Novel automated method for evaluating the morphological changes of cellulose fibres during extrusion-compounding of plastic–matrix composites

A novel method based on fluorescence optical microscopy has been developed for determining the fibre geometrical changes occurring during the melt processing of cellulose-reinforced composites, which are known to be closely related with composite properties. Determination of these changes is still a tedious and challenging task because existing methods are not well developed yet. The novel method proved its ability for explaining the screw configuration effects on the attrition bore by the fibres during extrusion-compounding of plastic–matrix composites. The percentage of fibres longer than the critical length parameter was revealed to highlight the mechanical degradation of fibres during compounding. The percentage of fines exhibited the clearest correlation with the differences in fibre content of composites. Relationships found between composite tensile properties and fibre characterization parameters revealed the ability of the novel method for explaining the effects of composition and processing on composite properties.     

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.     

A non-destructive X-ray microtomography approach for measuring fibre length in short-fibre composites

An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting the biasing effects caused by the finite sample size as defined by the limited field of view of the tomographic devices. The method is first tested for computer generated fibre data and then applied in analyzing the fibre length distribution in three different types of wood fibre reinforced composite materials. The results were compared with those obtained by an independent method based on manual registration of fibres in images from a light microscope. The method can be applied in quality control and in verifying the effects of processing parameters on the fibre length and on the relevant mechanical properties of short fibre composite materials, e.g. stiffness, strength and fracture toughness.     

Effect of kneading process conditions on the particle fineness and the polydispersity in nanocomposites

This paper is part of a series of publications that cover the entire process chain to produce nanocomposites. The associated papers are published in the chronological sequence and broach the issues of: “production and dispersing of nanoparticles”, “characterisation of the liquid and reactive matrix” as well as “resulting composite properties by experimental and simulation methods”. Nevertheless, all resulting composite properties are strongly dependent on the method of particle incorporation and on the particle size distribution. Therefore, this study focuses on the optimisation of the dispersion referring to finest particles, smallest particle size distribution, shortest dispersing time and lowest specific energy. In order to prepare the matrix suspension, nano-fillers were dispersed conducting shear mixing techniques in a high performance laboratory kneader. As carrier fluid epoxy resin and a corresponding anhydride hardener system were chosen. Tests were performed using neat and surface modified alumina particles at different levels of particle concentrations. The particle size distribution was determined using dynamic light scattering directly after the dispersing process. Additionally each sample was characterised after 1, 3 and 7 days. Since similar examinations were performed for all formulations, a statement on the influence of re-agglomeration processes and the role of surface modification can be derived. By correlating the progress of the dispersing process to the mass fraction and the particle size distribution, the dispersion process can be evaluated regarding the dispersing time, specific energy and product quality. However, an optimum polydispersity can be found between 25 and 30 wt.%, even if the finest average particle size is reached at higher mass fractions around 45 wt.%. Silane modified alumina particles in epoxy resin constitute the most stable system against re-agglomeration, although the finest particles and the smallest specific energy are attained in non-modified systems. Moreover it can be concluded, that resulting properties of the cured composite are strongly related to the aspired optimisation, e.g. product fines, particle size distribution, required energy input and stability.     

Effect of particle size in Ni screen printing paste of incompatible polymer binders

Dispersion of nano-sized particles at high solid content has attracted attention in many industrial applications such as printed electronic products. However, the material design and processing heavily depends on experience with little quantitative measure. For fabrication of thinner dielectric layers, Ni size is getting smaller when used as an inner electrode in multilayer chip capacitor (MLCC). In the present study, we investigate the rheological properties and printing performance of the pastes with two different sizes of Ni particles in the same incompatible binder mixtures of ethyl cellulose (EC) and polyvinyl butyral (PVB). The difference in particle size causes different microstructural heterogeneity and highly nonlinear rheological properties upon the external flow field. The printing pattern and the surface profile are also analyzed by confocal images after screen printing. For smaller particle size of Ni, the more heterogeneous microstructure is observed with increasing PVB content, which is evidenced by the screen printing images as well as its rheological behavior. We explain the difference of spatial heterogeneity in terms of different interactions between particle–particle and particle–polymer. This work is believed to contribute to better design of inner electrodes and processing in MLCC manufacturing.     

The effect of particle size distribution on barite reduction

The present study is a follow-up of investigation on barite reduction to barium sulfide as a function of starting particle size distribution and temperature of reaction. In this work we study the high temperature reduction process of barite from the view point of particle size distribution. Conversion-time data have been obtained using iodometry method in each isothermal condition. A modified kinetic model used to express the carbothermic reduction process. To obtain the values of activation energy and frequency factor, the same expression was selected for each sample at all temperatures. The rate of reaction is found to be related to the particle size distribution and the gasification reaction of coke which has influence on reduction process. The kinetic parameters calculated from standard analysis of isothermal kinetic data indicated that the particle size of barite controlled the reaction when it was coarser than 400 mesh both in presence and absence of catalyst.     

