Thermoplastic composties of polystyrene: Effect of different wood species on mechanical properties

Both softwood (spruce) and hardwood (aspen and birch) species in the form of different pulps (e.g., sawdust, chemithermomechanical pulp, explosion pulp and OPCO pulp) have been used (10–40 wt% composite) as reinforcing fillers for thermoplastic composites of polystyrene. Mechanical properties, are examined, e.g., tensile modulus, tensile strength at maximum point, and the corresponding elongation and energy as well as impact strength of compression molded composites. To improve the compatability of wood fibers which are hydrophilic and the polymer matrix which is hydrophobic, poly[methylene(polyphenyl isoeyanate)] (2 and 8 wt % of polymer) was used as a coupling agent. The mechanical properties of the treated composites are improved up to 30% in fiber content whereas a downward trend for untreated composites was observed when an increase in fiber content occurred. The overall improvements in mechanical properties due to the addition of isocyanate can be explained by the linkage of isocyanate molecules with fiber matrix through the chain of covalent bonds and the interaction of π-electrons of benzene rings of polystyrene as well as isocyanate. As a result, poly[methylene(polyphenyl isocyanate)] forms a bridge between fiber and polymer on the interfaces. This result is instrumental for efficient stress transfer between cellulose fibers and thermoplastics. The performance of different pulps of various wood species as reinforcing fillers for thermoplastic composites is also examined.     

Composites of Polyvinyl Chloride-Wood Fibers. I. Effect of Isocyanate as a Bonding Agent

Various parameters concerning the performance of isocyanate as a coupling agent have been discovered. Greater premixing time (e.g., 20 min) leads to an improvement in the mechanical properties of the composites. the isocyanate solution is more efficient in comparison with undiluted isocyanate. Moreover, the chemical structure of isocyanate, which provides a better interaction with thermoplastics, results in superior properties. the reactivity of different isocyanates decreases in the following order: PMPPIC, TDIC, HMDIC, EIC. Again, isocyanate can act as a promoter or as an inhibitor, depending on the concentration of isocyanate used. For example, with a moderate concentration, it promotes maximum mechanical properties, while with a higher concentration, mechanical properties deteriorate. In addition, the nature of the pulp (e.g., CTMP, cotton, or sawdust) and fiber loading percentage as well as different grades of polymer supplied by different companies also play an important role in the mechanical properties of thermoplastic composities.     

Wood fibers as reinforcing fillers for polyolefins

Wood pulp fibers possess strength and modulus properties which compare favorably with glass fibers when the differences in fiber densities are considered. Softwood pulp fibers with fiber aspect ratios near 100 are readily dispersed into high-density polyethylene or isotactic polypropylene with the aid of carboxyic dispersing agents to form mixtures containing 50 weight-percent wood pulp which can be readily injection molded. The mechanical properties of the molded specimens were similar for all types of pulp including Kraft (bleached and unbleached), mechanical and chemical-mechanical pulps, waste pulps, and reclaim newspapers. Comparisons of the stiffness/weight efficiencies revealed that pulp composites equal or exceed the stiffness of most traditional materials of construction including steel, aluminum, glass-fiber composites, and talefilled polyolefins, while retaining a major material cost advantage. The measured strength values of the pulp composites were less than the theoretically predicted values due to the presence of voids created by the formation of volatiles during processing. Mechanical pulps which were available in dry form were preferred because of lower cost and ease of handling. Wood fibers are non-abrasive so that relatively large concentrations may be incorporated into polyolefins without causing serious machine wear during mixing and fabrication.     

The Mechanical Properties of Wood Fiber-reinforced Polymethylmethacrylate

Abstract

The mechanical properties, e.g. tensile modulus (at 0.1% strain), tensile strength at maximum point and corresponding elongation and breaking energy, as well as impact strength, of compression molded PMMA and PMMA filled with wood fibers (10%-40% by weight of composite) have been investigated. Optimization of molding conditions, (e.g. temperature, time, pressure and mixing aids) was carried out. In optimum conditions of mixing and molding, the effect of different parameters, (e.g. nature and concentration of coupling agents (isocyanates), coating treatment, nature of wood species in the form of various pulps) on the mechanical properties of the resulting composites were evaluated. PMPPIC having 2%-4% (by weight of polymer) was found to behave as a true coupling agent because modulus as well as the tensile and impact strengths were improved. Moreover, PMPPIC acted as a coupling agent even when it was used for treatment of PMMA and fiber or to precoat the fiber. A distinct effect of the morphology of wood species and fiber-making techniques on the mechanical properties of wood fiber-filled composites was also observed.     

