Effects of alkaline and silane treatments on the water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites

The water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites (WRPCs) prepared from postconsumer high‐density polyethylene (HDPE) and wood fibers from saw mills were studied. Three methods consisting of an alkaline method (AM), a silane method (SM), and a combination of the alkaline and silane methods (ASM) were used to modify the wood fibers. The effects of fiber/matrix mix ratio and surface treatment on the moisture content, thickness swelling, and flexural strength change of the WRPCs, before and after immersion in 60°C water for 8 weeks, were studied and analyzed. The flexural fractured surfaces of the WRPCs before and after immersion in hot water were examined, and the fracture mechanism of the WRPCs was discussed. The results showed that the different surface treatments of the wood fibers had significant effects on the moisture content, thickness swelling, and flexural strength of the WRPCs after a long immersion time in hot water. For WRPCs treated by ASM, the moisture content was the lowest, the thickness swelling was at a minimum, and the flexural strength was the highest. Higher water absorption of composites with fiber treated by the AM or SM methods, as compared to those treated by ASM, could be attributed to the incomplete adhesion and wettability between the wood fibers and the polymer matrix, which may have caused more gaps and flaws at the interface. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Effects of alkali and silane treatment on the mechanical properties of jute‐fiber‐reinforced recycled polypropylene composites

Jute‐fibers‐reinforced thermoplastic composites are widely used in the automobile, packaging, and electronic industries because of their various advantages such as low cost, ease of recycling, and biodegradability. However, the applications of these kinds of composites are limited because of their unsatisfactory mechanical properties, which are caused by the poor interfacial compatibility between jute fibers and the thermoplastic matrix. In this work, four methods, including (i) alkali treatment, (ii) alkali and silane treatment, (iii) alkali and (maleic anhydride)‐polypropylene (MAPP) treatment, and (iv) alkali, silane, and MAPP treatment (ASMT) were used to treat jute fibers and improve the interfacial adhesion of jute‐fiber‐reinforced recycled polypropylene composites (JRPCS). The mechanical properties and impact fracture surfaces of the composites were observed, and their fracture mechanism was analyzed. The results showed that ASMT composites possessed the optimum comprehensive mechanical properties. When the weight fraction of jute fibers was 15%, the tensile strength and impact toughness were increased by 46 and 36%, respectively, compared to those of untreated composites. The strongest interfacial adhesion between jute fibers and recycled polypropylene was obtained for ASMT composites. The fracture styles of this kind of composite included fiber breakage, fiber pull‐out, and interfacial debonding. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers.     

Mechanical properties and water absorption of fiber‐reinforced polypropylene composites prepared by bagasse and beech fiber

The present study investigates the tensile, flexural, notched Izod impact, and water absorption properties of bagasse and beech reinforced polypropylene (PP) composites as a function of fiber content. The surface of fibers was modified through the use of maleated polypropylene (MAPP) coupling agent. From this study, it was found that mechanical properties increase with an increase in fiber loading in both cases. However, the addition of wood fibers resulted in a decrease in impact strength of the composites. The water absorption property at varying fiber loading was evaluated and found maximum for the BA/PP composites. The weight gains for all specimens were less than 7%. In general, the results showed the usefulness of bagasse fiber as a good alternative and reinforcing agent for composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Localized thermal analysis of carbon fiber‐reinforced polypropylene composites

The effect of carbon fiber (CF) and annealing temperature on polypropylene (PP) microstructure was studied. The crystalline state of polymer matrix was found to be a strong function of thermal history. The effect of annealing temperature on the microstructure evolution of PP in the presence of CFs was characterized by using X‐ray diffraction, DSC and localized thermal analysis. The melting behavior of CF‐reinforced PP composite was strongly dominated by the thermal history and was weakly influenced by the presence of CFs. The interface between a CF and PP matrix was found to be weak. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Fabrication and properties of nano‐ZnO/glass‐fiber‐reinforced polypropylene composites

Polypropylene (PP) is widely used in many fields, such as automobiles, medical devices, office equipment, pipe, and architecture. However, its high brittle transformation temperature, low mechanical strength, dyeing properties, antistatic properties, and poor impact resistance, considerably limit its further applications. Nano‐ZnO treated by KH550 coupling agent and glass fibers (GFs) were introduced in order to improve the mechanical performance and flowability of PP in this research. The crystallization behavior and microstructure of nano‐ZnO/GFs/PP hybrid composites were analyzed by differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy. The effect of crystallization behavior on the mechanical properties of the nanocomposites was investigated and analyzed. The results indicated that nano‐ZnO surface‐coupled by KH550 could be uniformly dispersed in the PP matrix. The incorporation of nano‐ZnO and GFs resulted in increases of the crystallization temperature and crystallization rate of PP and a decrease of the crystallization degree. The introduction of nano‐ZnO and GFs also enhanced the tensile strength and impact toughness of the hybrid composites and improved their fluidity. Composites containing 2% of nano‐ZnO and 40% of GFs possessed the optimum mechanical properties. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Preparation and mechanical properties of high‐performance short ramie fiber‐reinforced polypropylene composites

