No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Dynamic particle analysis for the evaluation of particle degradation during compounding of wood plastic composites
Abstract
A dynamic image analysis method was applied for particle characterisation to study the effect of different process conditions during twin-screw compounding of WPC. The use of distributions based on different types of quantity is discussed with respect to their sensitivity to reveal the effects of different process conditions on particle degradation. Distributions based on length proved to be most suitable to represent the initially broad length distribution of the particles before processing. Sensitivity was strong enough to show differences in particle size after processing depending on process conditions. Particle size was reduced by more than 97% compared to initial size. Degradation was stronger with increasing wood content and when the screw design contained more mixing elements. The effect of screw speed and feed rate was dependent on filler content and screw design.
... Degradation, the rate of which depends strongly on the exposure temperature, starts at approx. 170 • C, depending on the cellulose content of the NF [12,13], and results in a reduction in mechanical properties [14][15][16][17][18]. The pure cellulose fibers are thermally more stable and show significant material degradation in thermogravimetric analyses only from 240 • C due to a measured loss of mass [19][20][21][22]. ...
... Higher temperature exposure leads to degradation phenomena, which occur in RCF from about 220 • C due to the breaking of chemical bonds [19,65]. Overall, pure cellulose (e.g., RCF) exhibits higher heat resistance compared to conventional natural fibers [12,13,66]. With the onset of the degradation processes, the tensile strength of the RCF and especially the elongation at break decreases. ...
The increasing demand for renewable raw materials and lightweight composites leads to an increasing request for natural fiber composites (NFC) in series production. In order to be able to use NFC competitively, they must also be processable with hot runner systems in injection molding series production. For this reason, the influences of two hot runner systems on the structural and mechanical properties of Polypropylene with 20 wt.% regenerated cellulose fibers (RCF) were investigated. Therefore, the material was processed into test specimens using two different hot runner systems (open and valve gate) and six different process settings. The tensile tests carried out showed very good strength for both hot runner systems, which were max. 20% below the reference specimen processed with a cold runner and, however, significantly influenced by the different parameter settings. Fiber length measurements with the dynamic image analysis showed approx. 20% lower median values of GF and 5% lower of RCF through the processing with both hot runner systems compared to the reference, although the influence of the parameter settings was small. The X-ray microtomography performed on the open hot runner samples showed the influences of the parameter settings on the fiber orientation. In summary, it was shown that RCF composites can be processed with different hot runner systems in a wide process window. Nevertheless, the specimens of the setting with the lowest applied thermal load showed the best mechanical properties for both hot runner systems. It was furthermore shown that the resulting mechanical properties of the composites are not only due to one structural property (fiber length, orientation, or thermally induced changes in fiber properties) but are based on a combination of several material- and process-related properties.
... The use of reverse screw elements increases the shear rate and the severity of the process (Gogoi et al., 1996). Shearing increases with mixing or kneader elements , as reported for bast fibre, and also short wood fibre (Dickson et al., 2020); inducing a drastic reduction in the length of the fibres (Teuber et al., 2016). The screw profile also influences the final properties of composites. ...
... Cadmould® and MoldFlow®) and determine fibre interaction coefficients (Albrecht et al., 2018) that reflect the adhesion forces between the fibres within fibre bundles. When the volume fraction (and thereby concentration) of plant fibre increases, the fibre lengths and diameters decrease, as shown for wood (Teuber et al., 2016) and flax (Puglia et al., 2008). These trends were confirmed experimentally by Ausias et al. (Ausias et al., 2013a(Ausias et al., , 2013b. ...
Over the past decades, the use of plant fibre reinforced composites has increased significantly due to their many attractive attributes such as high specific strength and modulus, wide availability, low cost and high environmental credibility compared to their synthetic counterparts. These attributes are especially attractive for lightweight applications in automotive, marine, aerospace and sporting goods sectors. This growth is expected to continue in the future. To improve the design and performance of bio-based composites, an improved understanding of processing-structure-property relations in such bio-based composites is required, the fibres being the key component of the composite to obtain performing properties. This is due to the sensitivity of the constituent plant fibres to mechanical stress (pressure), temperature, water and other parameters. The purpose of this review is to critically synthesise literature on the impact of composites processing steps on plant fibre cell wall structure and properties. The impact of plant fibre composites processing steps from the polymer impregnation stage right through to the end-of-life recycling stage is reviewed. Additionally, mechanical, morphological and hygroscopic properties of plant fibres are considered in conjunction with process times, temperature and shear rate. This review will aid process and product designers to develop new performing plant fibre composite products, taking into account the process parameters to select the most optimised process and (their effects on) plant fibres. Considering how fibre properties change with biocomposites processing steps is indeed essential to understanding the links between the micro and macro scales, and to be able to design optimised plant fibre composite materials.
... Validation of the experimental procedure First, a comparison between the number and volume length distributions is proposed in order to determine a valuable method of particle size analysis using the dynamic analyser used (QICPIC). Particle morphology analysis provides significantly different information depending on measurement parameters such as equipment used, image resolution, automatic or "by-hand" measurements, causing specific particle size populations to be potentially left out (Le Moigne et al., 2011;Teuber et al., 2016;Haag and Müssig, 2016). ...
... Le Moigne et al. (Le Moigne et al., 2011) found that 'by hand' measurements induced a discrepancy and had a tendency to magnify fibre dimensions due to operator dependence compared to using a specific software for fibre detection (50 % of the number weighted length of flax fibres measured by hand were more than twice the length of the same particles detected by the software). Dynamic image analysis is a time-efficient method to obtain a wide amount of particle morphology information such as shape descriptors and distributions in number, length, surface or volume (Teuber et al., 2016). In the rest of this study, analysis is carried out on the basis of volume distributions. ...
Flax shives (FS) represent approximately 50 % in weight of dry flax stems, making it the main by-product of the flax scutching industry. Being an available and low-added value lignocellulosic resource, flax shives are an interesting candidate for thermoplastic composite reinforcement. In this study, raw flax shives were fragmented by knife milling using two grids of 500 and 250 μm respectively, while a third batch, with a targeted particle size below 50 μm, was obtained by an attrition beads mill. The fragmentation methods used do not modify the biochemical composition of FS but do reduce their crystallinity due to both crystalline cellulose allomorph conversion and amorphization. The poly-(propylene) and 4%-wt maleic anhydride modified poly-(propylene) injection moulded composites produced with these reinforcing materials have a maximum tensile strength that evolves linearly with particle aspect ratio after processing. The tensile Young’s modulus of the composites reinforced by coarser particles is 3268 ± 240 MPa, which is almost 90 % that obtained for a reference 1mm flax fibre reinforced composite. Furthermore, a basic micromechanical model was applied highlighting the reinforcing capacity of cell wall-like small tubular structures (e.g. flax shives). This study underlines the reinforcing potential of low-value by-product flax shives for value-added composite applications.
... Wood particulates have dimensions that are approximately equal in all directions and can be of any shape [16], they act mainly as fillers. However, the initial wood component morphology is not constant throughout WPC processing, but it is prone to changes due to shear forces and high temperatures, particularly during the compounding with twin screws in an extruder [19][20][21]. ...
... In the device, the wood particles are dispersed in an accelerated air jet and a high-speed camera takes pictures of the particle stream with a resolution of 10 µm and 20 µm. WINDOX software (Sympatec GmbH, Clausthal-Zellerfeld, Germany) was used to measure the particle size from the projected particle area of binary pictures [20]. The particle size was characterized with respect to the median (x 50 ) and quartiles (x 25 ; smallest and x 75 ; largest) of the length-based particle size distribution (Q1). ...
The objective of this study is to evaluate and compare the mechanical and water-related properties of WPC containing two types of recovered wood particles. These particles were obtained by thermo-hydro-mechanical and sole mechanical (milling) disintegration and compared to virgin wood fibres. The respective composites were produced with and without maleic anhydride-grafted polypropylene (MAPP) as a coupling agent. The results clearly show that both types of particles, which derive from end-of-life MDF are a suitable resource to produce WPC. The physico-mechanical characteristics of the WPC containing particles from thermo-hydro-mechanical disintegration were statistically better than those containing mechanically produced particles.
... KG, Duisburg, Germany) and a hot-cut pelletizer. A screw design with well distributed kneading elements (design A) was used [45]. The TSE is equipped with 10 heating barrels. ...