Use of wood fibers in thermoplastics. VII. The effect of coupling agents in polyethylene–wood fiber composites

Linear low density polyethylene (LLDPE) was reinforced with different wood fibers, aspen chemithermomechanical pulp (bleached and unbleached), and other commerical wood pulps. Silane coupling agents A-172, A-174, A-1100, and polymethylene polyphenyl isocyanate were used to improve the bonding between the fiber and matrix. LLDPE filled with pretreated wood fiber produced a significant improvement in tensile strength and modulus. Comparison of tensile and impact properties of wood fiber composites with mica and glass fiber composites shows the potential advantage (in terms of material cost and specific properties) of wood fiber as a reinforcement.     

Mechanical properties of natural fibers/polyamides composites

The aim of this investigation has been to use high performance thermoplastic matrices such as polyamides instead of the commonly used polyolefins to develop natural fiber composites for substituting glass fibers without renouncing to their mechanical properties. For this purpose, different natural fibers such as flax, jute, pure cellulose, and wood pulps have been melt compounded with different polyamides to analyze the effect of fiber content on mechanical properties. Fibers have not been treated as polyamides are less hydrophobic than polyolefins. Thermal behavior of the different fibers was determined by thermogravimetry to know the boundary for processing at high temperatures, since the melting points of the polyamides are much higher than those of polyolefins and this could lead to a higher degradation of the natural fibers. Rheological parameters were deduced by measuring torque values during the mixing process. Flexural and tensile modulus and strength of composites were analyzed, finding an increase in the mechanical properties compared with the unreinforced matrix that turns natural fibers into a considerable reinforcement offering a wealth of possibilities for industrial applications. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Lignocellulosic polymer composite IV

Palm leaves as a woody lignocellulose, together with polystyrene, were used to produce composites. Chemithermal mechanical pulps (CTMP) were obtained from palm leaves under alkaline or acidic conditions. Appropriate bending strength was obtained from palm leaves and their CTMP pulps prepared under neutral or acidic conditions. The bulky fibers resulted from the alkaline pulps lead to composites of low bending strength. Thus, the cooking conditions of the palm leaves to obtain CTMP pulp play an important role on the properties of the composites. The nonbulky fibers lead to the formation of trapped pockets air as the number of the hydrogen bond are few. The presence of these air pockets allows the polystyrene solution to enter forming bonding between the interfaces. It is also found that the lower the density of the composites, the lower the internal bond strengths. The chemical constituents of the CTMP pulps, as well as the yields of the pulps, may influence the properties of the composites. Increasing the percentage of polystyrene in the composites, the mechanical properties increased. The water uptake and the swellability decreased until 20% polystyrene concentration and then levelled off. The thickness and density behaved the same. However, the type of substrate of the composite and the weight fraction are the important factors in determining the properties of the composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 845–855, 1998     

Enhancing the strength of polypropylene fibers with carbon nanotubes

Single‐walled carbon nanotubes were added to two different grades of polypropylene to produce composites. The composites were then melt‐spun into fibers, and the fibers were tested with both a conventional tensile pull tester and dynamic mechanical analysis. The changes in tensile properties were related to the grade of polypropylene used. In addition to fibers being made from the mixes, coarse extrudates (i.e., undrawn, gravity‐spun filaments) were also produced. Density measurements on these extrudates showed that the addition of nanotubes increased the composite density in a highly nonlinear manner, which suggested interaction between the polypropylene and the carbon nanotubes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2926–2933, 2004     

Composites of poly(vinyl chloride) and wood fibers. Part II: Effect of chemical treatment

This study examines the influence of different cellulose treatments, including coating by latex or by grafting with polymer/vinyl monomers, as well as with various additive dispersants (e.g., stearic acid or anhydrides) and coupling agents (e.g., maleic anhydride, abietic acid, and linoleic acid). The mechanical properties are examined for poly(vinyl chloride) treated hardwood (chemithermomechanical pulp and sawdust). In most cases, properties are improved compared with untreated composites. Among all methods, grafting was found to be the most effective. Coupling agents show better performance compared with dispersants. Linoleic acid is believed to be the best coupling agent.     

