Dynamic mechanical properties and correlation with dynamic fragility of sisal reinforced composites

In this study, the reinforcement effect in sisal/polyester composites containing distinct reinforcement content was studied ranging from fragile to strong classification. The results indicate that the reduced storage modulus changes steadily, and the loss modulus and the tan δ peak are broader for composites containing more fiber (dynamically strong composites). As more fiber was incorporated in the resin, lower peak height for the tan delta curve was obtained, which may be indicative of lower energy dissipation due to a greater relative amount of interface. Also, the use of reduced dynamic mechanical curves (similar to dynamic fragility) is an alternative to facilitate the study of the material behavior. POLYM. COMPOS., 36:161–166, 2015. © 2014 Society of Plastics Engineers     

The photodegradation and biodegradation of rEPS/curaua fiber composites

The development of composite materials comprised of postconsumer polymers and natural fibers is important for the possibility to obtain materials that are more compatible with the environment. Depending on the application of these materials and their final disposal, the relevant degradation processes must be considered in the studies of these materials. The aim of this work is to evaluate the effect of the degradation process in simulated soil and in the aging accelerated UV chamber on the properties (tensile strength, chemical, morphology) of the composites developed with recycled expanded polystyrene matrix reinforced by curaua fiber. In the tensile strength tests, it was found that the presence of the curaua fiber and the coupling agent did not have significant effect in the degradation processes of the polymer matrix. However, the use of the coupling agent without the addition of fiber curaua promoted the accelerated degradation of the matrix. The carbonyl index was used as the main assessment parameter of the degradation of the composites, since an increasing in the carbonyl index was observed in the initial periods of degradation decreasing for longer time periods. The presence of cracks in the samples following exposure to UV was observed, but no biofilm formation was identified in the samples exposed to the simulated soil. POLYM. COMPOS., 34:967–977, 2013. © 2013 Society of Plastics Engineers     

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

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

Interfacial,dynamic mechanical,and thermal fiber reinforced behavior of MAPE treated sisal fiber reinforced HDPE composites

The present article summarizes an experimental study on the mechanical and dynamic mechanical behavior of sisal fiber reinforced HDPE composites. Variations in mechanical strength, storage modulus (E′), loss modulus (E″), and damping parameter (tan δ) with the addition of fibers and coupling agents were investigated. It was observed that the tensile, flexural, and impact strengths increased with the increase in fiber loading up to 30%, above which there was a significant deterioration in the mechanical strength. Further, the composites treated with MAPE showed improved properties in comparison with the untreated composites. Dynamic mechanical analysis data also showed an increase in the storage modulus of the treated composites The tan δ spectra presented a strong influence of fiber content and coupling agent on the α and γ relaxation process of HDPE. The thermal behavior of the composites was evaluated from TGA/DTG thermograms. The fiber–matrix morphology in the treated composites was confirmed by SEM analysis of the tensile fractured specimens. FTIR spectra of the treated and untreated composites were also studied, to ascertain the existence of type of interfacial bonds. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3306–3315, 2006     

Mechanical properties and dynamic mechanical analysis of thermoplastic‐natural‐rubber‐reinforced short carbon fiber and kenaf fiber hybrid composites

The hybridization of thermoplastic natural rubber based on carbon fiber (CF) and kenaf fiber (KF) was investigated for its mechanical and thermal properties. Hybrid composites were fabricated with a melt‐blending method in an internal mixer. Samples with overall fiber contents of 5, 10, 15, and 20 vol % were subjected to flexural testing, and samples with up to 30% fiber content were subjected to impact testing. For flexural testing, generally, the strength and modulus increased up to 15 vol % and then declined. However, for impact testing, higher fiber contents resulted in an increment in strength in both treated and untreated composites. Thermal analysis was carried out by means of dynamic mechanical analysis on composites with 15 vol % fiber content with fractions of CF to KF of 100/0, 70/30, 50/50, 30/70, and 0/100. Generally, the storage modulus, loss modulus, and tan δ for the untreated hybrid composite were more consistent and better than those of the treated hybrid composites. The glass‐transition temperature of the treated hybrid composite was slightly lower than that of the untreated composite, which indicated poor damping properties. A scanning electron micrograph of the fracture surface of the treated hybrid composite gave insight into the damping characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and dynamic mechanical properties of epoxy syntactic foams reinforced by short carbon fiber

