Development of self-reinforced polymer composites

This paper reviews the development of single-polymer or self-reinforced composites (SRCs), including the fundamental sciences such as design principles and mechanisms, as well as their preparation techniques and potential application areas. The advantages of such SRC systems include the ability to achieve excellent interfaces between components, their pure chemical functionality, and their higher value as recyclable products due to their relative homogeneity compared to composites composed of different classes of components. Single-polymer composites are particularly important in biomaterials applications, since any additives composed of different chemicals could affect biocompatibility and biodegradation. Various techniques used to design and produce SRCs have been investigated and developed, such as hot compaction, overheating, solution, partial dissolving, cool drawing, physical treatment and chemical modification.     

Quantitative description of interfacial strength in polypropylene/inorganic particle composites

The parameters characterizing the interfacial adhesion strength, such as interaction parameter (B) and interfacial adhesion angle (θ), of inorganic particulate‐filled polymer composites were analyzed in this paper. On the basis of the previous studies and the research work reported in literature, several expressions for predicting these parameters and the determination methods of these parameters were proposed, and the relationship between the interaction parameter and interfacial adhesion angle was discussed. Then the parameters B and θ were estimated from the experimental measured tensile strength of the several inorganic particulate‐filled polypropylene (PP) composites including nanometer calcium carbonate, glass bead and diatomite particles. The results showed that the value of θ was about from 44 to 75 degrees while the value of B was varying from 1.12 to 2.42 of these filled systems under the experimental conditions. Moreover, the value of B decreased roughly linearly with increasing θ for these particulate‐filled PP composites.POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Biofiber-reinforced polypropylene composites

Biofibers, natural lignocellulosics, have an outstanding potential as a reinforcement in thermoplastics. This study deals with the preparation of lignocellulosic composites by reactive extrusion processing in which good interfacial adhesion is generated by a combination of fiber modification and matrix modification methods. PP matrix was modified by reacting with maleic anhydride and subsequently bonded to the surface of the modified lignocellulosic component, in-situ. The fiber surface was modified by reacting it with a silane in a simple and quick aqueous reaction system, similar to that employed for glass fibers. The modified fibers are then extruded with the modified polymer matrix to form the compatibilized composite. The various reactions between the lignocellulosic fiber/filler and modified polymer chains, is expected to improve the interfacial adhesion significantly as opposed to simple mixing of the two components, since new covalent bonds between the fiber surface and matrix are created in the former case. These composite blends were then injection molded for mechanical characterization. Typical mechanical tests on strength, toughness and Izod impact energy were performed and the results are reported. These findings are discussed in view of the improved adhesion resulting from reactions and enhanced polar interactions at phase boundaries.     

Preparation and properties of self-reinforced polypropylene/liquid crystalline polymer blends

The mechanical properties of self-reinforced liquid crystalline polymer/polypropylene (LCP/PP) blends strongly depend on the viscosity ratio of the blend components in the melt. This ratio was determined for PP blends with different commercial LCPs (Vectra A950 and Vectra B950), by means of capillary rheometry, under conditions representative for the blending process during extrusion. It was found that optimal mechanical properties were achieved when the LCP/PP viscosity ratio at 285°C ranges between 2 and 4 at a shear rate of 800–1000s⁻¹. The LCP/PP viscosity ratio appears to be shear stress dependent. This creates the option of fine tuning the LCP droplet deformation process by means of the extrusion rate. This shear stress dependence is more pronounced for PP blends with Vectra B950 than for blends with Vectra A950.     

聚丙烯基复合材料的结晶行为

综述了3类聚丙烯(PP)基复合材料体系包括PP/无机物体系、PP/有机物体系和PP／聚合物体系的结晶行为。阐述了PP基体的结晶结构以及结晶动力学特征,包括添加物对PP的结晶温度、结晶速率及结晶度等的影响;分析了结晶行为对复合材料力学性能的影响。复合材料界面对基体聚合物取向结晶形态及结晶行为的影响等还需进一步研究。     

Structural properties and mechanical behavior of injection molded composites of polypropylene and sisal fiber