Composites of polyvinyl chloride–wood fibers. III: Effect of silane as coupling agent

The performance of silanes as coupling agents in hardwood aspen fibers (chemithermomechanical pulp and sawdust)—polyvinyl chloride composites, have been investigated. Aside from the chemical structure of silanes, the dispersion aids, e.g. solvent, initiator (different organic peroxides) and maleic anhydride (which provides various chemical reactions as well as physical/chemical inter-actions at the interface), play important roles on the mechanical properties of the composites. In general, the coupling action of silanes is accelerated by the presence of solvents and initiators. But the coupling activity is decelerated when the fibers are coated with polymer latex.     

Effects of short fibers and processing additives on HDPE composites properties reinforced with Pinus and Eucalyptus fibers

This work aimed to investigate the effect of adding short fibers of Pinus and Eucalyptus, in different granulometry (24 and 200 mesh) and concentration (0–20 m/m), combined with processing aid Struktol TPW104 (S) in obtaining of high-density polyethylene (HDPE) composites. Overall, obtaining composites from short fibers caused relevant changes in the HDPE matrix, such as thermal stability, moisture barrier. In comparison to pure HDPE, the composites incorporated with 20% m/m of fibers, regardless of the type, decreased the melting temperature to 128°C and a wider crystallization temperature range. Another significant observation was the improvement of composites mechanical profile after adding the additive, the highest values were obtained for composites HDPEL20PS (35%—TS e 651%—EM) and HDPEL20ES (42%—TS e 681%—EM), showing good interaction and compatibility, according to scanning electron microscopy (SEM) images. The same was verified with the mechanical results of flexion and impact. Therefore, the use of short fibers and processing aid was successful providing augmented mechanical properties and thermal stability, without negatively affecting their essential properties for industrial applications.     

Moisture absorption and wet-adhesion properties of resin transfer molded (RTM) composites containing elastomer-coated glass fibers

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and revealed the importance of changing the surface energy characteristics of glass fibers by using distinctively hydrophobic pure polymers. Admicellar polystyrene and styrene-isoprene coatings formed over the inorganic reinforcement appear to create an interface with much higher resistance to moisture attack than the organosilane/matrix interface in composites with commercial sizing. This fact was corroborated by comparing their effectiveness in property retention, which showed the mechanical property (e.g. ultimate tensile strength, stiffness and interlaminar shear strength) increased with respect to the uncoated composites in the dry state as well as after water saturation. Poor wet-adhesion properties of commercial sizings in humid conditions could perhaps be attributed to higher contents of inert material present in these coatings. Fractography analysis was consistent with the previous observations regarding catastrophic failure in composites without coating, and suggested that interfacial debonding, extensive fiber pullout and matrix crazing were the major contributors to the overall failure mechanism. Failed surfaces of both commercial and elastomer-coated composites also showed areas with fiber pullout, but in this case, matrix residues remained on the fiber surfaces, yielding a much rougher appearance. Good fiber-matrix adhesion, particularly in admicellar-coated composites, was also revealed by the presence of hackles and more tortuous failure paths.     

Surface modification of wood fibers using maleic anhydride and isocyanate as coating components and their performance in polystyrene composites

The effect of surface modification of various wood fibers [e.g. woodflour and chemithermomechanical pulp (CTMP) of hardwood aspen, and woodflour of softwood spruce] by precoating with only maleic anhydride (MA) and/or poly[methylene (polyphenyl isocyanate)] (PMPPIC) in the presence of benzoyl peroxide (BPO) on the mechanical performance of modified fiber-filled polystyrene (PS 201 and PS 525) composites has been studied. The effects of the concentration of fiber, MA, PMPPIC, and BPO on the mechanical properties of the composites have also been evaluated. As opposed to unmodified fiber-filled composites, most of the mechanical properties of the modified fiber-filled composites increased with an increase in the concentration of BPO, MA, and/or PMPPIC up to a certain limit, and then either decreased or levelled off. The properties improved even more when both MA and PMPPIC were used as compared with the use of only one of them. The optimum concentrations of BPO, MA, PMPPIC, and fiber vary according to the wood species, the nature of the fiber, and the type of polystyrene. Compared with woodflour, CTMP is believed to be by far the best as far as the mechanical properties of the modified fiber-filled composites are concerned.     

