin (20 wt percent) significantly decreases the melt viscosity and the melt elasticity (first normal stress difference). Moreover, the states of dispersion and the polymer/filler interactions have significant influences on the rheological properties of kaolin/PA6 systems. The rheological behavior of KH550 kaolin /PA6 system is different from that of KH560 kaolin/PA6 system, although chemical reactions have taken place between the surface of KH550 kaolin (or KH560 kaolin) and PA6 matrix during melt processing. This is attributable, in part, to the differences in the state of dispersion of kaolins in PA6 matrix and, to a great extent, to the differences in the extent of chemical reactions that have taken place between the filler and polymer matrix.     

Surface-esterified cellulose fiber in a polypropylene matrix: impact of esterification on crystallization kinetics and dispersion

Cellulose powders hydrophobized by surface esterification with carboxylic acids with different chain lengths (3, 10 and 18 carbons) were dispersed in a polypropylene matrix. Quality of the dispersion and nucleation activity of the filler were investigated by means of differential scanning calorimetry and optical microscopy. The results showed that the esterification decreases the crystallization rate in case of cellulose esterified with propionic or decanoic acid. On the other hand, the oleic acid ester demonstrated slightly higher crystallization rates than the unmodified cellulose, which was ascribed primarily to the newly arisen non-esterified surface after disintegration of the filler. Optical microscopy with hot stage showed the high nucleation ability of the natural cellulose fiber and its suppression in case of esterified surfaces. A complete inability to nucleate polypropylene crystallization was observed in case of decanoyl ester, while the other two retained some activity, but lower than that of the natural fiber. Finally, analysis of the filler dispersion and distribution revealed that the decanoyl and octadecanoyl esters disintegrate during melt mixing, while both dispersion and distribution of the fibers modified with propionic acid are poor.     

Particle filled polyolefins with high stiffness and toughness,as used for load bearing components

Mineral fillers have been used very often in the past for improving elastic modulus and temperature resistance of polyolefines, also to the detriment of impact resistance. Very recently it has been pointed out that good fracture toughness can be achieved if an appropriate mechanism is stimulated and a good bonding of the filler particles to the matrix is guarantied. This work shows some interesting results obtained in this field with HDPE (high density polyethylene) and kaolin. In particular the effect of filler content and of adhesion between matrix and filler is considered. A comparison is also made with literature data concerning filled polyolefines (HDPE and PP).     

高岭土填充尼龙6的结晶行为

利用差示扫描量热仪（ＤＳＣ）研究了未处理高岭土和经γ－缩水甘油醚氧丙基三甲氧基硅烷（ＫＨ５６０）处理的高岭土对尼龙６等温和非等温结晶行为的影响．结果表明，未处理的高岭土和ＫＨ５６０处理的高岭土在尼龙６基体中都起到异相成核作用．但是，与未处理高岭上相比，ＫＨ５６０处理的高岭土更有效地提高了尼龙６的结晶速率．这一方面归因于ＫＨ５６０处理的高岭土在尼龙６中的分散性好，增大了成核密度；另一方面归因于高岭土经ＫＨ５６０处理后，与尼龙６的相容性增强，从而提高了尼龙６的晶体生长速率．     

热塑性聚氨酯及其复合材料的界面形态与流变特性

以聚酯型热塑性聚氨酯(thermoplastic polyurethane,TPU)、玻璃纤维(glass fiber,GF)和玻璃微珠(glass bead,GB)为主要原料制备了TPU/GF、TPU/GB共混物,考察了复合体系的热性能、微观结构、动态流变特性.研究发现,TPU是温敏型聚合物,其温敏性与材料的硬段含量有关,在加工过程中,除考虑剪切速率的影响外,需重点考虑温度对其加工性能的影响;GF,GB填充TPU体系具有良好的分散形态和界面结合牢度,GF和GB的加入能够增加体系的黏度,降低TPU的温敏性,加宽TPU的加工温度窗口,从而改善其成型加工性,并能一定程度地提高其耐热性.研究还发现,复合体系黏度的增加程度不仅和填料的含量有关,而且与填料的形状有关,可用等效直径表征.另外,从比表面积的角度比较了玻璃纤维和玻璃微珠对体系热稳定性的影响.     