Epoxy syntactic foams were prepared with diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin, 2.4.6‐tri(dimethylaminomethyl)phenol (DMP‐30), coupling treated microsphere and short carbon fiber. The density of the foam was maintained between 0.56 and 0.91 g/cm³ for all compositions. Compressive, flexural, tensile and dynamic mechanical properties of the foams were investigated with respect to hollow glass microsphere (HGM) and carbon fiber (CF) content. A considerable improvement in the mechanical properties viz. compressive, flexural and tensile strengths was observed for the foams on incorporation of a small quantity of CF. The storage modulus were higher for the foam composites containing CF. The presence of HGM has significant influence on T_g of the syntactic foams, spherical filler diminished the T_g of the syntactic foams due to the plasticizing effect of the coupling treatment of HGM, that is helpful for enhancing damping properties of syntactic foams. POLYM. COMPOS., 37:1960–1970, 2016. © 2015 Society of Plastics Engineers     

Mechanical properties of biorenewable fiber/plastic composites

Plastic fiber composites, consisting of polypropylene (PP) or polyethylene (PE), and pinewood, big blue stem (BBS), soybean hulls, or distillers dried grain and solubles (DDGS), were prepared by extrusion. Young's modulus, tensile and flexural strengths, melt flow, shrinkage, and impact energy, with respect to the type, amount, and size of fiber on composites, were evaluated. Young's moduli under tensile load of wood, BBS, and soybean‐hull fiber composites, compared with those of pure plastic controls, were either comparable or higher. Tensile strength significantly decreased for all the PP/fiber composites when compared with that of the control. Strength of BBS fiber composites was higher than or comparable to that of wood. When natural fibers were added there was a significant decrease in the melt flow index for both plastic/fiber composites. There was no significant difference in the shrinkage of all fiber/plastic composites compared to that of controls. BBS/PE plastic composites resulted in higher notched impact strength than that of wood or soybean‐hull fiber composites. There was significant reduction in the unnotched impact strength compared to that of controls. BBS has the potential to be used as reinforcing materials for low‐cost composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2484–2493, 2004     

Mechanical properties and foaming behavior of cellulose fiber reinforced high‐density polyethylene composites

This article investigates the effects of fiber length and maleated polymers on the mechanical properties and foaming behavior of cellulose fiber reinforced high‐density polyethylene composites. The results from the mechanical tests suggested that long fibers provided higher flexural and impact properties than short fibers. In addition, the maleated high‐density polyethylene increased flexural strength significantly, while the maleated thermoplastic elastormers increased notched Izod impact strength dramatically. On the other hand, the results from the extrusion foaming indicated that the composites with long and short fibers demonstrated similar cell morphology, i.e., a similar average cell size and cell size distribution. However, the addition of maleated high‐density polyethylene caused an increase of the average cell size and cell size distribution in the composites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effect of degree of cure and fiber content on the mechanical and dynamic mechanical properties of carbon fiber reinforced PMR-15 polyimide composites

A unidirectional continuous carbon fiber reinforced polyimide composite is fabricated using the PMR-15 polyimide as a matrix. Mechanical and dynamic mechanical properties of the composite are studied. The effect of variation of the fiber content ranging from 55% to 70% by volume on the properties of the composite is determined. The effects of the laminate thickness and degree of curing of the matrix on the Izod impact strength are examined. The effect of the degree of curing of the matrix on the dynamic mechanical spectrum is studied. Finally, variables such as humidity, environment temperature, vacuum, and pressure during laminate processing, and variation of monomer composition are discussed in terms of change in matrix structure, which is reflected in a variation of Tg between batches.     

Effect of natural fibers on thermal and mechanical properties of natural fiber polypropylene composites studied by dynamic mechanical analysis

The present study deals with the effects of natural fibers on thermal and mechanical properties of natural fiber polypropylene composites using dynamic mechanical analysis. Composites of polypropylene and various natural fibers including kenaf fibers, wood flour, rice hulls, and newsprint fibers were prepared at 25 and 50% (by weight) fiber content levels. One and two percent maleic anhydride grafted polypropylene was also used as the compatibilizer for composites containing 25 and 50% fibers, respectively. Specimens for dynamic mechanical analysis tests were cut out of injection‐molded samples and were tested over a temperature range of ?60 to +120°C. Frequency of the oscillations was fixed at 1 Hz and the strain amplitude was 0.1%, which was well within the linear viscoelastic region. The heating rate was 2°C/min for all temperature scan tests. Storage modulus (E′), loss modulus (E″), and mechanical loss factor (tan δ) were collected during the test and were plotted versus temperature. An increase in storage and loss moduli and a decrease in the mechanical loss factor were observed for all composites indicating more elastic behavior of the composites as compared with the pure PP. Changes in phase transition temperatures were monitored and possible causes were discussed. Results indicated that glass transition was slightly shifted to lower temperatures in composites. α transition temperature was higher in the case of composites and its intensity was higher as well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4341–4349, 2006     