Development of green composite consists of woodchips, bamboo fibers and biodegradable adhesive

From the viewpoint of the effective utilization of waste wood, the green composite which is produced by solidifying woodchips has been developed [Miki M, Takakura N, Kanayama K, Yamaguchi K, Iizuka T. Effects of forming conditions on compaction characteristics of wood powders. Trans Jpn Soc Mech Eng C 2003;69(678):502–8 [in Japanese]; Miki M, Takakura N, Kanayama K, Yamaguchi K, Iizuka T. Effects of forming conditions on flow characteristics of wood powders. Trans Jpn Soc Mech Eng C 2003;69(679):766–72 [in Japanese]; Miki M, Takakura N, Iizuka T, Yamaguchi K, Kanayama K. Possibility and problems in injection moulding of wood powders. Trans Jpn Soc Mech Eng C 2004;70(698):2966–72 [in Japanese]]. Since the composite was solidified by the compressive load without the binder, it did not have the high strength and was very brittle, and it had no water resistance [Kinoshita H, Kaizu K, Koga K, Tokunaga H, Ikeda K. In: Proceeding of the Japan Society of Mechanical Engineers M& M2007; 2007. CD [in Japanese]]. In this study, to improve these defects, it was proposed that a biodegradable resin as an adhesive and bamboo fibers as reinforced fibers were applied to the woodchip composite. By using woodchips with two kinds of the particle size, bamboo fibers with three kinds of the length and the biodegradable adhesive, several kinds of specimens changed mixing ratio of those materials were produced by compression molding at the appropriate temperature. By examining the bending strength and impact strength of the composites, it was found that the high bending strength was obtained in the case where woodchips with the small particle size and long bamboo fibers were used, and the high impact strength was obtained in the case where woodchips with the large particle size and long bamboo fibers were used.     

Abrasive wear of Al2O3-reinforced aluminium-based MMCs

The effects of volume fraction, Al₂O₃ particle size and effects of porosity in the composites on the abrasive wear resistance of compo-casting Al alloy MMCs have been studied for different abrasive conditions. It was seen that porosity in the composites is proportional to particle content. In addition, process variables like the stirring speed, and the position and diameter of the stirrer affect of the porosity content in a way similar to that observed for particle content. In addition, the abrasive wear rates of composites decreased more rapidly with increase in Al₂O₃ volume fraction in tests performed over 80 grade SiC abrasive paper than in tests conducted over 220 grade SiC abrasive paper. Furthermore, the wear rates decreased with increase in Al₂O₃ size for the composites containing the same amount of Al₂O₃. Hence, it is deduced that aluminium alloy composites reinforced with larger Al₂O₃ particles are more effective against abrasive wear than those reinforced with smaller Al₂O₃ particles. At the same time the results show that the beneficial effects of hard Al₂O₃ particles on wear resistance far surpassed that of the sintered porosity in the compocasting metal-matrix composites (MMCs). Nevertheless, the fabrication of composites containing soft particles such as graphite favors a reduction in the friction coefficient. For this reason graphite and copper were used in the matrix in different amounts to detect their effect on wear resistance. Finally, it was seen that wear rate of the composites decreased considerably with graphite additions.     

粉料包装机计量螺杆的结构参数优化设计

目的 在不改变螺杆转速和外径的前提下，对已有包装机的计量螺杆结构参数进行优化设计，提高计量螺杆的输送效率。方法 构建螺杆的输送能力模型，并分析颗粒在计量螺杆内部的运动速度。通过电镜显微镜观测典型物料颗粒微观形貌，在离散元仿真环境中构建颗粒形貌，并模拟粉状物料的计量输送过程。通过比对不同结构参数的计量螺杆输送能力，得到初选结构参数，基于粒子群优化算法得到螺杆最佳结构参数，通过仿真模拟方法对优化后的计量螺杆输送能力进行比对验证。结果 优化后的计量螺杆对粉状物料输送速度为358.79 mm/s，输送效率提高了7.44%。结论 通过优化结构参数和仿真模拟结合的方法，提高了粉状物料计量螺杆的输送效率，为工业企业计量螺杆的设计和加工提供基础数据参考。     

Sliding wear behaviour of SiC particle reinforced 2024 aluminium alloy composites

Abstract

Sliding wear tests on SiC particle reinforced 2024 aluminium alloy composites fabricated by a powder metallurgy technique were carried out, and the effects of SiC particle content, size, and the wear load on the wear properties of the composites were systematically investigated. It was found that the wear resistance of the composites was about two orders of magnitude superior to that of the unreinforced matrix alloy, and increased with increasing SiC particle content and size. Under the conditions of sliding wear used, the effect of SiC particle size on the wear resistance was more significant than that of particle content.