Short ramie fiber (RF) was used to reinforce the polypropylene (PP). The composites were prepared in a twin‐screw extruder followed by injection molding. The experimental results showed that both the strength and the modulus of the composites increase considerably with increasing RF content. The tensile strength and flexural strength are as high as 67 and 80 MPa by the incorporation of ramie up to 30 wt %. To the best of our knowledge, this is one of the best results for short natural fiber‐reinforced PP composites. However, the preparation method in this study is more simple and economic. This short RF‐reinforced PP composites extend the application field for short‐nature fiber‐reinforced PP composites. Morphological analysis revealed that it is the high aspect ratio of the fiber and good interfacial compatibility that result in the high performance of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Recycled‐disposable‐chopstick‐fiber‐reinforced polypropylene green composites

The utilization of disposable chopsticks is very popular in Taiwan, China, and Japan and is one of the major sources of waste in these countries. In this study, recycled disposable chopstick fiber was chemically modified. Subsequently, this modified fiber and polypropylene‐graft‐maleic anhydride were added to polypropylene (PP) to form novel fiber‐reinforced green composites. A heat‐deflection temperature (HDT) test showed an increase of approximately 81% for PP with the addition of 60‐phr fibers, and the HDT of the composite could reach up to 144.8°C. In addition, the tensile strength, Young's modulus, and impact strength were 66, 160.3, and 97.1%, respectively, when the composite material was 40‐phr fibers. Furthermore, this type of reinforced PP would be more environmentally friendly than an artificial‐additive‐reinforced one. It could also effectively reduce and reuse the waste of disposable chopsticks and lower the costs of the materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Kudzu fiber‐reinforced polypropylene composite

Kudzu fiber‐reinforced polypropylene composites were prepared, and their mechanical and thermal properties were determined. To enhance the adhesion between the kudzu fiber and the polypropylene matrix, maleic anhydride‐grafted polypropylene (MAPP) was used as a compatibilizer. A continuous improvement in both tensile modulus and tensile strength was observed up to a MAPP concentration of 35 wt %. Increases of 24 and 54% were obtained for tensile modulus and tensile strength, respectively. Scanning electron microscopy (SEM) showed improved dispersion and adhesion with MAPP. Fourier transform infrared (FTIR) spectroscopy showed an increase in hydrogen bonding with an increase in MAPP content. Differential scanning calorimetry (DSC) analysis indicated little change in the melting temperature of the composites with changes in MAPP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1961–1969, 2002     

Short jute fiber‐reinforced polypropylene composites: Dynamic mechanical study

Short jute fiber‐reinforced polypropylene (PP) composites were prepared using a high‐speed thermokinetic mixer. A compatibilizer was used to improve the molecular interaction between jute and PP. Both the percent weight fraction of the jute fiber and compatibilizer were varied to study the dynamic mechanical thermal (DMT) properties. Dynamic parameters such as storage flexural modulus (E′), loss flexural modulus (E″), storage shear modulus (G′), loss shear modulus (G″), and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode. The transition peak nature, amplitude, and temperature of E′, E″, G′, G″, and tan δ of different compositions were shown to indicate possible improvements of molecular interaction in the presence of a compatibilizer. The modulus retention term, a plot of the reduced modulus with the weight fraction of the jute fiber, also indicate its improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 531–539, 1999     

Flow‐induced warpage of injection‐molded TLCP fiber‐reinforced polypropylene composites

The most common belief is that warpage in injection‐molded fiber‐reinforced thermoplastics is primarily attributed to residual thermal stresses associated with shrinkage and thermal contraction of the parts. Therefore, it is assumed that flow‐induced stresses generated during mold filling do not play a significant role. Injection‐molded plaques of polypropylene (PP) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) microfibrils were generated in order to investigate the role of residual flow‐induced stresses relative to that of thermal stresses on the warpage. In an effort to relate the material parameters to warpage, the rheological behavior of these fiber‐filled systems was investigated. The shrinkage and the thermal expansion of the TLCP/PP composites, and hence, the thermally induced stresses decreased with an increase in fiber loading while the flow‐induced stresses increased. The increase in the flow‐induced stresses was attributed to increased relaxation times (this is not the only cause, but is a significant factor) with an increase in fiber loading. Therefore, it was found that in order to accurately predict the warpage of fiber‐reinforced thermoplastics, the flow‐induced residual stresses must be accounted for. It is expected that the results reported here can be extended to glass‐reinforced PP composites as well. POLYM. COMPOS., 27:239–248, 2006. © 2006 Society of Plastics Engineers     