Dynamic mechanical properties of pineapple leaf fiber polyester composites

In the recent years, lignocellulosic fibers that originate from a renewable source have been found to provide good reinforcement in polymer matrices. Among the natural fibers, pineapple leaf fiber (PALF) exhibits excellent mechanical properties, besides possessing low density, high stiffness, and low cost. The dynamic mechanical properties, storage modulus (E′), and loss tangent of PALF‐reinforced polyester (PER) composites were evaluated at three frequencies 0.1, 1, and 10 Hz and temperatures ranging from 30 to 200°C. Addition of PALF of 30 mm length (aspect ratio 600) was found to increase the storage modulus leading to a maximum value at 40 wt%. The glass transition temperature (T_g) of the composite of 40 wt% showed a positive shift indicating high polymer/fiber interaction. A new relaxation is observed at 40 wt% showing the presence of a strong interphase at all aspect ratios. SEM photographs of fracture surfaces of composites confirm the results obtained from static and dynamic mechanical analysis. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Investigation of the dynamic mechanical behavior of polypropylene/(wood flour)/(kenaf fiber) hybrid composites

Polypropylene/(wood flour)/(kenaf fiber) hybrid composites were prepared in an internal mixer. Kenaf was considered as a fibrous filler and wood flour as a particulate filler. The lignocellulosic loading used was 50%. Dynamic mechanical thermal analysis properties such as storage modulus (E′), loss modulus (E″), damping factor (tan δ), and adhesion factor were evaluated. It was found that the adhesion factor could interpret the interfacial adhesion between lignocellulosic fillers and the plastic matrix macroscopically. This factor was affected by the type of filler used and the coupling agent concentration. The variation of storage modulus was affected more by the shape of the filler and the coupling agent concentration at higher temperatures than at temperatures below the glass transition. Owing to a higher probability of agglomeration in a sample containing 50 wt% of wood flour, the storage modulus and complex viscosity of this sample were higher than those of other samples. Cole‐Cole diagrams showed that the homogeneity of samples containing a higher amount of coupling agent was higher than that of samples with a lower concentration. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Study of jute fiber reinforced polyester composites by dynamic mechanical analysis

Cyanoethylation of jute fibers in the form of nonwoven fabric was studied, and these chemically modified fibers were used to make jute–polyester composites. The dynamic mechanical thermal properties of unsaturated polyester resin (cured) and composites of unmodified and chemically modified jute–polyester were studied by using a dynamic mechanical analyzer over a wide temperature range. The data suggest that the storage modulus and thermal transition temperature of the composites increased enormously due to cyanoethylation of fiber. An increase of the storage modulus of composites, prepared from chemically modified fiber, indicates its higher stiffness as compared to a composite prepared from unmodified fiber. It is also observed that incorporation of jute fiber (both unmodified and modified) with the unsaturated resin reduced the tan δ peak height remarkably. Composites prepared from cyanoethylated jute show better creep resistance at comparatively lower temperatures. On the contrary, a reversed phenomenon is observed at higher temperatures (120°C and above). Scanning electron micrographs of tensile fracture surfaces of unmodified and modified jute–polyester composites clearly demonstrate better fiber–matrix bonding in the case of the latter. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1505–1513, 1999     

Rheological behavior and mechanical properties of sawdust/polyethylene composites

We have characterized the melt rheological behavior and the solid tensile properties of sawdust/polyethylene composites prepared in an internal mixer. Various concentrations (from 0 to 60 wt %) and three particle sizes have been tested, in presence of a coupling agent (maleic anhydride grafted polyethylene). In the molten state, for each particle size, a mastercurve of the complex viscosity as function of frequency can be plotted, using a shift factor depending on weight fraction. We show that the shift factors can be described by a Krieger‐Dougherty law, leading to a “universal” viscosity law of the Carreau‐Yasuda type. In the solid state, the presence of sawdust increases Young modulus in uniaxial elongation, mainly for small size particles, but reduces dramatically deformation at break and tensile strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