Corn oil‐based composites reinforced with continuous glass fibers: Fabrication and properties

Novel thermosetting composites have been successfully developed using glass fibers to reinforce regular corn oil (COR) and conjugated corn oil (CCOR) resins prepared by cationic copolymerization with styrene (ST) and divinylbenzene (DVB). The dependence of morphology and physical properties of the composites on the contents of glass fibers and DVB was determined by scanning electron microscopy, dynamic mechanical analysis, thermogravimetric analysis and tensile testing. The glass fiber loading and polymer matrix composition play an important role in improving the mechanical properties and thermal stability of the resulting composites. As the glass fiber content increases from 0 to 45 wt %, the COR‐based composites show an increase in Young's modulus from 4.1 to 874 MPa and tensile strength from 1.7 to 8.4 MPa. Furthermore, the composites exhibit good damping properties and are suitable for applications where reduction of both unwanted noise and vibration is important. Compared with the composites from COR, the CCOR‐based composites exhibit slightly higher thermal stabilities and mechanical properties, due to higher reactivity of CCOR with comonomers. Increasing the DVB content improves the crosslink density of the polymer matrix, leading to a significant improvement in the thermal stabilities and mechanical properties of the resulting composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3345–3353, 2006     

Effect of fiber length on processing and properties of extruded wood‐fiber/HDPE composites

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     

Synergistic effect of graphite nanoplatelets and glass fibers in polypropylene composites

In this study, polypropylene (PP) composites reinforced with short glass fibers (GF) and exfoliated graphite nanoplatelets were obtained by melt compounding followed by injection molding. Morphological observations and quasi‐static tensile tests were carried out in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e., micro‐ and nanoscale). The results indicate that the dispersion of the nanofiller in the PP matrix promoted the formation of a stronger interface between the matrix and GF, as indicated by the increase of the interfacial shear strength determined by the single‐fiber microdebonding test. Concurrently, a significant improvement of the tensile modulus and impact strength of the composites was observed, with small changes in the processability of hybrid composites compared to that of GF composites, as confirmed by rheological measurements. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41682.     

Influence of wood pulp quality on the structure of carboxymethyl cellulose

The quality of carboxymethyl cellulose (CMC) prepared from different wood-derived market pulps is examined. The pulps represent kraft and sulfite qualities with different levels of hemicellulose (1.5–22.8 wt %), intrinsic viscosity (391–780 mL g⁻¹), and content of extractives (0.04–0.13 wt %). The pulps are carboxymethylated in aqueous medium at three different levels of sodium hydroxide concentration, resulting in three levels of degree of substitution (DS), 0.3, 0.7–0.8, and 1.3–1.4 (according to nuclear magnetic resonance spectroscopy and high-performance liquid chromatography). CMC with DS 0.7–0.8 is found to be near the limit for water solubility and the resulting ranking for that solubility is shown to be correlated to DS. The DS is found to be impaired by a high content of impurities and high degree of Cellulose II in the pulp. The sulfite pulps yield CMC with the best solubility in water. A high level of extractives does not interfere with reactivity. Moreover, it is found that impurities, such as lignin and xylan, inhibit thickening behavior even at high DS, and that the ratio of substitution on Position 3 is a measure of the xylan content, which suggests that this position in xylan has extremely high reactivity. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47862.     

Graftability of beaten pulps and acetylated pulps

Ce(IV)-induced polymerization of acrylonitrile with acetylated bagasse and wood pulps, having different acetyl contents, has been investigated. The graft yield is dependent on the acetyl content as well as the origin of the pulp. Increasing the acetyl content of pulps caused a significant decrease in the polymer loading. However, the rate of polymerization of acetylated wood pulp is much higher than that of acetylated bagasse pulp. The ceric consumption during grafting decreases as the acetyl content of the pulp increases. The effect of beating of the pulps, to various degrees of freeness, on their reactivity toward grafting process has also been studied. Generally, the state of cellulose, as defined by its degree of beating, and the origin of the pulp strongly influenced the graft yield. In creasing the beating degree of bagasse pulp resulted in a decrease in graft yield, while beating of wood pulp, to a definite degree, inhibits the polymerization reaction. The consumption of Ce(IV) by the beaten pulps during oxidation is somewhat greater than that consumed by the unbeaten pulps, whereas the consumption during grafting of acrylonitrile onto beaten pulps depends on the initial concentration of ceric solution. Also, the effect of grafting of acrylonitrile onto acetylated wood and bagasse pulps on their strength properties as well as the effect of grafting onto beaten pulps on their properties has been investigated. Grafting of acrylonitrile onto acetylated bagasse pulp decreased its strength properties, but improved its beatability comparatively to those of original pulp (0 acetyl content). On the other hand, grafting of acrylonitrile onto acetylated wood pulp resulted in a great improvement in its strength properties compared to those of grafted unacetylated pulp. Grafted unbeaten pulps gave thinner and weaker paper than the original pulp (without grafting). Beating of bagasse pulp before grafting gave pulp which possessed a higher strength properties, at low °SR, than those of pulp beaten after grafting. Raising the °SR by rebeating the pulp after reaction up to the original value had an adverse effect on the strength. Beating of bagasse pulp before grafting did not accelerate the reaction rate, but it saved some power consumption, since the time required for beating of grafted pulp to a given °SR was lower than that of ungrafted pulp.     

Properties and modification methods for vegetable fibers for natural fiber composites

Studies on structure and properties of natural vegetable fibers (NVF) show that composites made of NVF combine good mechanical properties with a low specific mass. The high level of moisture absorption by the fiber, its poor wettability, as well as the insufficient adhesion between untreated fibers and the polymer matrix lead to debonding with age. To build composites with high mechanical properties, therefore, a surface modification of the fibers is necessary. The existing physical and chemical NVF modification methods—e.g., plasma treatment or graft copolymerization—which are used for the development of NVF–polymer composite properties is discussed. It is shown that modified cellulose fiber–polymer interaction mechanisms are complex and specific to every definite system. By using an coupling agent, like silanes or stearin acid, the Young's modulus and the tensile strength increases, dependent on the resin, until 50%. Simultaneously, the moisture absorption of the composites decreases for about 60%. With other surface modifications, similar results are obtained. © 1996 John Wiley & Sons, Inc.     

Activating pulp toward acetylation by chemical or mechanical means

Activation of pulps during acetylation, by prior mechanical or chemical treatment, has been investigated. The effect of degree of beating on the acetylation rate of wood and bagasse pulps has been studied. It is found that the acetylation rate of pulps increases when the degree of beating of pulps is increased to a definite degree, after which it slows down. The maximum reactivity of bagasse pulp is obtained at 50°SR, while that of wood pulp is observed at 30°SR. The effect of grafting of acrylonitrile onto bagasse and wood pulps on their reactivity during acetylation has been also studied. The results indicate that grafting of acrylonitrile onto pulps has a favorable effect on their acetylation rate. This is dependent on the degree of grafting as well as the origin of pulp fibers. The most suitable method of activation during acetylation reaction is dependent on the origin of the pulp. The reactivity of bagasse pulp during acetylation is influenced more by beating of pulp, prior to the reaction, than by the grafting of acrylonitrile onto pulp. On the other hand, the acetylation reaction of wood pulp is activated by grafting rather than by beating. Also the effect of the activation process, mechanical or chemical, on the strength properties of the paper sheets produced from acetylated pulps has been investigated. Chemical activation of wood pulp prior to acetylation resulted in pulp with slightly higher strength properties than that activated by mechanical means. But, in the case of bagasse pulp, mechanical activation resulted in a pulp with strength superior to that produced by chemical activation.