Interfacial interaction in EVA‐carbon nanotube and EVA‐clay nanocomposites

Proper filler‐matrix compatibility is a key factor in view of obtaining nanocomposites with well‐dispersed nanofillers displaying enhanced properties. In this respect, polymer‐filler interaction can be improved by a proper combination of matrix and nanofiller polarities. This is explored for matrices ranging from nonpolar high density poly(ethylene) to ethylene‐vinyl acetate (EVA) copolymers with varying vinyl acetate contents, in combination with several types of organoclay or carbon nanotubes. A novel in situ characterization methodology using modulated temperature differential scanning calorimetry is presented to evaluate the matrix‐filler interaction. During quasi‐isothermal crystallization of the matrix, an “excess” contribution is observed in the recorded heat capacity signal because of reversible melting and crystallization. Its magnitude considerably decreases upon addition of nanofiller in case of strong interfacial interaction, whereas the influence is moderate in case of a less interacting matrix‐filler combination. It is suggested that the “excess heat capacity” can be used to quantify the segmental mobility of polymer chains in the vicinity of the nanofiller. Hence it provides valuable information on the strength of interaction, governed by the physical and chemical nature of matrix and filler. Heating experiments subsequent to quasi‐isothermal crystallization point at a certain degree of molecular ordering, responsible for crystal nucleation in EVA copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1291–1302, 2007     

Development and thermo‐mechanical behavior of nanocomposite epoxy adhesives

Two kinds of organo‐modified (OM) clays were dispersed in an epoxy resin for the preparation of nanocomposite adhesives at various filler amounts. XRD tests evidenced the formation of intercalated structures, increasing the intercalation degree with the clay hydrophilicity. The original transparency of the samples was retained up to a filler content of 3 wt%, and then decreased due to filler agglomeration. The glass transition temperature of nanocomposites filled with the more hydrophilic clay (30B) raised up to a filler content of 3 wt% and then decreased, probably because of the concurrent and contrasting effects of the physical chain blocking and reduction of the cross‐linking degree. Also elastic modulus, stress at break, and fracture toughness were sensibly improved by nanoclay addition up to filler loadings of 0.5–1 wt%. For higher concentrations the positive contribution of clay nanoplatelets was counterbalanced by the presence of agglomerated tactoids in the matrix. Mechanical tests on single‐lap composite (epoxy/glass) bonded joints evidenced an enhancement of the shear strength by about 25% for an optimal filler content of 1 wt%. Therefore, it was concluded that the addition of a proper amount of OM clay to epoxy adhesives could represent an effective way to improve the shear resistance of adhesively bonded composite structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Isothermal crystallization kinetics of PP in PP/Mg(OH)2 composites

The crystallization and melting behavior of PP/Mg(OH)₂ composites was investigated, and the crystallization kinetic parameters and thermal characteristics were investigated according to the Avrami method. Optical polarizing microscope (POM) analysis suggested that the presence of Mg(OH)₂ particles gave rise to an increase in the number of nuclei and a decrease in PP spherulitic size. The Avrami exponent n of the PP and composites increased with increasing crystallization temperature, and markedly deceased with the addition of low Mg(OH)₂ content. A significant increase in crystallization kinetic constant, and a decrease in crystallization half time of PP were observed in the presence of Mg(OH)₂ particles, indicating a heterogeneous nucleating effect of Mg(OH)₂ upon crystallization of PP. The melting temperature and equilibrium melting temperature of PP in the composites decreased with increasing the Mg(OH)₂ content, which is directly related to the size of the PP crystals. The difference of PP melting enthalpies in the PP and composites demonstrated that the presence of Mg(OH)₂ can effectively enhance the crystalline of PP. The crystallization thermodynamics of PP and composites were studied according to the Hoffman theory. Surface free energy of PP chain folding for crystallization of PP/Mg(OH)₂ composites was lower than that of PP, confirming the heterogeneous nucleation effect of Mg(OH)₂. However, the evaluation of the nucleation activation energy of PP suggested the presence of a large amount of Mg(OH)₂ particles in the PP matrix reduced the mobility of PP segments and restricted the development of PP nucleation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1914–1923, 2005