Composites based on isotactic polypropylene (PP) and sisal fiber (SF) were prepared by melt mixing and injection molding. The melt mixing characteristics, thermal properties, morphology, crystalline structure, and mechanical behavior of the PP/SF composites were systematically investigated. The results show that the PP/SF composites can be melt mixed and injection molded under similar conditions as the PP homo‐polymer. For the composites with low sisal fiber content, the fibers act as sites for the nucleation of PP spherulites, and accelerate the crystallization rate and enhance the degree of crystallinity of PP. On the other hand, when the sisal fiber content is high, the fibers hinder the molecular chain motion of PP, and retard the crystallization. The inclusion of sisal fiber induces the formation of β‐form PP crystals in the PP/SF composites and produces little change in the inter‐planar spacing corresponding to the various diffraction peaks of PP. The apparent crystal size as indicated by the several diffraction peaks such as L_(110)α, L_(040)α, L_(130)α and L_(300)β of the α and β‐form crystals tend to increase in the PP/SF composites considerably. These results lead to the increase in the melting temperature of PP. Moreover, the stiffness of the PP/SF composites is improved by the addition of sisal fibers, but their tensile strength decreases because of the poor interfacial bonding. The PP/SF composites are toughened by the sisal fibers due to the formation of β‐form PP crystals and the pull‐out of sisal fibers from the PP matrix, both factors retard crack growth.     

Direct transformation of cellulose fibres into self-reinforced composites by partial oxypropylation

Bulk oxypropylation limited to the outer layer of cellulose fibres constitutes a straightforward approach to the preparation of a novel type of composite material made up of a thermoplastic sleeve (matrix) surrounding the unreacted core of the fibres (reinforcing elements).     

Lewis acidic polypropylene for compatibilization of polypropylene/microsilica composites

Polypropylene (PP) was compounded with submicron size silica filler particles (microsilica, μSi) up to 30 wt‐%. In addition, three external compatibilizers, with characteristic functionalities, were studied to examine their influence in the mechanical properties of the PP/μSi composites. As a result, the modulus of the composite increased while the other tensile values deteriorated in correlation with increased filler concentration. The addition of an external compatibilizer reduced this deterioration, but the reduction was dependent on the type of the compatibilizer used. The influence of an acid functionalized compatibilizer was unsubstantial while the fluorosilane and the Lewis acidic phenylsilane functionalized polypropylenes acted as effective compatibilizers. In addition to examining the tensile properties, the toughness of the composites was evaluated as well. The microsilica filler was found to act as toughening agent since the Brittle‐to‐Ductile transition point of the composite increased by 2‐3 orders of magnitude at high filler concentrations. However, this increase in the toughness was rapidly lost when an effective compatibilizer was used to bind the filler with the matrix. This observation was consistent with the common understanding of the filler toughening mechanism, where particle‐matrix debonding is a prerequisite for facilitating the plastic stretch of the polymer ligaments between filler particles. In our case, however, the few filler aggregates in the polymer matrix also played a crucial role. While in uncompatibilized composites the filler aggregates remained passive (could not be seen at the fracture surface), the addition of an effective compatibilizer activated these aggregates to promote crack initiation and/or propagation. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Weathering of polypropylene composites containing weldlines

Abstract

This work deals with the weathering behaviour of polypropylene composites containing fillers with various aspect ratios (glass fibre, talc, and calcium carbonate). Single and double end gated injection moulded bars were exposed outdoors in Campina Grande (Brazil) for periods up to 45 weeks and then characterised using infrared spectroscopy, tensile testing, and surface fractography. The unfilled polymer displayed the highest level of mechanical deterioration, followed by polypropylene containing glass fibre, whereas compounds with talc and calcium carbonate were the most resistant to photodegradation. These results are partially a consequence of the screening effect caused by talc and calcium carbonate at the exposed surface. The results indicated that weldlines make the parts weaker, although the strength loss caused by weathering of double end gated samples was similar to that observed with mouldings produced by single gated injection. It was also observed that the adhesion between glass fibre and the polymer matrix was much reduced after weathering, probably as a result of diffusion of water to the interface.     

纳米二氧化硅改性聚丙烯复合材料研究进展

介绍了近年来纳米二氧化硅改性聚丙烯复合材料的研究进展,综述了纳米二氧化硅粒子表面处理和添加增容剂改性的主要方法,阐述了纳米粒子与聚合物相容性的提高对复合材料各项性能的改善作用,并讨论了不同纳米二氧化硅颗粒结构对复合材料性能的影响,最后展望了其在改善聚合物渗透性、阻燃性、导电性等方面的发展前景。     

Mechanical properties of silver-powder-filled polypropylene composites

Mechanical properties, such as tensile and flexural properties, as well as impact behavior of silver-powder-filled isotactic polypropylene composites were investigated in the composite composition range of 0–5.6 vol% of Ag. Tensile modulus, strength, and elongation at break decreased with incorporation of silver and an increase in silver concentration. Analysis of tensile strength data indicated the introduction of stress concentration and discontinuity in the structure upon addition of Ag particles. Izod impact strength decreased sharply on addition of 0.43 vol % of Ag particles, beyond which the value decreased marginally. Both flexural modulus and strength increased with filler content due to an increase in rigidity. Surface treatment of filler marginally improved mechanical properties. © 1996 John Wiley & Sons, Inc.     

Tensile properties of polypropylene flame-retardant composites

The polypropylene (PP) flame-retardant composites filled with aluminum hydroxide (Al(OH)₃), magnesium hydroxide (Mg(OH)₂), zinc borate (ZB), nanometer calcium carbonate (nano-CaCO₃), and polyolefin elastomer (POE) were prepared using a twin-screw extruder, and the tensile properties were measured at room temperature by means of an electronic universal test machine (Model CMT4104) in this paper, to identify the influence of the flame-retardant content on the tensile properties. The results showed that the tensile strength decreased roughly nonlinearly while the tensile elongation at break decreased nonlinearly with increasing the flame-retardant weight fraction. The Young’s modulus and the tensile fracture strength increased nonlinearly with an addition of the flame-retardant weight fraction. The tensile ductility of PP/Al(OH)₃/Mg(OH)₂/ZB/Nano-CaCO₃/POE composite was the best in the three kinds of the composite systems. Moreover, good agreement was showed between the predictions and the measurements of the tensile strength.     

Mechanical properties of mica-reinforced polypropylene composites

The influence of muscovite mica on the tensile, flexural, and mold shrinkage properties of composites with polypropylene (PP) were investigated. The best results in tensile and flexural properties at room temperature were observed for the physicochemical-treated mica followed by silane-treated mica. The mechanical properties could be correlated with the PP-mica interactions, as observed in the scanning electron microscope (SEM). In the present study, with mica aspect ratio equal to about 30, the optimum performance was obtained for the average flake diameter 80 ⩽ d (μm) ⩽ 280. Finally, the results of coloration and weathering are discussed. It was found that the PP/30 percent mica formulation has superior weathering characteristics over the neat PP resin.     

Structure-property relations in polypropylene mica composites

Polypropylene composite samples with concentrations of mica of 10, 20, 30, 40, 45, 50, and 60 wt percent were prepared under identical conditions by injection molding. The influence of mica concentration on the structure and mechanical properties of the composites was investigated using a polarizing microscope, scanning electron microscope, differential scanning calorimetry, and stress-strain characteristics. Flexural and impact strengths show an initial rise and then gradual fall with increasing mica concentration. An optimum of these properties occurred at ∼20 wt percent mica. Tensile modulus and heat distortion temperature show a continuous rise; whereas the percent elongation decreased with mica content. These changes in properties are discussed in terms of a skin-core morphology, transcrystallinity, crystallinity, fracture surface morphology, flake orientation, and interfacial adhesion in these composites. This study helps in optimizing the mica concentration for injection molded composites.     