Evaluation of dynamic elastic properties of wood‐filled polypropylene composites

Dynamic modulus of elasticity (MoE) and shear modulus of wood‐filled polypropylene composite at various filler contents ranging from 10% to 50% was determined from the vibration frequencies of disc‐shaped specimens. Wood filler was used in both fiber form (pulp) and powder form (wood flour). A novel compatibilizer, m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate(m‐TMI) grafted polypropylene with isocyanate functional group was used to prepare the composites. A linear increase in dynamic MoE, shear modulus, and density of the composite was observed with the increasing filler content. Between the two fillers, wood fiber filled composites exhibited slightly better properties. At 50% filler loading, dynamic MoE of the wood fiber filled composite was 97% higher than that of unfilled polypropylene. Halpin‐Tsai model equation was used to describe the changes in the composite modulus with the increasing filler content. The continuous improvement in elastic properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low‐modulus polypropylene matrix with the high‐modulus wood filler. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1706–1711, 2006     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

In situ fiber‐reinforced composites from blends containing polypropylene and polycaprolactone

Our study was focused on the presupposition that morphology control in immiscible polymer blend could give rise to reinforcement in composites. To investigate the effects of shear and elongational flow in polymer processing, observation of the mechanical properties and the morphology of the polypropylene/polycaprolactone (PP/PCL) blend system was performed. PP/PCL sheets were fabricated by means of a single‐screw extruder equipped with a slit‐type die to which high shear and elongational stresses were applied. For the sake of comparison, a second series of composites of identical composition was compression molded with a hot‐press machine that transmits lower shear and elongational stresses. The results indicate that the extruded sheets have better mechanical properties than those of the compression‐molded sheets, a result attributed to the generation of in situ dispersed long fiber minor phases and cocontinuous phases in the extruded composites. The differences in the crystallization behavior of the fibrous and spherically shaped components were indicated clearly by DSC curves. A PP crystalline peak indicative of in situ PP fiber formation is conspicuous around 980 cm⁻¹ (PP crystalline band) in the FTIR spectrum. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 833–840, 2004     

Mechanical properties and viscoelastic behavior of basalt fiber‐reinforced polypropylene

In the present article, a series of commercial‐grade polypropylenes (PP) filled with different contents of short basalt fibers were studied. This composite material presented deterioration of both mechanical characteristics, for example, stress and strain at yield with increasing of the fiber content. On the other hand, the impact strength was fourfold higher than that of unfilled PP. A poor adhesion between the PP matrix and the basalt fibers was detected. This is why interfacial interactions were promoted by the adding of poly(propylene‐g‐maleic anhydride) (PP‐g‐MA). It was observed that the tensile properties of the obtained materials and their impact strengths increased significantly with increasing of the amount of PP‐g‐MA in the blend. The adhesion improvement was confirmed by scanning electron microscopy as well. Fourier transform infrared spectroscopy was applied to assess if any chemical interactions in the system PP/PP‐g‐MA/basalt fibers exist. Dynamic mechanical thermal analysis data showed an increase of the storage modulus with increasing fiber content. The conclusion was made that the modification of the PP matrix led to a higher stiffness but its value remained constant, irrespective of the PP‐g‐MA content. With increasing fiber content, damping in the β‐region decreased, but increase of the coupling agent content restored its value back to that of PP. The loss modulus spectra presented a strong influence of fiber content on the α‐relaxation process of PP. The position of the peaks of the above‐mentioned relaxation processes are discussed as well. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 523–531, 1999     

The effect of fiber concentration on mechanical and thermal properties of fiber‐reinforced polypropylene composites

A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene‐co‐ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP–PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%, 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber–matrix interaction. A higher concentration of long fibers (>50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox–Krenchel and Haplin–Tsai equations were used to predict tensile modulus of random fiber‐reinforced composites. A Cole–Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time–temperature superposition (TTS) by using data over the temperature range from −50 to 90°C, which allowed for the prediction of very long and short time behavior of the composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2260–2272, 2005     

Acoustic emission characterization of damage in short hemp‐fiber‐reinforced polypropylene composites