MST/3161     

Process intensification in particle technology: Intensive granulation mechanism and granule characteristics

The mechanism and processing characteristics of a novel intensified granulation technique are evaluated. This intensification technique is based on the non-isothermal flow induced phase inversion (FIPI) phenomenon. Poly(ethylene glycol) (PEG) with an average molecular weight 10⁴ and calcium carbonate powder (mean particle size 2.7 m) were used as binder and filler to prepare granules. The granulation experiments were carried using a Haake extruder (Rheomex 252) which connected to a granulator of a new design. The extruder produced a homogenous PEG and calcium carbonate paste and fed it to the granulator. When the paste was subjected to a temperature gradient field with a superimposed repeated shear and extensional deformation, solidification, granule nucleation and subsequent macroscopic fragmentation (referred to as crumbling) occurred to give granular particles. The mechanism of granulation has been discussed. The granule size and size distribution characteristics under different process conditions have been evaluated. The novelty of this research lies in the granulator design and the mechanism of the granulation process. Temperature differential and repeated deformation are the two primary factors for the granulation process. Particle size distribution and crumbling area depend on the concentration of PEG, the clearance between rotor and stator, and the extrusion speed. If a so called crumbling agent, in the form of fine particles, is added to the newly formed granules, these granules are coated with the crumbling agent forming a core-shell type of granulated particles.     

Wood based PLA and PP composites: Effect of fibre type and matrix polymer on fibre morphology,dispersion and composite properties

This study presents a comparison of the effect of various wood fibre types in polylactic acid and polypropylene composites produced by melt processing. The study also reveals the reinforcing effect of pelletised wood fibres compared to conventionally used wood flour or refined fibres. Composites containing 30 wt.% of chemical pulps, thermomechanical pulp and wood flour were produced by compounding and injection moulding. Fibre morphologies were analysed before and after melt processing. The dispersion of the fibres and mechanical performance of the composites were also investigated. Fibre length was reduced during melt processing steps, reduction being higher with longer fibres. Wood fibres provided clearly higher plastic reinforcement than wood flour. Comparing the wood fibre types, TMP fibres provided the highest improvement in mechanical properties in polylactic acid composites with uniform fibre dispersion. In polypropylene composites, fibre selection is not as crucial.     

The effect of pre-softened wood chips on wood fibre aspect ratio and mechanical properties of wood–polymer composites

The objective of this work was to study the effect of chemical pre-treatment and moisture content of wood chips on the wood particle aspect ratio after compounding in a twin-screw extruder and on the mechanical properties of wood–polymer composites (WPCs). Composites with 50 wt.% wood content were manufactured using pre-treated and untreated wood chips. The effect of wood moisture content on composite properties was studied by using dried and undried wood chips. The mechanical properties and fracture surfaces of the composites as well as the microstructure and aspect ratio of wood particles after compounding were studied. The highest wood particle aspect ratio after extrusion was achieved by using pre-treated, undried wood chips as raw material. The chemical pre-treatment was found to enhance the defibration of wood chips as well as the mechanical properties of the composites.     

An enhanced FEM model for particle size dependent flow strengthening and interface damage in particle reinforced metal matrix composites

By incorporating the dislocation punched zone model, the Taylor-based nonlocal theory of plasticity, and the cohesive zone model into the axisymmetric unit cell model, an enhanced FEM model is proposed in this paper to investigate the particle size dependent flow strengthening and interface damage in the particle reinforced metal matrix composites. The dislocation punched zone around a particle in the composite matrix is defined to consider the effect of geometrically necessary dislocations developed through a mismatch in the coefficients of the thermal expansion. The Taylor-based nonlocal theory of plasticity is applied to account for the effect of plastic strain gradient which produces geometrically necessary dislocations due to the geometrical mismatch between the matrix and the particle. The cohesive zone model is used to consider the effect of interfacial debonding. Lloyd’s experimental data are used to verify this enhanced FEM model. In order to demonstrate flow strengthening mechanisms of the present model, we present the computational results of other different models and evaluate the strengthening effects of those models by comparison. Finally, the limitations of present model are pointed out for further development.     

Evolution of lignocellulosic fibre lengths along the screw profile during twin screw compounding with polycaprolactone

Composites made of polycaprolactone reinforced by 20% hemp fibres were prepared by melt blending in a twin screw extruder (TSE). The influence of the extrusion parameters (feed rate and screw speed) on the fibre length evolution along the screw profile was investigated. The fibre length rapidly decreased after the introduction of the fibres and during the flow through the kneading blocks. Fibre fragmentation was increased at high screw speeds and low feed rates. The flow conditions along the TSE were calculated using Ludovic© software, focusing on the specific mechanical energy (SME) provided to the fibres. The fibre length evolution can be correctly estimated for various flow conditions using an exponential function of the SME.     

The role of particle size and polymer molecular weight in the formation and properties of an organo-ceramic composite

The role of particle size and polymer molecular weight in the formation and properties of a calcium aluminate cement-poly(vinyl alcohol) composite was investigated. Banbury mixing studies, in combination with poly(vinyl alcohol) solution rheology, showed paste formation to be dependent on the polymer degree of polymerization and concentration. Both polymer molecular weight and cement particle size have an effect on the mechanochemistry, the window of processibility, and mechanical properties of the hardened matrix. Increasing the polymer chain length appears to accelerate the mechanically induced crosslinking reactions between the polymer and cement hydration phases, thereby diminishing the processing window. Decreasing the cement mean particle size has a similar effect. Polymer degree of polymerization and cement particle size distribution are shown to be important factors in the mechanical properties of the hardened composite. Scanning electron microscopy (SEM) micrographs show that wide polydispersity in the grain phase is important in attaining a macro-defect-free microstructure.     

Optimization of electrophoretic deposition of alumina onto steel substrates from its suspension in iso-propanol using statistical design of experiments

Statistical design of experiments was used to investigate the effect the process parameters on electrophoretic deposition (EPD) of alumina onto steel substrates from its suspension in iso-propanol. The process parameters considered were (i) concentration of particles in the suspension (solid loading), (ii) electrode separation, (iii) applied potential, and (iv) deposition time on the quantity of ceramic particles electrophoretically deposited. A 2⁴ full factorial matrix, with four repetitions of the center point, was used to develop the predictive regression equation for deposition of alumina per unit area of the electrode in the design space. The results show that particle concentration has the most dominant effect with more than 50% contribution to the deposited amount. A good correlation was obtained between predicted and experimental values suggesting that the model can predict data accurately in the experimental matrix.     

Determination of particle size distributions and the degree of dispersion in nanocomposites

Objective of this study was the investigation of measurement techniques to determine the quality of the dispersion process of nanoparticles in polymer composites. In order to prepare the matrix suspension, alumina nanoparticles were dispersed applying shear mixing techniques in a high performance laboratory kneader. The product quality in liquid state was determined by means of dynamic light scattering (DLS) and centrifugal sedimentation analysis (CSA). However, particle measurements in carrier fluids like epoxy resin are complex and challenging. Measuring values like particle size distribution and grade of homogeneousness are strongly influenced by the sample preparation and adjustments of the measuring device. Within this study the machine settings and the formulation was analysed systematically. Hereby an identification of the key parameters and an optimisation of the measuring process were possible. Additionally, the composite was cured and analysed by scanning electron microscopy (SEM). Finally all measuring techniques were evaluated and compared among each other. Thus, DLS is the fastest method to measure spherically particles in the liquid matrix, CSA allows a certain deviation from the spherical shape and SEM gives a qualitative impression of the final particle size in cured composite condition.     

Die drawn wood polymer composites. II. Micromechanical modelling of tensile modulus

The Cox–Krenchel micromechanical model was applied to give predictions for the tensile moduli of isotropic and oriented wood polymer composites (WPC). The oriented WPC were produced by the Leeds die-drawing process using polypropylene filled with softwood and hardwood powders. The wood particles were extracted from the composites to determine their density and aspect ratio by dissolving in hot decalin. To measure particle shape and size, image analysis was employed. These experimental parameters were then introduced to the Cox–Krenchel model which was found to give prediction of tensile modulus in very good agreement with the experimental values.     

The influence of particle orientation on the loading condition of pebbles in fluvial gravel

The loading conditions of pebbles in fluvial gravel deposits were studied with different degrees of preferred particle orientation. Sediments that are comprised of non-spherical particles often show a preferred particle orientation, due to dynamic sedimentation. Here, the impact of this effect on the loading conditions of the particles and its implication on particle breakage was investigated by using discrete element simulations in three dimensions. The numerical models are based on the size and shape distribution of pebbles from a natural gravel sample. In addition, the particle size in some of the models was chosen to be uniform, to study the influence of the particle size distribution on the loading condition. Fluvial pebbles, whose shapes can be at best approximated by ellipsoids, were efficiently simulated in the discrete element models by the use of clumps. The results show that a preferred orientation of approximate ellipsoidal sedimentary particles has only a minor effect on the number and the position of particle contacts but leads to a significant load transfer from the rim to the centre of the oblate sides of the ellipsoidal particles, in comparison to an assembly of arbitrarily oriented particles. The comparison of the different particle size models indicates that the influence of the particle size distribution on the loading condition is relatively low. The results have significant implications for the breakage rate of non-spherical particles in sediments under load.