PP/木粉复合材料的热性能

以聚丙烯(PP)/木粉(WF)复合材料(WPC)为对象,研究了WF及马来酸酐接枝聚丙烯(PP-g-MAH)含量对WPC热性能的影响。PP和WF的熔融热焓分别为75.84 J/g和189.50 J/g,而w(WF)为10%,20%,30%,40%,50%的WPC的熔融热焓分别为54.99,40.37,38.66,27.34,22.09 J/g,加入PP-g-MAH后,WPC熔融热焓值有所提高。所有WPC在200～750℃的热分解都是分两步完成的,WF含量越高,两步分解现象越明显,第一步失重率越大;WPC每步分解的起始分解温度及峰值温度均有所提高,WPC对热更稳定。     

Torrefied biomass‐polypropylene composites

Torrefied almond shells and wood chips were incorporated into polypropylene as fillers to produce torrefied biomass‐polymer composites. The composites were prepared by extrusion and injection molding. Response surface methodology was used to examine the effects of filler concentration, filler size, and lignin factor (relative lignin to cellulose concentration) on the material properties of the composites. The heat distortion temperatures, thermal properties, and tensile properties of the composites were characterized by thermomechanical analysis, differential scanning calorimetry, and tensile tests, respectively. The torrefied biomass composites had heat distortion temperatures of 8–24°C higher than that of neat polypropylene. This was due to the torrefied biomass restricting mobility of polypropylene chains, leading to higher temperatures for deformation. The incorporation of torrefied biomass generally resulted in an increase in glass transition temperature, but did not affect melting temperature. Also, the composites had lower tensile strength and elongation at break values than those of neat polypropylene, indicating weak adhesion between torrefied biomass and polypropylene. However, scanning electron microscopy results did indicate some adhesion between torrefied biomass and polypropylene. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41582.     

Thermal characteristics of silver powder-filled polypropylene composites

The thermal properties of silver powder-filled polypropylene composites were studied as a function of filler concentration. Thermal conductivities of the composites increased with filler content. Comparison of the data with theoretical predictive models for two-phase systems showed that the Nielson equation agreed reasonably well with the measured values. A TGA study showed that presence of silver powder increased the thermal stability of polypropylene through an increase in activation energy. The thermal expansion coefficient of the composites exhibited a decreased in the presence of Ag powder. Surface treatment of Ag powder with a titanate coupling agent marginally increased thermal conductivity and decreased thermal expansion coefficient values, implying a degree of enhance adhesion of the filler with the polymer. © 1994 John Wiley & Sons, Inc.     

Sulfur-free lignins as composites of polypropylene films

To elucidate the effect of lignin addition, polypropylene films containing 2–10 wt % of spruce organosolv lignin and/or beech wood prehydrolysis lignin were compared with lignin-free polymers with respect to tensile strength and elongation before and after aging. The physicochemical properties of the lignin-containing films were investigated by conductivity measurements, surface behavior, and UV and IR spectroscopy. © 1993 John Wiley & Sons, Inc.     

Tensile properties of polypropylene/kaolin composites

Tensile properties of isotactic polypropylene filled with particulate kaolin fillers were evaluated in the composition range 0–60 wt % kaolin. Tensile modulus increased with filler concentration while breaking elongation and tensile strength decreased. The modulus increase was attributed to the restriction on the molecular mobility of the polymer imposed by kaolin particles. The decrease in elongation was also an effect of this restriction coupled with interference to stress transfer by the filler particles. Generation of discontinuity in the composite structure through formation of stress concentration points accounted for the tensile strength decrease. Morphology studies by SEM also indicated the introduction of stress concentration points by the presence of bare and nonadherent kaolin particles and their agglomerates with sharp edges in these composites.     

Damping behavior of wood filled polypropylene composites

The damping coefficient (tanδ) of wood flour filled polypropylene composites, having varying filler concentrations were measured using the free vibration decay of disk‐shaped specimen, vibrating in flexural vibration mode. The damping coefficients decreased with the increase of filler load in composites. There was no significant difference in damping behavior of composites with and without compatiblizer at low filler level (upto 30%). At higher filler loading (>30%), composites with compatiblizer had lower damping coefficient suggesting improved interfacial adhesion between wood and polypropylene. The damping in composite is attributed to the damping because of the composite constituents and damping at the interface. The damping because of interface was estimated using a model and was found to increase with the increase in filler loading. At higher filler content, damping due to interface in composites with compatiblizer was significantly lower than in composites without compatiblizer suggesting a better interfacial adhesion between the wood filler and polypropylene matrix with compatiblizer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009