This article aims at investigating the effects of hygrothermal aging on the damage mechanisms of short white Hemp Fiber Reinforced Polypropylene (HFRP) composites with various fiber contents (10, 20, 30, and 40 wt%). Injected molded specimens were subjected to hygrothermal aging with a relative humidity of 80% and two temperatures, 25 and 50°C. The water absorption and its effect on tensile properties of HFRP composites were investigated. The Acoustic Emission (AE) technique combined with scanning electron microscopy observations was used to identify microstructural damage events leading to overall failure of the HFRP composites. This identification according to hemp‐fiber content and hygrothermal aging was made with an unsupervised method based on a statistical multi‐variable analysis (k‐means algorithm). The AE results indicate that the quality of fiber‐matrix interface plays a major role in the damage process of HFRP composites, shown by the number of AE signals induced by the interface failure and their amplitude ranges. POLYM. COMPOS. 37:1101–1112, 2016. © 2014 Society of Plastics Engineers     

Performance of long glass fiber‐reinforced polypropylene composites at different injection temperature

Long glass fiber‐reinforced polypropylene composites were prepared using self‐designed impregnation device. Effects of the different injection temperature on mechanical properties, crystallization, thermal, and dynamic mechanical properties of long glass fiber‐reinforced polypropylene composites were discussed. The differential scanning calorimetry (DSC) results indicate that the melting peak temperature of PP/LGF composites gradually reduced, however, the crystallinity of PP/LGF composites gradually increased with increasing injection temperature. Thermo‐gravimetric analyzer (TGA) results demonstrate that with increasing injection temperature, the temperature of the PP/LGF composites melt increased, the viscosity of the PP/LGF composites melt lowered, the mold filling of the PP/LGF composites melt was easy, the shear force of glass fiber was relatively low, which made the residual length of glass fiber in products increase. Dynamic thermal mechanical analyzer (DMA) results show that the storage modulus of PP/LGF composites is the highest while the injection temperature is at 290°C, and the peak value of tan σ of PP /LGF composites at 290°C is minimal, which indicates that the mechanical properties of PP /LGF composites at 290°C is the best. What' more, the injection temperature at 290°C significantly ameliorated “glass fiber rich skin” of products of glass fiber‐reinforced composites. J. VINYL ADDIT. TECHNOL., 24:233–238, 2018. © 2016 Society of Plastics Engineers     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers     

Processing‐interphase‐property relationship in fiber‐reinforced thermosetting‐matrix composites

Fabrication of thermosetting‐matrix composites is based on a critical step of cure, which involves applying a predefined temperature cycle to a fiber‐resin mixture. Several temperature‐dependent mass transport processes occur in the vicinity of the reinforcement fiber, leading to the formation of an interphase region with different chemical and physical properties from the bulk resin. The cure cycles applied on the macroscopic boundaries of the composite govern the microscopic cure kinetics near the fiber surface, which in turn determines the interphase and composite properties. A predictive approach to directly linking the cure cycles and final composite properties is not presently available and is established for the first time in this paper. A multiscale thermochemical model is developed to predict the concentration profile evolution with time near fiber surfaces at various locations across the composite thickness. The concentration profiles at the gelation time are mapped to modulus profiles within the interphase region, and a finite element analysis is used to determine the overall composite modulus in terms of the constituent interphase, fiber, and matrix properties. Relevant numerical results are presented for the first time where the composite modulus is directly linked to the cure cycle and interphase formation parameters without assumed structures or properties of the interphase. The results provide useful information for selecting material components and cure cycles parameters to achieve desired interphase and composite properties. POLYM. COMPOS., 26:193–208, 2005. © 2005 Society of Plastics Engineers     

A comparative study on mechanical properties and water absorption behavior of fiber‐reinforced polypropylene composites prepared by OCC fiber and aspen fiber

Fiber‐reinforced polymers have received considerable attention from industry in recent years. Due to the sharp ecological damage, worldwide shortage of trees in many areas and the global demand for fibrous material, there has been growing interest in the use of recycled wood fiber as an alternative or substitute fiber source. The present study investigates the tensile, flexural, Izod impact, and water absorption behavior of Old Corrugated Container (OCC) and aspen (AS) reinforced polypropylene (PP) composites as a function of fiber content. The surface of AS and OCC fibers was modified through the use of MAPP coupling agent. From the studies it was found that mechanical properties increase with increase in fiber loading in both cases. However the addition of wood fibers resulted in a decrease in impact strength of the composites. The water absorption property at varying fiber loading were evaluated and found maximum for the OCC/PP composites. The weight gains for all specimens were less than 3.5%. Finally, the results showed the usefulness of OCC fiber as a good alternative and reinforcing agent for composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers