The J-integral fracture toughness of PP/CaCO3 composites

The J-integral method was introduced to investigate the fracture process of PP/CaCO₃ composites. The results showed that the resistance of PP/CaCO₃ composites to crack initiation and propagation was greatly improved with the addition of CaCO₃ filler. Large scale plasticity was caused in PP/CaCO₃ composites, from which a large amount of energy was absorbed by the PP matrix. The reason for the increase in the fracture toughness of PP/CaCO₃ composites was attributed to the partial micro-drawing ahead of the crack tip in the PP matrix, which was formed by the stress concentration caused by the filler particles in the PP matrix and/or by the interfacial debonding between filler particles and the PP matrix. It was indicated that the presence of CaCO₃ filler could augment the ductility of composites locally, resulting in higher fracture energy in the crack initiation and propagation of the PP/CaCO₃ composites in a certain CaCO₃ content range.     

Tensile and fracture behaviour of PP/wood flour composites

Polypropylene/wood flour composites with different fibre content were prepared. The effect of composition and the incorporation of maleinated polypropylene on the materials tensile and fracture and failure behaviour was investigated. Reliable fracture toughness data that will be useful for structural applications were obtained. In unmodified composites an increase in Young´s modulus was found with the addition of wood flour to PP, whereas tensile strength, strain at break and fracture toughness were observed to decrease as fibre content increased. The presence of MAPP was beneficial to tensile strength and ductility and had no significant effect on fracture toughness, as a result of enhanced fibre dispersion within the matrix and improved interfacial adhesion. Although reduced ductility and toughness were observed for the composites respect to the matrix, in the case of modified composites, environmentally friendly stiffer materials were obtained with cost saving without sacrificing strength.     

Effect of morphology on the behaviour of ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO₃ or Mg(OH)₂) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (_y) for the two limiting morphologies over an interval of elastomer volume fractions (V _e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.     

Control of the structure and properties of barium sulphate-filled blends of polypropylene and ethylene propylene copolymers

The structure and properties of polypropylene (PP) and ethylene propylene copolymer (EPR) blends filled with BaSO₄ have been investigated. The aspect of structure control concerned was the separate dispersion of filler and rubber in the PP matrix or encapsulation of the filler in the rubber phase. The former structure prevails in the PP/EPR/BaSO₄ systems, and addition of maleic anhydride-grafted polypropylene (MAPP) enhances the adhesion between the PP matrix and the filler. Encapsulation of the filler particles into the elastomer takes place when maleated EPR-rubber (EPMA) is used, and the encapsulated structure prevails even under the severe shearing conditions of injection molding. The improved matrix/filler adhesion resulted in increased yield stress and tensile strength, but decreased impact resistance. The particle size of the filler proved to be a crucial factor; below a certain particle size aggregation becomes a dominating factor. Extensive aggregation leads to the deterioration of all mechanical properties, especially to decreased impact strength.     

Effect of coupling agents on reinforcing potential of recycled carbon fibre for polypropylene composite

Polypropylene (PP) composites reinforced with recycled carbon fibre have been prepared through extrusion compounding and injection moulding. The reinforcing potential of the recycled fibre was increased by improving the interfacial adhesion between the fibre and PP matrix and this was done by the addition of maleic anhydride grafted polypropylene (MAPP) coupling agents. Three MAPP couplers with different molecular weights and maleic anhydride contents were considered. The effects on the mechanical properties of the composite were studied, and scanning electron microscopy (SEM) was used to study the fracture morphology of the tensile specimens. It was observed that with the addition of MAPP the interfacial adhesion was improved as fewer fibres were pulled-out and less debonding was seen. A microbond test was performed and a significant improvement in interfacial shear strength was measured. This resulted in composites with higher tensile and flexural strengths. The maximum strength was achieved from MAPP with the highest molecular weight. Increased modulus was also achieved with certain grades of MAPP. It was also found that the composite impact strength was improved significantly by MAPP, due to a higher compatibility between the fibre and matrix, which reduced crack initiation and propagation.     

Enhancement of tensile and thermal properties of epoxy nanocomposites through chemical hybridization of carbon nanotubes and alumina

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid carbon nanotube–alumina (CNT–Al₂O₃) filler, via chemical vapour deposition and a physically mixed CNT–Al₂O₃ filler, at various filler loadings (i.e., 1–5%). The tensile and thermal properties of both nanocomposites were investigated at different weight percentages of filler loading. The CNT–Al₂O₃ hybrid epoxy composites showed higher tensile and thermal properties than the CNT–Al₂O₃ physically mixed epoxy composites. This increase was associated with the homogenous dispersion of CNT–Al₂O₃ particle filler; as observed under a field emission scanning electron microscope. It was demonstrated that the CNT–Al₂O₃ hybrid epoxy composites are capable of increasing tensile strength by up to 30%, giving a tensile modulus of 39%, thermal conductivity of 20%, and a glass transition temperature value of 25%, when compared to a neat epoxy composite.     

Structure–fracture properties relationship for Polypropylene reinforced with fly ash with and without maleic anhydride functionalized isotactic Polypropylene as coupling agent

The deformation and fracture behavior of PP/ash composites with and without maleic anhydride functionalized iPP (MAPP) as coupling agent was investigated, focusing on the effect of ash content and loading conditions. A decreasing trend of tensile strength and strain at break values with filler content was observed for unmodified composites, whereas these properties were roughly independent of ash content for the composites with MAPP. In quasi-static fracture tests, all materials displayed ductile behavior. Most composites exhibited improved fracture properties with respect to the matrix as a result of the toughening mechanisms induced by the ash particles. Under impact loading conditions, in contrast, all materials displayed fully brittle behavior. Impact critical fracture energy values of the composites were higher than those of PP and they also presented a maximum which was explained in terms of the comprehensive analysis of the crystallinity development in PP. The incorporation of MAPP led to better dispersion of ash particles in the matrix but was detrimental to the material fracture behavior independently of loading conditions. Increased interfacial adhesion promoted by MAPP hindered particle-induced toughening mechanisms.     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

Isocyanate as a compatibilizing agent on the properties of highly crystalline cellulose/polypropylene composites

Composites of a highly crystalline cellulosic microfibres with polypropylene (PP) as well as with maleic anhydride grafted polypropylene (MAPP) were prepared by using 1,6-diisocyanatohexane (DIC) as a compatibilizing agent, their mechanical properties, morphologies, and thermal properties were investigated. Results show that the tensile strength and young’s modulus of the composites improved intensively by using DIC. The enhancement is proposed to be due to stronger interfacial adhesion caused by the reduction of the polarity and hydrophilicity of cellulose fiber in PP-based composites, while much more chemically bound MAPP chains on cellulose fiber in MAPP-based composites. A maximum on tensile properties of the composite can be obtained by optimizing of the DIC content. Scanning electron microscopy (SEM) indicates that the interfacial adhesion between cellulose fibers and PP or MAPP matrix was improved in DIC coupled composites. Furthermore, DIC yields also some effects on thermal dynamic mechanical properties, as well as melting and crystallization behavior of the composites.     

Physical and mechanical properties of SEBS/polypropylene nanocomposites reinforced by nano CaCO3

In present study, styrene‐b‐(ethylene‐co‐butylenes)‐b‐styrene triblock copolymer (SEBS) and polypropylene (PP) are prepared. This mixing is followed by adding 3, 5 and 10 wt% of nano CaCO₃. The morphology and thermal behavior of PP/SEBS/nano‐CaCO₃ compounds are characterized by different methods. Scanning electron microscopy micrographs of cryo‐fractured PP/SEBS/nano‐CaCO₃ nanocomposites show that with increasing nano‐CaCO₃ loading, the aggregation becomes worse. However, followed by adding 5 wt% nano‐CaCO₃ into PP/SEBS nanocomposites, nano‐CaCO₃ is homogeneously dispersed in PP matrix. The photomicrograph of transmission electron microscopy confirms that SEBS/PP/nano‐CaCO₃ nanocomposites are formed, as low aggregations of calcium carbonate were well‐dispersed in polymer matrix. With a rise in nano‐filler content, the tensile and impact strength of PP/SEBS/CaCO₃ nanocomposite are fixed while the elastic modulus of PP/SEBS nanocomposites increases followed by adding nano‐CaCO₃ to polymer blend, which could be due to the acceptable nano‐CaCO₃ dispersion quality.     

Evaluation and control of the adhesiveness of cohesive calcium carbonate particles at high temperatures

Understanding the adhesiveness of fine particulate materials at high temperatures is important to achieving the stable, economical operation of various industrial systems. In the present research, two types of calcium carbonate (CaCO₃) particles having different mean particle sizes (often used as heat carriers in energy systems) were evaluated. The tensile strengths of beds of these materials were determined at various temperatures by tensile strength measurement tester. The adhesiveness was found to increase greatly at 500 °C even without chemical reactions or sintering, and X-ray diffraction analyses showed thermal expansion of the CaCO₃ crystals at 500 °C. Pure alumina (Al₂O₃) and silica (SiO₂) microparticles did not exhibit the same pronounced increases in tensile strength or crystal expansion at this same temperature. Because the surface distances between these primary particles were presumably small, it is proposed that van der Waals forces between the particles greatly increased at high temperatures. The addition of Al₂O₃ nanoparticles to the CaCO₃ decreased the tensile strengths of the powder beds both at ambient temperature and at 500 °C. The experimental data confirm that the surface distances between primary particles were increased upon incorporating the nanoparticles, such that the tensile strength decreased during heat treatment.     

Polypropylene/SiO<Subscript>2</Subscript> nanocomposites filled with different nanosilicas: thermal and mechanical properties,morphology and interphase characterization

Untreated and surface-treated SiO₂ nanoparticles with different alkyl chain length (described as C0, 3C1, C8 and C16 according to the number of carbon atoms) on particle surface were used as fillers for isotactic polypropylene (iPP). The iPP/SiO₂ composites containing 2.3 vol% of nanoparticles were prepared by melt blending and injection moulding. The dispersion quality of nanoparticles in matrix was examined using scanning electron microscopy (SEM). The crystallization behaviour of iPP was examined using differential scanning calorimetry (DSC). The mechanical properties of all samples were characterized by tensile test, compact tension (CT) test and dynamic mechanical thermal analysis (DMTA). The particle–matrix interphase behaviour was also examined and discussed. SEM images show that different silicas show different dispersion quality in matrix due to different hydrophobicity. The crystallinity and spherulite size of matrix are overall decreased in composites. The tensile properties of iPP/SiO₂ composites show clear relationship with alkyl chain length on particle surface, i.e. increasing alkyl chain length leads to decreased tensile modulus but increased tensile yield strength and strain, indicating increased interfacial interactions with increased alkyl chain length. The 3C1-composite shows the highest fracture toughness with an improvement by 9% compared to neat iPP, whereas the other composites show decreased values of fracture toughness.     

Microstructure and mechanical properties of polypropylene/polystyrene blend filled with as-synthesized MCM-41 prepared by melt-compounding

Nano-sized as-synthesized MCM-41 particle, whose pore channels and outer surface full of organic CTAB template, was used as compatibilizers for immiscible polypropylene (PP)/polystyrene (PS) blends. In this paper, the solid structure SiO₂ was selected to compare with as-synthesized MCM-41 in properties of PP/PS blend. The mechanical results showed that tensile strength of the blend was increased by 32% and the impact strength was increased by 41.1% by addition low content of as-synthesized MCM-41 compared to pure PP/PS. The presence of SiO₂ in the blend cannot improve the mechanical properties obviously. SEM indicated that incorporation of as-synthesized MCM-41 into PP/PS blend can act as compatibilizer, which resulted in a decreased particle size of dispersion phase together with morphological evidence of interfacial adhesion. However, with the presence of SiO₂, 1%, 3%, in the blend, the interface did not show clear change compared with the PP/PS blend.     

Deformation and failure of PP composites reinforced with lignocellulosic fibers: Effect of inherent strength of the particles

PP/wood composites were prepared from two lignocellulosic fibers with different particle size and aspect ratio in order to determine the effect of these factors on the deformation and failure mechanism as well as on the properties of the composites. Wood content was changed from 0 to 80 wt%. Maleinated polypropylene (MAPP) was added to improve interfacial adhesion. The MAPP/wood ratio was kept constant at 0.1. Mechanical properties were determined by tensile testing. Micromechanical deformation processes were followed by acoustic emission (AE) and volume strain (VOLS) measurements, and by the study of fracture surfaces. The results proved that micromechanical deformations change drastically both with decreasing particle size and changing interfacial adhesion. Less debonding, fiber pull out and fiber fracture occur in composites containing small particles. Hardly any change was observed in the mechanical properties of the composites with decreasing particle size, in spite of the drastic modification of the deformation mechanism. The apparently slight influence of particle size on composite strength results from the smaller aspect ratio of the small particles, which indicates that orientation and orientation distribution must have a strong effect on reinforcement. Further improvement in composite strength is possible only through the optimization of particle size, aspect ratio and the inherent strength of wood.     

Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled‐Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, in situ mechanical compression on the transmission electron microscope and aberration‐corrected scanning transmission microscope are unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the calcium carbonate (CaCO₃)‐decorated silica (SiO₂) colloidal capsule. The stiff and brittle nature of the colloidal capsule is due to the interfacial chemical bonding between the CaCO₃ nanoparticles and SiO₂ inner shell. Such bonding strengthens the mechanical strength of the SiO₂ shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO₂ shell (310 ± 70 nm) from the silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat‐treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.     

The filler–rubber interface and reinforcement in styrene butadiene rubber composites with graphene/silica hybrids: A quantitative correlation with the constrained region

Silica/reduced graphene oxide (SiO₂@rGO) hybrids were fabricated by an electrostatic assembly, and subsequently, SiO₂@rGO was incorporated into styrene butadiene rubber (SBR) to fabricate SBR composites. The dispersion status of SiO₂@rGO and the filler–rubber interfacial interaction were investigated. Likewise, the amount of constrained region was quantified and the findings suggested that the greater the volume fraction of constrained region has possessed, the stronger the interfacial interaction has had. Moreover, the contribution of constrained region to the performance of composites was quantitatively analyzed by the mechanical analysis and the tube model, and the results showed that it is the effect of constrained region, rather than the contents of SiO₂@rGO, which controls the reinforcement of composites. Specifically, the higher the volume fraction of constrained region is, the better the mechanical properties of composites will be. Also, SiO₂@rGO can be utilized as novel reinforcing filler for fabricating the green tire materials with high performance.     

茶生物质/聚丙烯复合材料的制备与性能研究

为高值化利用茶产业剩余物资源,以废弃茶生物质(Tea biomass,TB)为填料,聚丙烯(Polypropylene,PP)为基体,采用密炼-注塑工艺制备了TB/PP复合材料,考察了茶生物质填料种类、处理方式及其添加量对复合材料结构、形态及性能的影响。实验结果显示,以茶树枝为生物质填料制备的复合材料力学性能最佳,茶梗次之,茶叶最差;茶梗填料经水煮和马来酸酐接枝聚丙烯增容处理后,复合材料的拉伸强度、弯曲强度、拉伸模量及弯曲模量分别提高了23.4%、9.0%、16.9%和13.9%。SEM图片显示茶梗填料与基体界面相容性提高。随茶梗填料用量的增加,复合材料的拉伸模量、弯曲模量逐渐增大,而拉伸强度及断裂伸长率缓慢下降,吸水率增加,热性能得到改善。当TS添加量为30%(质量分数)时,复合材料的拉伸强度比PP减小7.3%,但弯曲强度、弯曲模量及拉伸模量则分别提高11%、86.1%和54.7%。浸水80h后吸水率为0.89%。     

Influence of filler particle shape on elastic moduli of PP/CaCO3 and PP/Mg(OH)2 composites

The effects of filler particle shape on the Young's and shear moduli of PP/CaCO₃ and PP/Mg(OH)₂ composites were studied in the concentration interval up to 50 vol/vol % filler. Calcium carbonate had irregular, approximately spherical particles and magnesium hydroxide had particles either in the form of hexagonal plates or micro-needles. The analysis based on the classical models together with structural observations enabled explanation of the composition dependences of elastic moduli of the blends studied. It was found that immobilization of PP matrix on the filler surface prominently influenced the values ofG′ andE′ moduli of PP/CaCO₃ and PP/Mg(OH)₂ composites. The presence of the strongly immobilized PP with increasing geometrical anisotropy of the filler particles enabled a hyperstructure creation in the composites PP/Mg(OH)₂.     

Flexural properties and micromorphologies of wood flour/carbon nanofiber/maleated polypropylene/polypropylene composites

The effects of carbon nanofibers (CNF) on the performance of three- or more phase composites are complicated. CNFs formulated into wood flour (WF)/maleated polypropylene (MAPP)/polypropylene (PP) composites by high shear blending alone improved flexural properties. Addition of an extrusion step after high shear blending enhanced CNF dispersion and improved the composites’ flexural moduli, but in these systems CNF did not contribute to flexural property enhancement. The addition of 1.0 wt% CNF to WF/MAPP/PP by high shear blending followed by extrusion did not affect either the WF dispersion or WF/PP adhesion. The adhesion between WF and PP/MAPP matrix was good (SEM), but CNF adhesion to the PP/MAPP matrix was poor.     

Tailoring the tensile/compressive response of magnesium alloy ZK60A using Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

ZK60A nanocomposites containing Al₂O₃ nanoparticle reinforcement were fabricated using solidification processing followed by hot extrusion and T5 heat treatment. Agglomeration of Al₂O₃ nanoparticles was observed in the nanocomposites. However, in the case of ZK60A/1.0 vol%Al₂O₃ nanocomposite (compared to monolithic ZK60A), increase in tensile strength (up to 14%) without significant decrease in ductility and simultaneous increase in compressive strength (up to 12%) and ductility (+23%) were observed. Here, the strength of ZK60A was increased without significant decrease in ductility. On the other hand, in the case of ZK60A/1.5 vol%Al₂O₃ nanocomposite (compared to monolithic ZK60A), simultaneous increase in tensile strength (up to 6%) and ductility (+26%), but decrease in compressive strength (up to 40%) with increase in ductility (+43%) were observed. Here, the ductility of ZK60A was significantly increased without significant increase in strength. This tailoring of tensile and compressive properties of ZK60A via integration with Al₂O₃ nanoparticles are investigated in this article.