纤维表面处理对复合材料力学性能的影响

本文研究了碳纤维表面处理方法对纤维-基体界面剪切强度的影响．研究结果表明，相对于未进行表面处詈的碳纤维-所采用的胺基化处理和偶联剂处理两种表面处理方法都能够提高碳纤维界面的剪切强度，从而提高复合材料整体的抗拉强度和弹性模量。并且偶联剂处理方法具有更好的工艺性．     

Crystallization behavior and mechanical properties of polypropylene/halloysite composites

In this work, halloysite nanotubes (HNTs), a new type of inexpensive filler, were used for the modification of polypropylene (PP). HNTs were first surface treated by methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium, then melt mixed with PP. Scanning electron microscope (SEM) was used to examine the dispersion of HNTs in PP matrix. Differential scanning calorimetry (DSC), polarized light microscope (PLM), dynamic melt rheometry and wide angle X-ray diffraction (WAXD) were employed to investigate the crystallization behavior of the prepared PP/HNT composites. The mechanical properties were evaluated by Instron and impact tests. SEM results revealed that HNTs could be well-dispersed in PP matrix and had a good interfacial interaction with PP, even up to a high content of 10 wt%. DSC data indicated that HNTs could serve as a nucleation agent, resulting in an enhancement of the overall crystallization rate and the non-isothermal crystallization temperature of PP. PLM showed a constant spherulite growth rate and a decreased spherulite size at given isothermal crystallization temperature, suggesting that nucleation and growth of a spherulite are two independent processes. The result obtained by dynamic melt rheometry indicated that HNTs mainly promoted nucleation and had not much influence on the growth of PP crystallization. Nevertheless, by fast cooling the samples, almost constant spherulite size can be obtained for both pure PP and PP/HNT composites due to the limited nucleation effect of HNTs on PP crystallization. WAXD showed that HNTs mainly facilitated α-crystal form of PP. Though a good dispersion of HNTs in PP matrix was observed, out of our expectation, not much enhancement on mechanical properties of PP/HNT composites had been achieved, and this could be mainly ascribed to the constant crystallinity and spherulite size of PP as well as the small length/diameter ratio of HNTs.     

The role of additives in the manufacture of sheets of unsaturated polyester and postconsumer unsaturated polyester/glass fiber composites: Mechanical and dynamic mechanical properties

The storage of postconsumer glass fiber reinforced unsaturated polyester composite impacts negatively on the environment because of the long lifetime and the volume/amount ratio of residuals, which are important aspects to be considered. Two types of additives were employed as an attempt to improve the mechanical properties of sheets manufactured with ground postconsumer glass fiber reinforced orthophthalic unsaturated polyester resin composite and virgin orthophthalic unsaturated polyester resin, a silane‐coupling agent and an organic dispersant. Flexural and impact tests, and dynamic mechanical analyses, demonstrated that the coupling agent increased the mechanical properties, while the dispersant decreased these properties, compared to material without either additive. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1834–1839, 2004     

Effect of fiber treatment on the mechanical properties of LDPE-henequen cellulosic fiber composites

The degree of mechanical reinforcement that could be obtained by the introduction of henequen cellulosic fibers in a low-density polyethylene, LDPE, matrix was assessed experimentally. Composite materials of LDPE-henequen cellulosic fibers were prepared by mechanical mixing. The concentration of randomly oriented fibers in the composite ranged between 0 and 30% by volume. The tensile strength of these composite materials increased up to 50% compared to that of LDPE. There is also a noticeable increase in Young's modulus for the composite materials that compares favorably with that of LDPE. As expected, the addition of the fibers decreases the ultimate strain values for the composite materials. The thermal behavior of the LDPE-henequen cellulosic fibers materials, studied by differential scanning calorimetry, DSC, showed that the presence of the fibers does not affect the thermal behavior of the LDPE matrix; thus, the interaction between fiber and matrix is probably not very intimate. Preimpregnation of the cellulosic fibers in a LDPE-xylene solution and the use of a silane coupling agent results in a small increment in the mechanical properties of the composites, which is attributed to an improvement in the interface between the fibers and the matrix. The shear properties of the composites also increased with increasing fiber content and fiber surface treatment. It was also noted that the fiber surface treatment improves fiber dispersion in the matrix. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 197–207, 1997