... Besides other factors (e.g., particle dispersion, orientation and matrix adhesion), particle length and aspect ratio are major factors effecting the reinforcing efficiency of fibrous lignocellulosic particles in the polymer matrix. In accord with previous studies on wood particle/fibre degradation due to processing [44,45,51,52], length and aspect ratio of particles are remarkably reduced by extrusion and injection moulding. In our study, however, we obtained retained particle length and aspect ratio values after extracting the particles from the polypropylene matrix. ...
In this study, various wood material sources were used for the manufacture of wood-polymer composites (WPC). The materials were categorised as virgin wood particles (VWP), reprocessed WPC particles (RWP) and recycled thermoset composite particles (RCP) and derived from two virgin wood sources, three-layer particleboards, medium-density fibreboards (MDF) boards, or two different wood/polypropylene composites. All produced wood-polypropylene compounds contained 60% wood material and were manufactured using a co-rotating extruder. Malleated polypropylene was used as a coupling agent. Specimens were injection moulded and subsequently tested for their physico-mechanical properties. To characterize particles before and after processing, dynamic image analysis (DIA) measurement were performed. Additionally, X-ray micro-computed tomography (XµCT) was used to characterize the internal structure of the composites and to verify the obtained particle’s characteristics. It was found that length and aspect ratio of particles were remarkably different before and after processing (loss in length of 15–70% and aspect ratio of 10–40%). Moreover, there were notably differences between the particle sources (RCP retained the highest length and aspect ratio values, followed by VWP and RWP). The results suggest that increased aspect ratios can indeed significantly improve mechanical properties (up to 300% increase in impact bending strength and 75% increase in tensile strength, comparing WPC based either on virgin spruce or MDF material). This phenomenon is suggested to be partially superimposed by improved dispersion of particles, which is expected due to lower variance and increased mechanical properties of RWP composites. However, no notable alterations were observed for composite density. Reprocessed WPC and, particularly, RCP material have proved to be an appealing raw material substitute for the manufacturing of wood–polymer composites.
... That is why, the utilization of wood fibres instead of wood flour as reinforcement in WPC has gained interest in recent years (Lerche et al. 2014;. Severe fibre length reduction, however, occurs during the composite preparation because of the chosen raw material feeding method, low polymer melt flow rate and increasing screw speed in the twinscrew extruder as well as high shear forces during the injection moulding process (Teuber et al. 2016a(Teuber et al. , 2016b. ...
... In the device, the wood fibre particles were dispersed in an accelerated air jet and a high-speed camera took pictures of the particle stream with a resolution of 10 and 20 µm. Measuring particle size and shape from the projected particle area of binary pictures and calculating size and shape distributions were done by the software WINDOX (Sympatec GmbH, Clausthal-Zellerfeld, Germany) (Teuber et al. 2016a). Fibre length was characterized with respect to the median (x 50 ) and quartiles (x 25 and x 75 ) of the length-based particle length distribution (Q1). ...
In most countries, fibreboards are not recovered after utilization but burned for energy production. This study aims at recovering fibres from industrial fibreboards and reusing them as reinforcement elements in wood polymer composites (WPC). Recovered fibre (RF) material was generated by the thermo-hydrolytic disintegration of medium and high density fibreboards bonded with urea-formaldehyde resin. Various formulations of RF and polypropylene were used with or without the addition of the coupling agent to manufacture WPC using a co-rotating extruder. Test specimens were produced via injection moulding whereby those containing ‘virgin’ fibres served as a reference with respect to mechanical and physical properties. WPC formulations containing RF and ‘virgin’ fibres exhibited similar results, but composites containing RF exhibited improved mechanical and water-related properties, especially without coupling agent. The study indicates that recovered fibres are suitable to produce WPC with very similar physico-mechanical properties as those from ‘virgin’ fibres.
... Thus, automatic dynamic image analysis is of interest, since it avoids human bias (Di Giuseppe et al., 2016) and can be used to measure the size of a large number of particles that can reach several millions per batch (Nuez et al., 2020c). Moreover, it prevents the particles from sticking together, which makes it possible to obtain highly reliable statistical results (Teuber et al., 2016). ...
Residual shives have a major impact on the quality and performance of flax textile and composite preforms. Quantifying the content of shives in batches of scutched flax fibres is a time-consuming and operator-dependent process. Although the shive content can be estimated from the chemical composition, our aim here is to explore a series of effective, reliable and complementary approaches to quantifying shives. Various methods are presented: microscopic observations, analytical biochemistry (monosaccharides, lignins), indirect methods (infrared spectroscopy) and dynamic morphological analysis (QICPIC). A reference standard was first analysed and then compared with batches of flax tow fibre of unknown shive content from current industrial production. This approach shows that calibration curves can be established by applying each selected method to batches with known fibre and shive content. In addition, a database was generated to determine the shive content of industrial batches using partial least squares (PLS) regression. Finally, a detailed study of shives in industrial batches is presented, comparing the different analytical methods.
... 16 Teuber et al. analysed the dynamic particle degradation during compounding and reported bre reduction throughout processing with high bre content. 17 The inuence of the kind of plant bre on the mechanical properties of biocomposites was reported by Feng et al. 18 Wu et al. concluded that adding maleic anhydride as coupling agent led to the improvement of alkalised sisal bres reinforcing maleated PP, and the exural strength of the composite and the nal bre morphology inuenced the mechanical properties. 19 Although natural bre composites have been reported under the inuence of alkaline treatment and extrusion, there are few works of those techniques when wood bres (or our) reinforce PLA and are posterior injection moulded. ...
Natural fibres are promising candidates for polymer reinforcement due to their specific properties and renewability. To investigate the influence of wood fibre (WF) alkaline treatment on the mechanical properties of wood-plastic composites (WPCs), alkalised and raw WF-reinforced polylactic acid composites (40/60 wt%) were compounded using two different lengths of WF (100 and 400 μm) in the presence of maleic anhydride as the coupling agent. The structural analysis confirmed the removal of lignin and hemicellulose components from the fibres. The reinforcement increased the tensile and flexural moduli up to 140% and 137%, respectively, in the presence of a coupling agent. For raw fibre-reinforced composites, the tensile and flexural strengths increased by 12% and 12%, respectively. In contrast, alkalised fibres showed inferior performance, suggesting that the removal of hemicellulose and lignin added to the shear forces during extrusion led to their mechanical loss. Although all composites showed a decreased impact strength, the short fibre composites increased their properties by adding maleic anhydride. It can be clearly shown that short fibre-reinforced PLA performed mechanically better than the long counterparts and that the alkaline treatment did not produce better outcomes than the pristine raw fibres.
... The procedure works with the MIXCEL liquid dispersion unit, which uses isopropanol as the carrier medium of the fibers. The fibers were previously extracted from the matrix using a simplified soxhlet extraction [29]. Small pieces of the parallel section of a 1A test specimen and highly concentrated (98%) formic acid were placed into a beaker at 23 • C for 5 h to dissolve the bio-polyamide matrix. ...
With regard to the sustainability and biological origin of plastic components, regenerated cellulose fiber (RCF)-reinforced polymers are expected to replace other composites in the future. For use under severe conditions, for example, as a housing in the engine compartment, the resistance of the composites and the impact on the fiber and fiber-matrix adhesion must be investigated. Composites of bio-polyamide with a reinforcement of 20 wt.% RCF were compounded using a twin-screw extruder. The test specimens were manufactured with an injection molding machine and aged under conditions of high humidity at 90% r. H, a high temperature of 70 °C, and water storage using a water temperature of 23 °C for 504 h. Mechanical tests, single-fiber tensile tests (SFTT), single-fibre pull-out tests (SFPT), and optical characterization revealed significant changes in the properties of the composites. The results of the SFPT show that accelerated aging had a significant effect on the bio-polymer and an even stronger effect on the fiber, as the single-fiber tensile strength decreased by 27.5%. Supplementary notched impact strength tests revealed a correlation of the impact strength and the accelerated aging of the RCF-reinforced composites. In addition, it could be verified that the tensile strength also decreased at about 37% due to the aging effect on the RCF and a lowered fiber-matrix adhesion. The largest aging impact was on the Young’s modulus with a decrease of 45% due to the accelerated aging. In summary, the results show that the strengthening effect with 20 wt.% RCF was highly decreased subsequent to the accelerated aging due to hydrolysis and debonding because of the shrinkage and swelling of the matrix and fiber. These scientific findings are essential, as it is important to ensure that this bio-based material used in the automotive sector can withstand these stresses without severe degradation. This study provides information about the aging behavior of RCF-reinforced bio-based polyamide, which provides fundamental insights for future research.
... The fiber dimensions are generally characterized by 3D-microtomography [107,108] or by 2D image analysis after dissolution of the matrix. Different techniques may be employed, which are more or less accurate depending on the case considered [109][110][111]. Usually, size distributions of length L, diameter D and aspect ratio L/D are measured over a population of at least a few hundred fibers, and average values are derived from these distributions. ...
... Approximately 150,000 fibers were measured for each sample. The parameter LEFI is defined as the shortest distance between the most distant endpoints of a fiber [21]. Images were taken with a frame rate of 175 Hz and a resolution of 4.2 MP using an M4 magnification, which results in a pixel size of 4.2 µm [22]. ...
The fiber type, orientation of the fiber, fiber-matrix adhesion, and the fiber length are very important for the performance of a short fiber reinforced plastic. Hybrid reinforced polybutylene terephthalate and reference compounds were tested using tensile, Charpy impact, and three-point bending mechanical tests. The interaction of regenerated cellulose fiber and glass fiber was investigated using a polybutylene terephthalate matrix at a fiber volume content of 10%. The ratios of each fiber type was varied. The compounds were pultruded with an extrusion die to have an even fiber length of 3 mm after granulating. In a second step, the specimens were injection molded for mechanical testing. The results were compared to the rule of hybrid mixtures (RoHM) prediction. It was shown that the results of the hybrid reinforced compound were close to the RoHM prediction. The Charpy impact tests show a high positive hybrid effect. The fiber length shows an interaction that is dependent on the ratio of each fiber type.
... Moreover, because of the requirement of expensive detectors and a laser source, all laser diffraction analyzers are relatively expensive. These shortcomings are partially solved in dynamic image analysis (DIA) [31][32][33][34]. It is usually based on analyzing images of particles that have been separated using the free-fall method. ...
This study examines the potential of near-infrared hyperspectral imaging for assessing the size of polymer particles in model fractions based on the scattering phenomena. Different fractions of ground polymers, either methacrylate or polypropylene, were characterized by near-infrared spectra collected between 900 and 1700 nm. The possibility to estimate the size of polymer particles using hyperspectral images was confronted with a basic single spot near-infrared measurement. Hyperspectral imaging, in addition to the standard spectral data dimension, provides information about the spatial distribution of sample components and reveals changes in physical properties. Therefore, one can gain a better insight into the scattering phenomena and study the physical inhomogeneity of a sample in terms of particle size distribution. The partial least-squares models constructed to estimate particle size of polymers that were characterized by hyperspectral images (a pixel-based approach) outperforms models built for mean spectra regardless of the considered powdered polymer.
... One is a loss of molecular mass of the polymer; this issue will be considered more closely when discussing the recyclability of biopolymers and their composites. Another harm is the mechanical breakage of cellulosic reinforcement material (Teuber et al. 2016). As a strategy to avoid such adverse effects of high temperatures and shear stress, many studies have been carried out by dissolving the plastic in a solvent, followed by casting and evaporation (Arias et al 2015). ...
Society’s wish list for future packaging systems is placing some daunting challenges upon researchers: In addition to protecting contents during storage and shipping, the material must not bio-accumulate, and it should be readily recyclable by using practical processing steps. This article considers strategies employing bio-based plastics and reviews published information relative to their performance. Though bioplastics such as poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB) can be prepared from plant materials, their default properties are generally inferior to those of popular synthetic plastics. In addition, some bioplastics are not easily decomposed in soil or seawater, and the polymers can undergo chemical breakdown during recycling. This review considers strategies to overcome such challenges, including the use of biodegradable cellulose-based reinforcing particles. In addition to contributing to strength, the cellulose can swell the bioplastic, allowing enzymatic attack. The rate-controlling step in bioplastic degradation also can be abiotic, i.e. not involving enzymes. Though there is much more work to be done, much progress has been achieved in formulating bioplastic composites that are biodegradable, recyclable, and higher in strength compared to the neat polymer. Emphasis in this review is placed on PLA and PHB, but not to the exclusion of other bioplastic matrix materials.
... The fiber dimensions are generally characterized by 3D-microtomography [107,108] or by 2D image analysis after dissolution of the matrix. Different techniques may be employed, which are more or less accurate depending on the case considered [109][110][111]. Usually, size distributions of length L, diameter D and aspect ratio L/D are measured over a population of at least a few hundred fibers, and average values are derived from these distributions. ...
This chapter is devoted to natural fiber reinforced thermoplastic composites. First, the various fibers used to prepare thermoplastic-based composites and their main properties are presented and analyzed. The problems to solve (fibers degradation, compatibility with the matrix) are discussed. Then, the methods of preparation of natural fiber-based composites are introduced. As it is the topic of Chapter 2, we focus mainly on the melt compounding by twin-screw extrusion and its specific difficulties: dispersion of the fibers, breakage mechanisms, and thermal degradation. Finally, an overview of the main properties of the natural fiber-based composites is included.
... 4 described, the morphology of the wood components is not constant. It is susceptible to changes due to shear forces and high temperatures occurring during WPC processing [19]. Wood fibres provide a reinforcement characterised by high mechanical strength and a favourable shape factor. ...
Nowadays, the aim is to minimize the impact of a product or service on the environment in all phases of its life cycle. In particular, this applies to those in which the impact is greatest. One of the techniques that allow comprehensive assessment of the environmental impact of manufactured products is Life Cycle Assessment (LCA). With this method, an environmental declaration is made for the products obtained. WPC composites can be made in a sustainable way, without wasting any material and without altering. WPC composites can be made in a sustainable way, without wasting any material and without altering. Composites with wood fillers may be competitive to materials with inorganic fillers. Wood-polymer composites can be produced from original natural raw materials. They can also be obtained as a result of recycling, where either wood or polymers come from the recyclate. It is also possible to use both components from recovery. Another way is to use WPC as a future raw material. Research on the utilization of waste from such materials is also conducted in a number of research centres, taking material recycling as the basic direction, and technical products are manufactured from the obtained recyclate.
... For dynamic image analysis, particles flow in front of a recording camera that captures their shadows at a wanted frequency and that are then automatically analysed in a similar manner as static image analysis. Furthermore, the use of automatic systems allows to gain time and the number of analysed particles can rise up to several tens of thousands of objects in less than one minute [12] , such as with the QICPIC [13] , or with the MorFi Compact R ○ fibre analyser, which is a specific automatic equipment initially developed for the paper industry before or after a process stage that has been used in different studies [ 6 , 14-16 ]. The fibres circulate in a water or ethanol bath and image acquisitions allow for lengths of several mm to be analysed, but the relatively low camera resolution is penalising for single fibre diameter measurements. ...
The use of biomass in injection moulded or extruded thermoplastic composites is an important issue, especially when trying to add value to low-cost co-products. The objective of this work was to conduct a complete study on the morphological characterisation and carbohydrate analysis of a range of co-products obtained during the processing of flax straw. Thus, the morphology of (i) cut flax fibres, (ii) fragmented shives, and (iii) scutching and carding dusts is characterised using a dynamic image analyser with a sieving approach. These different fractions are then used to produce injection moulded composite materials. Their mechanical performances are discussed in relation to the morphology of the reinforcements, as well as their carbohydrate compositions and fine particle contents. Co-products, based on their reinforcement properties, can be classified into three categories. In all cases, a reinforcing effect is demonstrated for the tensile Young's modulus with an increase from +24 to +137% depending of the material. A linear relationship was observed between the cellulose content of reinforcing material and the tensile strength at break of the injection moulded composites. The results are promising for adding value to all flax co-products in plastics processing, targeting industrial applications in line with their intrinsic performances.
... The fiber dimensions are generally characterized by 3D-microtomography [107,108] or by 2D image analysis after dissolution of the matrix. Different techniques may be employed, which are more or less accurate depending on the case considered [109][110][111]. Usually, size distributions of length L, diameter D and aspect ratio L/D are measured over a population of at least a few hundred fibers, and average values are derived from these distributions. ...
Starch is one of the most common polysaccharides from natural and renewable resources. It is increasingly used in place of synthetic polymers for industrial applications and can be chemically modified to obtain products having specific properties. For example, cationic starches are largely used in the paper industry. They are generally prepared using conventional batch reactors, but they can also be obtained using reactive extrusion. In this chapter, after a brief introduction to the twin-screw reactive extrusion process, experimental results of starch cationization are presented. Then, a model based on flow simulation coupled to a kinetic equation is developed, allowing a clear understanding of the influence of the processing parameters on the extent of the cationization reaction. This model, experimentally validated, is then used to solve optimization and scale-up problems.
... Wood particles have dimensions that are approximately equal in all the directions and can have any shape [9]; then, they act as fillers. However, the initial morphology of the constituents of wood is not constant and is susceptible to changes resulting from the action of shear forces and high temperatures during the WPC processing [10]. Wood fibres provide reinforcement that is characterised by high mechanical strength as well as an advantageous shape factor. ...
Along with the growing consumption of wooden and wood-based products, the amount of waste generated during both production and consumption of these products increases. These wastes constitute a rich raw material base, the appropriate use of which can significantly reduce the use of natural wood raw material. Unfortunately, a significant proportion of them, especially of post-use and wood-based origin, end up in landfills. It seems necessary to find ways to use the generated waste. One of them is to use them in the form of strengthening polymer-wood composites. Composites with a wood filler can be a competitive product for materials with an inorganic filler. The wood filler is characterized by lower cost, higher availability and definitely lower density than glass fibers. An additional advantage of composites with wood fiber is their easy recycling and a smaller amount of waste products remaining after combustion. The use of a polymer matrix provides flexibility to the composite and has a positive effect on the ability of the material to stretch under the influence of temperature. The main advantage of the matrix in the form of a polymer is also to provide the product with resistance to the effects of the external environment, especially moisture and water. The main centers for the production of polymeric and wood composites are North America and Europe. Mainly floor, wall and roof platings are created. In addition, they are used as fences, windows and doors as well as additional equipment for platforms, landscape architecture, floor materials and panels
... However, the injection molding causes only a minor additionally reduction in fiber length. In line with Puglia et al. (2008) and Teuber et al. (2016a), fiber length reduction is increasing with increasing fiber content during compounding. With increasing fiber content the chance of higher interactions between the fibers increases. ...
Thermomechanical wood fibers, as usually used for medium density fiberboard or cardboard production, feature promising characteristics, like a high aspect ratio, for the utilization in thermoplastic composites. The present study investigates the influence of fiber loading and fiber geometry on the mechanical properties of wood-polypropylene composites in order to confirm the results that were found in a previously published literature review. Composites were compounded at fiber contents from 20 to 60 wt.%, using a co-rotating twin-screw extruder and subsequently injection molded to test specimens. Field emission scanning electron microscopy was carried out to evaluate the fracture morphology of the composites. Fiber length was evaluated using an applying a dynamic image analysis system. Compounding reduced fiber lengths up to 97%. The mechanical properties decreased with increasing fiber content for composites without a coupling agent. Strength properties peaking at a fiber content of 50 wt.% for composites containing MAPP. Tensile strength and flexural strength reached 48.1 and 76.4 MPa, respectively. However, it was found that the processing of these fibers into conventional compounding equipment is still challenging.
... About 150,000 fibers were measured for each sample. It was evaluated using the parameter LEFI, which is defined as the shortest way between the most distant endpoints of a fiber [28]. Images were taken with a frame rate of 175 Hz and a resolution of 4.2 MP using an M4 magnification, which results in a pixel size of 4.2 µm. ...
Composites with two types of reinforcement fibers open a large field of opportunities and combine properties. Glass fibers lead to higher strength and modulus, but they provide a brittle character. In contrast to this, man-made cellulose fiber composites show higher energy absorption and higher elongation-at-break. The aim of this study is to investigate the synergy of those two fiber types in a hybrid compound. Compounds with an overall fiber content of 16 vol% and different ratios of glass and man-made cellulose fibers were prepared with a twin-screw extruder and injection molded to test specimen. Mechanical properties as well as the composite morphology were studied for compounds with selective fiber-matrix-adhesion and without a coupling agent. A bimodal fiber length distribution was found in the hybrid compounds due to the different shortened fiber types. The long man-made cellulose fibers increase the impact strength and influences the fiber orientation in the hybrid.
... For the dynamic image analysis, a small piece of the injection molded specimen was cut out. Subsequently, the matrix of the composites was dissolved by boiling xylene in an experimental setup based on the Soxhlet extraction, which is a standard method to dissolve natural fibers from a PP matrix [40]. Isopropanol was used as carrier medium in which the dissolved fibers were added to the wet dispersion unit. ...
This paper focuses on the energetic evaluation of the single fiber pull-out test (SFPT) using regenerated cellulose fibers (RCF) in a PP matrix with a varying MAPP content. Glass fibers were used for reference purposes. By means of the SFPT the interfacial shear strength (IFFS), the critical fiber length (lc), the consumed energy of a fiber pull-out and the consumed energy of a fiber rupture were determined. Results were related to the fiber length distribution in injection molded specimens. It was shown that theoretically more fiber ruptures appear in composites with RCF than with GF. But RCF composites offer a larger number of long fibers, slightly underneath the critical fiber length, consuming a high amount of energy by being pulled out at a composite failure. The consumed energy of a fiber pull-out per length was increased by using MAPP but simultaneously the critical fiber length was significantly reduced.
https://authors.elsevier.com/a/1W2X6,UwqXFeIo
... To form the surface layer the wood flour of grades 180 and 1250 was used as the wood material, polypropylene of grade 1500J and polyethylene of grades 4223 T were used as the binder [19]. ...
The article describes a new multilayer wood-polymer composite material, the outer layer of which comprises wood flour, polypropylene, polybutadiene, concentrated dye. The inner layer comprises longwise oriented wood particles of the fibrous type of 2-10 mm and the recycled thermoplastic polymer. An experimental complex used to identify structural and operational characteristics of the composite material was presented. The experimental study of the mechanical properties of the product hardness, abrasion, cross-breaking strength were conducted. The results of the tests selected and validated the composite structure.
... Wood polymer composite (WPC) has become a promising material in recent years because of its numerous advantages like easy processing, productivity, low density, high specific strength, easy availability and cost effectiveness (Liu et al. 2016;Ashori 2008;Saheb and Jog 1999;Hazarika and Maji 2014;Teuber et al. 2016). Being a green material, easy availability and low cost, the use of WPC has been increasing day by day (Liu et al. 2016). ...
Citric acid was used as the cross-linker to prepare the sustainable wood starch nanocomposites (WSNC) from the renewable resources like starch and soft wood flour using water as the solvent. Nano SiO2 was employed to develop the physicochemical properties of the WSNC via a green path. In this process, starch was grafted with methylmethacrylate (MMA) and SiO2 was modified with N-cetyl-N,N,N-trimethyl ammonium bromide. Three different percentage of modified nano SiO2 (1–5 phr) were employed in the preparation of the composites and their properties were characterized by Fourier transform infrared spectroscopy. The morphological features of the composites were investigated through transmission electron microscopy and scanning electron microscopy study. Mechanical and dynamic mechanical properties like storage modulus, loss factors and tan δ value of the composites were thoroughly investigated. Thermal stability, water resistance and flammability of the composites were significantly improved after incorporation of modified SiO2. The maximum improvements in properties were achieved containing 3 phr modified SiO2 composites.
... A study led on wood polymer composites demonstrated the inuence of process parameters (e.g., screw design, temperature, RPM) on the size of the particles in the nal material. 87 As reported by Hanawalt, 88 the temperature of the process should be set in accordance with the thermal stability of the ber in order to prevent thermal degradation. Such degradations would certainly cause some aws into the ber bundles and decrease the mechanical properties. ...
Natural fiber composites have various applications, since they can bring interesting mechanical and sustainability properties. Extrusion with single- or twin-screw is the main industrial process to incorporate lignocellulosic fibers into polymers. In this review, origin and preparation of lignocellulosic fibers are first discussed, before discussing the composite processing, with a particular emphasis on the impact of process conditions on the composites final properties which is highly related to the final application. A broad panel of composites reinforced with lignocellulosic fibers is reviewed along with their polymeric matrix, lignocellulosic fiber type and pretreatments, extrusion process conditions. Finally, the most critical extrusion process parameters (screw profile, speed and temperature) are also examined in order to determine some guidelines to optimize lignocellulosic fiber composites preparation.
... The objective M7 with a resolution of 4.2 mm was employed, that realizes a minimal fiber size of 12.6 mm and a maximum fiber size of 8.66 mm. The distribution of the calculated fiber lengths is length based (q1), which is well-suited for representing broad ranges of size distributions [24]. The values of the mean, the median, the 10th and the 90th percentile were analyzed to acquire information about the scope of the distribution. ...
This investigation focuses on the fracture toughness of injection molded compact tension (CT) specimen of man-made cellulose fibers reinforced composites with PP as their matrix and different varying fiber contents. The influence of the fiber orientation and the addition of a coupling agent on the fracture toughness was determined using an optical strain measurement and a micro computer tomography. It was verified that a reinforcement with man-made cellulose fibers leads to significantly higher values of fracture toughness and J-Integral in comparison to glass fiber reinforcement. Furthermore, it was demonstrated that the majority of fibers in the CT specimen show an orientation perpendicular to the flow direction of the injection molding process. Thus, a notch direction parallel to the flow direction leads to significantly higher values. This is a result of less local strains around the crack path, as well as of a higher amount of fiber pull-outs in the fractured surface. The coupling agent MAPP creates stronger fiber-matrix adhesion, which results in increasing values of the fracture toughness but a decreasing of the J-Integral values due to less fiber pull-outs.
Issu d’une agriculture française, le lin a de véritables atouts pour une utilisation comme renfort de matériaux composites, tels que les excellentes propriétés mécaniques spécifiques de ses fibres (tissu de soutien) et de nombreux co-produits dont les anas (tissus de conduction). Les anas représentent plus de 50 % de la biomasse produite suite au teillage dont la diversification de ses utilisations est une réelle problématique pour les teilleurs. L’approfondissement des connaissances sur les anas de lin est l’objet de la première partie, depuis leur origine comme tissu du xylème au sein des tiges de lin et jusqu’au renforcement de matériaux composites. Une étude microstructurale et des propriétés mécaniques des cellules du xylème de lin est menée, accompagnée de la caractérisation (granulométrique, biochimique, etc.) des anas suite à différents modes de broyage et comparativement à des poussières issues du teillage. Les propriétés mécaniques des composites injectés subséquemment réalisés sont ensuite analysées. Les conséquences des étapes de mise en œuvre sur la granulométrie des anas, la nature des co-produits ou encore des matrices thermoplastiques sont étudiées dans l’objectif de comprendre les mécanismes de renforcement des anas de lin. En deuxième partie, deux verrous sont analysés à l’échelle de la fibre unitaire : l’impact des conditions hygroscopiques sur l’organisation interne des microfibrilles de cellulose lors d’essais de traction par des mesures de diffraction aux rayons X (synchrotron Soleil), et enfin, les conséquences d’une maladie vasculaire, la verticilliose, sont étudiées sur les propriétés mécaniques des fibres et des parois végétales de lin.
Whatever in pulp or biocomposite sectors, the elements called fines coming from plant fibres have generally a length lesser than 200 μm. Their mechanical impact has long been debated in short plant fibre thermoplastic composites. Are they solely a filling agent or on the contrary, have they a potential of reinforcement in such composites depending on their numbers, their length and aspect ratio? This work proposes an original experimental approach to explore the mechanical role of fine flax particles. Based on controlled milling of an initially homogeneous flax fibre batch that provides a population of fines (99% under 200 μm, average Lw of 147 μm), we devised a set of composites made of an increasing content of flax fines (0, 3.1, 5.6, 12.3, 20.4, 34.6 and 40.2%-vol) mixed with poly(propylene) (PP) and maleic anhydrid grafted PP (PP-PPgMA). Reference composites reinforced with chalk and also with cut flax fibre (Lw of 2000 μm) were also manufactured and studied. Results demonstrate that, despite a low aspect ratio (5 ± 0.2 for 20.4%-vol), fines can act more than as just a simple filler, a slight modulus reinforcement is depicted but only beyond a high threshold of about 20%-vol (+29% compared to raw PP for 20.4%-vol). In addition to PP, we then investigated the mechanical influence of the flax fines in two representative matrix thermoplastic families Poly(amide)-11 (PA11) and poly(butylene-succinate) (PBS). We highlighted an increase of the Young’s modulus of PA11 and PBS fines composites (+41% and +115, respectively for 20.4%-vol), whereas strengths were lower compared to the respective neat polymers, exhibiting the possible negative role of fines on composite mechanical properties.
In this study, poly(lactic acid) (PLA)/wood flour (WF) composites were prepared by first blending PLA with organo-montmorillonite (OMMT) at different contents (0.5, 1, 1.5, and 2 wt %). The physical and mechanical properties of the virgin and OMMT modified PLA and its WF composites were tested. The results showed that: (1) at low OMMT content (<1 wt %), OMMT can uniformly disperse into the PLA matrix with highly exfoliated structures. When the content increased to 1.5 wt %, some aggregations occurred; (2) after a second extruding process, the aggregated OMMT redistributed into PLA and part of OMMT even penetrated into the WF cell wall. However, at the highest OMMT content (2 wt %), aggregates still existed; (3) the highly exfoliated OMMT was beneficial to the physical and mechanical properties of PLA and the WF composites. The optimal group of OMMT-modified PLA was found at an OMMT content of 0.5 wt %, while for the PLA/WF system, the best properties were achieved at an OMMT content of 1.5 wt %.
The particle size and shape are of momentous significance for the mechanical properties of plastic composites. However, natural fillers, like wood, are not consistent in these attributes. In order to investigate the shared traits between these characteristics, WPCs were produced using polypropylene, hardwood and softwood fillers with different particle sizes and a coupling agent. Afterwards, specimens were processed using an injection molding machine. The filler sizes and shapes were measured using dynamic image analysis. Furthermore, a shortening of coarser particles was detected. Mechanical tests were carried out to gain information about the tensile, flexural and Charpy impact properties. Neither very coarse nor very fine particles showed the best results. Instead, medium-sized particles proved to be the best option. The evaluation of the particle geometry verified a definite correlation between the shape and the mechanical properties, especially regarding the convexity, which can be a useful indicator of the quality of fiber-matrix interaction. The fiber orientation in the matrix was visualized with images taken by X-ray micro tomography.
Current requests in the field of food packaging lead to the reasoned design of materials able to improve the global environmental balance of the food/packaging system by minimizing the negative environmental impact of the packaging material while improving its positive role in the food wastes and losses reduction that strongly impact our environment. This means to simultaneously control food degradation reactions while limiting undesirable migrations of additives from packaging towards in respect of our health and remaining economically competitive. The substitution of oil-based materials by ones issued from renewable and non-food resources (e.g. issued from bioconversion of agro-food wastes, for example) and furthermore, fully biodegradable in natural conditions is also a necessity and represents a significant breakthrough from the research in the field of food packaging. In this context, increasing attention is given to full-biocomposites, i.e. composite materials based on constituents all biosourced and biodegradable. Developing full-biocomposites for food packaging requires taken into account numerous factors, and this is even more important for complex biodegradable materials due to the gap in knowledge on their behaviour and potentialities in usage conditions. The objective of this chapter is to decipher the state of the art on full-biocomposites by considering the specific stakes relative to the food packaging application. After the first part of introduction, the second part will present the role of packaging to ensure food quality and safety and how it should be designed in such a way to reduce food waste and losses. The third part will present the window of mass transfer properties of full-biocomposites, which is the main functional property when considering the food packaging application. The fourth part will consider the economical competitiveness of full-biocomposites, the fifth part will treat the safety issues and the sixth of the different options of end of life and waste management.
This paper presents results from sieve analysis and image analysis-based particle size measurement (FibreCube) of wood particles for the manufacture of wood-plastic composites. Wood of different origin (virgin Norway spruce, post-industrial particleboard residues, mixed waste wood) was used for particle manufacture. It was found that size distributions were different, although milling conditions were equal.
This work describes a systematic study of the compounding conditions by twin-screw extrusion on the defibrization process that modulates the fiber aspect ratio and in turn the mechanical properties. Composites made of polycaprolactone reinforced by 20% hemp fibers were prepared by melt blending. The influence of the extrusion parameters (screw speed, feed rate, barrel temperature, and screw profile) and the initial fiber moisture content on both the fiber dimensions and the mechanical performance of the composite was investigated. The fiber aspect ratio increased when the fibers were water plasticized, principally at a higher feed rate and under a moder-ated extrusion temperature. The screw speed slightly influenced the fiber dimensions. Flow modeling was used to estimate the specific mechanical energy provided to the fibers, which ranged from 300 to 1700 kWh/t. Independent of the screw profile, a decrease in fiber length with an increase in energy was observed. The evolution of the fiber length and aspect ratios with respect to energy can be accu-rately described by an exponential function. V C
The compounding of recycled polypropylene (RPP) and wood saw dust (WSD) are carried out using five different filler loadings (0, 10, 20, 30, 40, and 50%) with three WSD filler sizes (100, 212, and 300 mm). The composites are mixed and extruded using Haake Rheodrive 500 twin screw extruder. The mechanical and water absorption properties of composites are characterized accordingly. The results show that composites with a smaller particle size (100 mm) have remarkably higher properties compared to others (212 and 300 mm). Composites filled up to 30% WSD exhibits improved mechanical properties but the value dramatically decreased above 30% filler loading. The evidence of fiber-matrix interphase is analyzed using scanning electron microscope (SEM).
In this study the influence of filler particle size (40, 50, and 60 meshes) and coupling agent concentration (0 and 2 wt%) on the composite mechanical properties were studied. Specimens having 30 wt% wood flour of poplar were mixed with polypropylene and polypropylene grafted maleic anhydride (PP-g-MA) as coupling agent. It was found that strength properties of the composites can be improved moderately by adding 2 wt% PP-g-MA. It was also observed that smaller filler particles provide higher tensile modulus than the larger sized filler. Moreover, increase in aspect ratio of the wood particles contributed to the enhancement in the mechanical properties of the composites. The elongation value was not found to have any considerable variation with particle size. The PP-wood flour composites exhibited low impact strength compared to pure PP. In general, Wood flour could be considered as a potential source of low cost, natural fibers for composites.
During the processing of fibre-reinforced thermoplastics, such as in extrusion and injection moulding, fibre breakage takes place and the average fibre length is reduced. This reduction in length might result in a loss of reinforcement efficiency because the mechanical properties of the composite strongly depend on residual fibre length. For this reason an accurate measure of the fibre length obtained at different process conditions is necessary to relate it with the process parameters. The most used method for determining a fibre length distribution is performed measuring the fibre length by image analysis from micrographs. In the case of thermoplastics reinforced with long fibres, the inability to measure the longer fibres may lead to an underestimation of the average fibre length and thus the correlation between the process parameters and the fibre damage is impaired. In this paper a new procedure is proposed, based on template matching and image mosaic, allowing the measure of fibres of any size. Furthermore this technique allows a researcher to consider all the fibre contained within the specimen. The results obtained with this new procedure is a more accurate estimation of the average fibre length and its distribution even with fibres longer than the available sizes of the micrographs.
Wood-polyvinyl chloride (PVC) composites were prepared using industrial wood particles used for manufacturing three-layer
particleboards. The effect of particle size (0.25–0.5, 0.5–1, 1–2, and 2–4 mm) on the mechanical properties of the composites
was investigated. The effect of cross-section size (4×10, 6×15 and 8×20 mm2) of composite pieces made by an injection moulding method was also studied. Both the particle size and specimen cross-section
area significantly influenced these properties. The tensile and flexural properties as well as the impact strength in general
increased with increasing particle size, and decreased with increasing cross-section size.
In the present study, Polyamide 12 was compounded with glass fibers in both laboratory and industrial twin screw extruders using various processing conditions (screw speed and feed rate). Dead-stop experiments were performed and samples were collected at different locations along the screws in order to determine the fiber length distribution and the extent of fiber breakage. Results show that significant fiber break-up occurs right after the addition of glass fibers to the molten matrix. Similarly fiber length distribution changes drastically at the first sampling location, near the glass fiber feeder. Processing conditions also influence the extent of degradation: it increases with screw speed and decreases with feed rate, which controls the residence time. Flow modelling has been used to calculate the flow conditions along the screw profile. It is shown that the modified Shon-Liu-White model previously proposed to describe the average fiber length evolution as function of specific energy is not able to correctly predict the evolution along the screw profile. In similar processing conditions, the large industrial extruder appears as less severe than the small laboratory one.
Fiber length and distribution play important roles in the processing and mechanical performance of fiber-based products such as paper and fiberboard. In the case of wood–plastic composites (WPC), the production of WPC with long fibers has been neglected, because they are difficult to handle with current production equipment. This study provides a better understanding of the effect of fiber length on WPC processing and properties. The objectives of this study were therefore to determine the role of fiber length in the formation process and property development of WPC. Three chemithermomechanical pulps (CTMP) with different lengths, distributions, and length-to-diameter ratios (L/D) were obtained by mechanical refining. Length, shape, and distribution were characterized using a fiber quality analyzer (FQA). The rheometer torque properties of high-density polyethylene (HDPE) filled with the pulps at different loads were studied. Variations in fiber load and length distribution resulted in significant variations in melting properties and torque characteristics. Composites from the three length distributions were successfully processed using extrusion. Physical and mechanical properties of the obtained composites varied with both length distribution and additive type. Mechanical properties increased with increasing fiber length, whereas performance in water immersion tests decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
We consider the scattering of light by single wood fibers both theoretically and experimentally. We describe the size and the shape distributions and the internal structure and chemical composition of the wood fibers. We have modeled the random shape of the hollow, cylindrical wood fiber by using multivariate lognormal statistics. We have computed wood-fiber absorption and scattering cross sections, asymmetry parameters, and scattering phase matrices in the ray-optics approximation. Finally, we have provided experimental results from angular scattering measurements for wood fibers and present what we believe is the first comparison between these measurements and ray-optics computations for Gaussian random wood-fiber models. In spite of the complicated internal structure of the wood fiber, our model together with the ray-optics treatment explains the scattering measurements surprisingly well.
The size distribution of wood fibres or particles as raw materials for fibreboards or particleboards is an important parameter for the production control which is currently measured using simple means such as sieve analysis. Today, automatic image processing methods for laboratory and on-line measurements are available which can be adapted to the material type. Shape measurements for separated particles together with weighted size distributions provide more detailed information than sieve analysis: E. g. the different lengths of particles from various wood species which originate from the same sieve fraction; the amount of shives and fibre bundles in MDF fibre material corresponding to the gap size in the refiner; different components (e. g. particles and fibres) in particle mixtures. The FibreShape system operated at Fraunhofer-Institut für Holzforschung Wilhelm-Klauditz-Institut (WKI) is a helpful tool for these investigations. In addition, using specific image processing procedures which were developed at WKI, it is also possible to recover and measure particle shapes in mat and board surfaces for a continuous monitoring of particle geometry in the production.
Commercial wood flour, the most common wood-derived filler for thermoplastics, is produced in a mixture of particle sizes and generally has a lower aspect ratio than wood and other natural fibers. To understand how wood flour and fiber characteristics influence the mechanical properties of polypropylene composites, we first investigated the effect of different sizes of wood flour particles on the mechanical properties of wood-flour-filled polypropylene composites. We then compared the properties of wood-flour-filled composites to those of composites reinforced with refined wood fiber. We also studied the effect of a maleated polypropylene coupling agent on composite properties. Wood flour particles (35, 70, 120, and 235 mesh) were compounded at 40% by weight with polypropylene. Increases in tensile and flexural strength and modulus of the wood flour composites were found to correspond with increases in aspect ratio. Notched impact energy increased with increasing particle size, whereas unnotched impact energy decreased with increasing particle size. Refined wood fiber and 40-mesh wood flour was compounded at 20% and 40% by weight with polypropylene. Wood fiber resulted in higher strengths at both filler levels and higher moduli at the 40% level compared to the strength properties of wood flour composites. The higher aspect ratio of the wood fiber had little effect on impact energy. The maleated polypropylene coupling agent caused greater strength increases in wood fiber composites than in wood flour composites. The coupling agent did not significantly affect tensile or flexural moduli. Our results clearly support the use of higher aspect ratio wood fibers and coupling agents for increasing the strength of wood/plastic composites.
The fungal durability of woodfiber/thermoplastic composites is an area of recent scientific interest. Model composites containing 50 percent wood, on an ovendry composite weight basis, were produced using a range of wood particle sizes from two different wood species. The decay resistance of the composites was evaluated against Gloeophyllum trabeum and Trametes versicolor. It was found that weight loss increased as the wood particle size increased. Decay in the pine-based composites was more sensitive to particle size than the maple-based composites. More wood volume is accessible to the fungi on the faces and along the edges of composites produced with large particles, resulting in higher weight losses. In addition to the exposure of greater wood volume when large particles are used, forces induced by moisture absorption and swelling may act to increase the accessibility of the wood in these composites.
Wood pallets and shipping crates represent a large source of raw material available for use in value-added composites. To determine the feasibility of using wood fibers derived from pallets in wood-plastic composites, this study compared the mechanical properties of polypropylene (PP) composites combined with either wood flour or wood fiber. Wood flour is the most common wood-derived filler used in the plastics industry. Moving from a particulate filler like wood flour to a reinforcing fiber results in property enhancements. In this study, the use of fiber derived from wood pallets and shipping crates as a filler for PP resulted in tensile and flexural strength improvements compared with wood-flour-filled PP. The addition of stearic acid to these composites to increase dispersion of the wood filler in the PP did not improve properties: however, the addition of maleated PP to improve the interfacial adhesion between the two phases resulted in strength improvements.
Extrusion compounding and injection molding processes are frequently employed to fabricate short-fiber-reinforced polymers. During extrusion compounding and injection molding processing, considerable shear-induced fiber breakage takes place and results in a fiber length distribution (FLD) in final short-fiber-reinforced polymer (SFRP) composites. Also, during compounding and molding processing, progressive and continuous changes in fiber orientation occur and lead to a fiber orientation distribution (FOD) in final composites. Both FLD and FOD are governed by a number of design and fabrication factors including original fiber length, fiber content, mold geometry and processing conditions. The mechanical properties such as strength, stiffness and fracture toughness or specific work of fracture (WOF) of SFRP composites have been shown to depend critically on FLD and FOD. The present paper reviews previous research work on the effects of design/fabrication factors on FLD and FOD and the effects of FLD and FOD on the strength, stiffness and toughness or WOF of SFRP composites. Conclusions which can be drawn from the literature are presented with discussions of areas in which further research is required.
Thermo-mechanical pulp (TMP) fibres made from beech wood were produced using increasing refiner gap widths and thus with increasing fibre length and coarseness. Fibres (60% by weight) were compounded in an internal kneading mixer using high-density polyethylene as the matrix and injection-moulded. Fibre lengths and length/width ratios were determined a) before processing and b) after injection-moulding and Soxhlet extraction using the optical FibreShape system. An increase in fibre length resulted in a decrease in water absorption and an improvement in flexural strength and modulus of elasticity of the wood-plastic composites (WPC). However, flexural strength of the WPC with TMP fibres was not improved compared to WPC with wood flour when maleic anhydride-grafted polyethylene (MAPE) was used as a coupling agent. After injection-moulding, differences in length of the various TMP fibre types were minor. Fibre geometry before processing strongly influences the water absorption and flexural properties of the composite. Fibre treatment with emulsified methylene diphenyl diisocyanate (EMDI) resin before compounding was shown to be equally efficient in reducing water absorption and improving flexural strength as the addition of MAPE during the compounding step.
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.
Natural fibres from miscanthus and bamboo were added to poly(lactic acid) by twin-screw extrusion. The influence of extruder screw speed and of total feeding rate was studied first on fibre morphology and then on mechanical and thermal properties of injected biocomposites. Increasing the screw speed from 100 to 300 rpm such as increasing the feeding rate in the same time up to 40 kg/h helped to preserve fibre length. Indeed, if shear rate was increased with higher screw speeds, residence time in the extruder and blend viscosity were reduced. However, such conditions doubled electrical energy spent by produced matter weight without significant effect on material properties.The comparison of four bamboo grades with various fibre sizes enlightened that fibre breakages were more consequent when longer fibres were added in the extruder. Longer fibres were beneficial for material mechanical properties by increasing flexural strength, while short fibres restrained material deformation under heat by promoting crystallinity and hindering more chain mobility.
Wood–plastic composite (WPC) is an environmentally progress way of combining recycled plastics and wood flour. The composite typically consists of four major elements: wood flour, thermoplastic plastics, coupling agent, and lubricant. The physical and mechanical properties of WPCs highly depend on the material formulation, and the optimal material composition is an essential topic of current research. This study investigated the effects of changing material compositions on the physical and mechanical properties of WPCs. The studied WPCs were extruded molding WPCs manufactured using recycled polypropylene (RPP) plastics and wood flour. The study evaluated four parameters: (1) wood flour particle size; (2) coupling agent dosage; (3) lubricant content; and (4) the mass ratio of wood and RPPs. The results showed that using finer wood flour (smaller than 125μm) can improve the tensile and flexural strength of WPCs, and reduce the swelling due to water adsorption. The optimal concentration of the coupling agent (Maleic Anhydride Polypropylene) and lubricant (Zinc stearate) in WPCs were both 3%. Adding the proper amount of coupling agent can improve the mechanical properties and significantly reduce the swelling, but over-dosing the lubricant significantly increased swelling and reduced all the mechanical properties of the WPCs. Maintaining wood content at 50% or less produced the best mechanical properties, and wood content above approximately 50% resulted in reduction of all physical and mechanical properties of WPCs. The study demonstrated the relationship between moisture adsorption to thickness swelling. Reducing thickness swelling from water adsorption, or reducing the exposure of wood fibers to atmosphere, may also improve all the mechanical performances of WPCs.
The final properties of composite materials are highly dependent on the residual geomet-rical parameters (length, diameter, aspect ratio), orientation and distribution of the fibres in the matrix, which in turn are related to the processing conditions. This study analysed the fibre structure variation during the processing of a polypropylene matrix reinforced with cellulose flax pulp for different rein-forcement concentrations. The fibre's geometrical parameters, length, diameter and aspect ratio have been measured and their statistical distributions have been assessed for each concentration. Further-more, the effect of the microstructure variation on the final mechanical properties was analysed. In particular, changes in the interfacial area were evaluated based on the hypothesis that the fibres were cylindrical in shape and considering the average values of the diameters and the lengths calculated us-ing a statistical distribution approach. The fibre interfacial area after the process decreases as the fibre concentration increases and this evaluation explains how the adhesion methods that are used for fibre surface modification fail because of the decrement in the modifier interfacial density. The Halpin–Tsai approach was used to model the experimental data obtained from tensile tests for different composites, so as to confirm the effect of fibre parameters, such as aspect ratio and interfacial area values, in the PP/cellulose blends final properties.
The inter-relationship between processing conditions and fiber breakage has been studied for glass fiber-reinforcedpolyamide 12, prepared using (i) an internal batch mixer, (ii) a laboratory scale corotating twin screw extruder, and (iii) an industrial scale twin screw extruder. The average fiber lengths and fiber length distributions were measured for various compounding conditions (screw or rotor speed, mixing time, feed rate). Experimental results have shown that fiber breakage depends on both screw speed and mixing time, the later being controlled, in an extruder, by the feed rate. For a given compounding system (batch mixer or twin screw extruder), the energy input (specific mechanical energy, SME) during the compounding process is found to be a reliable parameter, which governs fiber length (average, minimal, and maximal) evolution. Experimental data are correctly described with a model defining change in fiber length as a function of SME. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
The effect of separation techniques of fibers and the use of coupling agent and processing methods of the composites on the size reduction of the fibers after processing them with polypropylene (PP) matrix was presented. Fiber length distribution (FLD), fiber width distribution (FWD), and fiber volume distribution (FVD) of wood and hemp fibers in the composite were characterized using X-ray microtomography. The results show that X-ray microtomography technique is a non-destructive and powerful technique to study the three dimensional structure of the composite materials without any sample preparation, which results some artefacts on the structure of the fibers. The use of MAH-PP coupling agent decreases the fiber breakage in the composite, and a small width distribution and higher aspect ratio are obtained for the carded and enzyme separated hemp fibers.
In this study, PVC/(wood flour) (WF) composites were prepared by using a counterrotating twin-screw extruder, and the effects on the mechanical properties of concentration and particle size of the WF, type and amount of coupling agent, K value of PVC, feed rate of extruder, and die temperature were investigated. Optimization of various formulation parameters based on the Taguchi method demonstrated that the wood content and wood particle size were the most important parameters. Flexural modulus increased upon increasing WF loading up to 50 wt%. Also, flexural strength and modulus increased with particle size because of the higher aspect ratio and better quality of mixing. Use of coupling agents had a minor effect that was attributed to the moderately high polarity of PVC causing relatively good compatibility between WF particles and the PVC matrix. The optimum level of WF calculated by considering the contribution factor was 50 wt%. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers
While editing the first issues of Particle Characterization it has been recognized by the editors that the papers submitted differ widely in the representation of data and in the nomenclature chosen to characterize such common variables as particle size, different equivalent particle diameters, average particle sizes, cumulative and density values of a distribution etc. In oder to make papers published in this Journal more readily assimilable and graphs representing particle size analysis data instantly recognizable by using agreed upon standardized nomenclature the following paper has been submitted by one of the editors. It was first presented at the Harold Heywood Memorial Symposium, September 1974, at the University of Technology, Loughborough, U. K.
This work aims at simulation by particle tracking the local residence time distributions (RTDs) of a co-rotating twin-screw extruder using computational fluid dynamics. Simulated results follow reasonably well the trend of experimental results obtained by an in-line measuring instrument for different screw configurations and feed rates. To analyze the distributive mixing performance and overall efficiency of different types of kneading discs (KDs), mixing parameters such as area stretch ratio, instantaneous efficiency, and time-average efficiency are calculated. Among KDs with stagger angles 45°, 60°, and 90°, the 90/10/64 with disc gaps is most efficient in terms of distributive mixing. The effects of the disc width and disc gap on the local RTD and distributive mixing are also discussed. This provides a numerical tool for assessing point-by-point information on the local RTD, flow, and mixing along the screw extruder. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
The mechanism of fiber length degradation during twin screw extrusion compounding and methods to reduce it through process and machine design are extremely important in discontinuous fiber reinforced composites. Fiber damage along the screw and the extruder die are determined for three screw designs with different mixing sections. The pellet quality, wet-out, and fiber dispersion in the extruded strands are compared. The fiber orientation distributions in the screw are determined to identify regions of higher fiber interaction. The fiber damage during subsequent injection molding has also been determined. The tensile, flexural, and impact properties of the tensile bars are compared. It is found that the residence time, fill-up, and the intesity of mixing during extrusion compounding have a predominant effect on fiber length degradation. The screw designs were seen to have a greater effect on the fiber damage in the 40 wt% glass-filled polymer than the 30 wt% glass-filled polymer. However, the mechanical properties of the 30 wt% glass-filled polymer showed an increasing trend compared to the 40 wt% glass filled polymer. A screw design that provides a balance of the fiber length, wet-out, and fiber dispersion was noted to give consistent mechanical properties.
Composites of wood in a thermoplastic matrix (wood–plastic composites) are considered a low maintenance solution to using wood in outdoor applications. Knowledge of moisture uptake and transport properties would be useful in estimating moisture-related effects such as fungal attack and loss of mechanical strength. Our objectives were to determine how material parameters and their interactions affect the moisture uptake and transport properties of injection-molded composites of wood-flour and polypropylene and to compare two different methods of measuring moisture uptake and transport. A two-level, full-factorial design was used to investigate the effects and interactions of wood-flour content, wood-flour particle size, coupling agent, and surface removal on moisture uptake and transport of the composites. Sorption and diffusion experiments were performed at 20°C and 65 or 85% relative humidity as well as in water, and diffusion coefficients were determined. The wood-flour content had the largest influence of all parameters on moisture uptake and transport properties. Many significant interactions between the variables were also found. The interaction between wood-flour content and surface treatment was often the largest. The diffusion coefficients derived from the diffusion experiments were different from those derived from the sorption experiments, suggesting that different mechanisms occur. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 752–763, 2007
The main goal of this research is to innovate wood-plastic composites by using various wood particle sizes and different mixture ratios (weight ratio) of HDPE. (High Density Polyethylene). After mixing the wood particles (recycled wood waste) and the plastic powder, we use a molding and pressing process to make composites with a thickness of 12 mm. By doing so, the wood particle content can be increased to 75%. This kind of composite provides excellent dimensional stability, its moisture content is under 2.5%, and the thickness swelling rate after 24 hr water absorption is under 7.5%. The maximum static bending strength of this composite reaches 20.7 N/mm(2), and is better than that of general commercial particleboards. The composite made of larger sized wood particles has better strength properties. In addition, when the plastic content ratio increases, the dimensional stability of the composite will increase as well. After the soaking process in boiling water, the static bending strength of wet composite remained at 50%; this shows the good weather resistance of the composite. The surface veneer overlaid peeling strength of the composite showed 1.02-1.63 N/mm. After the evaluation of processing, cost of material and strength properties of the composite, we would suggest that the use of 70% of wood particles and 30% of plastic powder is practical to produce proper sized composites.
Although wood/cellulose-plastic composites (WPC) of low wood/cellulose content have been more accepted worldwide and are promoted
as low-maintenance, high-durability building products, composites containing high wood/cellulose content are not yet developed
on an industrial scale. In this study, flow properties, mechanical properties, and water absorption properties of the compounds
of cellulose microfiber/polypropylene (PP) and maleic anhydride-grafted polypropylene (MAPP) were investigated to understand
effects of the high cellulose content and the dimensions of the cellulose microfiber. The molding processes studied included
compression, injection, and extrusion. It was found that fluidity is not only dependent on resin content but also on the dimension
of the filler; fluidity of the compound declined with increased fiber length with the same resin content. Dispersion of the
composite was monitored by charge-coupled device (CCD) microscope. Increasing the plastic content in the cellulose-plastic
formulation improved the strength of mold in addition to the bond development between resin and filler, and the tangle of
fibers. The processing mode affected the physicomechanical properties of the cellulosic plastic. Compression-molded samples
exhibited the lowest modulus of rupture (MOR) and modulus of elasticity (MOE) and the highest water absorption, while samples
that were injection-molded exhibited the highest MOR (70 MPa) and MOE (7 GPa) and low water absorption (2%).
The influence of processing parameters, e.g. throughput and temperature, of the compounding step of wood plastic composites was investigated in this work. The effects
on the mechanical properties as well as the influence on the colour of the produced composites were correlated with the different
processing parameters. The composites showed a wide range of good processability, only at high temperature and low throughput
strong darkening occurred, as well as a loss of tensile strength was found for these samples.
The structure–property relationship of wood flake–high-density polyethylene (HDPE) composites was studied in relation to the matrix agent melt flow behaviour and processing technique. The flake distribution and flake wetting were optimised to obtain acceptable mechanical properties in these composites using two processing techniques, namely twin-screw compounding and mechanical blending. The microstructure of the composites revealed that the twin-screw compounded composites based on medium melt flow index (MMFI) HDPE always achieved better flake wetting and distribution, and therefore had higher mechanical properties, than those mechanically blended composites or twin-screw compounded composites with low MFI (LMFI) HDPE. For 50:50 wt% composites the overall flake wetting, depending on processing technique and matrix flow behaviour, is ranked as compounded MMFI>compounded LMFI>blended MMFI>blended LMFI. However, the uniformity of flake distribution of the composites follows a somewhat different pattern, i.e. compounded MMFI>blended MMFI>compounded LMFI>blended LMFI. Evidence shows that the medium MFI HDPE penetrates into lumens of wood fibres in wood flakes. This phenomenon combined with flake wetting and flake distribution had a profound effect on the mechanical properties, in particular the impact strength.
Study characterized and analyzed form factor, elementary composition and particle size of wood dust, in order to understand its harmful health effects on carpenters in Quindío (Colombia). Once particle characteristics (size distributions, aerodynamic equivalent diameter (D(α)), elemental composition and shape factors) were analyzed, particles were then characterized via scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray analysis (EDXRA). SEM analysis of particulate matter showed: 1) cone-shaped particle ranged from 2.09 to 48.79 µm D(α); 2) rectangular prism-shaped particle from 2.47 to 72.9 µm D(α); 3) cylindrically-shaped particle from 2.5 to 48.79 µm D(α); and 4) spherically-shaped particle from 2.61 to 51.93 µm D(α). EDXRA reveals presence of chemical elements from paints and varnishes such as Ca, K, Na and Cr. SEM/EDXRA contributes in a significant manner to the morphological characterization of wood dust. It is obvious that the type of particles sampled is a complex function of shapes and sizes of particles. Thus, it is important to investigate the influence of particles characteristics, morphology, shapes and D(α) that may affect the health of carpenters in Quindío.
The aim of this study was to test the measurement precision and accuracy of the Kajaani FS-100 giving attention to possible machine error in the measurements. Fiber length of pine pulps produced using polysulfide, kraft, biokraft and soda methods were determined using both FS-100 and FiberLab automated fiber length analyzers. The measured length values were compared for both methods. The measurement precision and accuracy was tested by replicated measurements using rayon stable fibers. Measurements performed on pulp samples showed typical length distributions for both analyzers. Results obtained from Kajaani FS-100 and FiberLab showed a significant correlation. The shorter length measurement with FiberLab was found to be mainly due to the instrument calibration. The measurement repeatability tested for Kajaani FS-100 indicated that the measurements are precise.