Effect of different fiber loadings and sizes on pultruded kenaf fiber reinforced unsaturated polyester composites

Application of the available natural resources became crucial for developing sustainability recently. The use of natural fiber as reinforced materials in polymer composite materials is gaining new interest from within industry. In this research, the effect of different fiber loadings and different types of kenaf yarns, used on the properties of Pultruded Kenaf Fiber Reinforced Composites (PKFRC), was studied. The pultruded composite samples were prepared with different fiber loadings and sizes (tex) of kenaf fiber. Three different fiber loadings, i.e., 60, 65, and 70% were used during the preparation of the PKFRC samples. Flexural and compression testing was performed, to study the effect of different fiber loadings and different kenaf fiber yarns, on the mechanical properties of kenaf fiber pultruded composites. The results show that the highest fiber loading of 70% gave more desirable flexural and compression properties to the PKFRC. The use of twist kenaf yarn fiber showed lower mechanical properties of PKFRC as compared to the single kenaf yarn. Damage configurations and accumulations for each loading case were examined. A morphological study, using optical microscopy (OM) revealed the type of fracture that occurred in the pultruded samples after mechanical testing. POLYM. COMPOS., 36:1224–1229, 2015. © 2014 Society of Plastics Engineers     

不饱和树脂玻璃钢复合材料防老化研究进展

综述了不饱和树脂基玻璃钢复合材料(GFRP)防老化方面的新近研究进展,包括新型GFRP表面涂层及不饱和树脂的防老化添加剂(紫外线吸收剂、受阻胺光稳定剂和抗氧剂等)及树脂的改性。将抗氧剂和其他添加剂(例如某些环氧化合物)并用,可取得较好的效果。     

Physico-mechanical studies of wood fiber reinforced composites

Wood polypropylene composites (WPC) of different compositions (30, 40, and 50%) have been prepared using maleic anhydride–polypropylene copolymer of different percentage (5 and 10% relative to their wood fiber content). Tensile, flexural, fracture toughness, and impact test of the prepared WPC were carried out. From the results, it is observed that the hard wood fiber–polypropylene composites, by using maleated polypropylene (MAH-PP), show comparatively better performance to soft wood fiber–polypropylene composites. Tensile strength and charpy impact strength have been increased to a maximum of 50 and 20%, respectively. The damping index has been decreased by 60% when 10% of MAH-PP has been used. Water absorption and scanning electron microscopy of the composites are also investigated.     

Water absorption of hemp fiber/unsaturated polyester composites

The water absorption of hemp fiber/unsaturated polyester composites was determined by immersing the samples in water or by exposing them to air with a relative humidity of 94%. The water absorption increased with increasing fiber content. By using images obtained with a magnetic resonance imaging (MRI) system, the moisture absorption process was shown to follow a diffusion mechanism and to be more important in the longitudinal than in the transverse direction. The longitudinal diffusion coefficient was computed to be about 3 × 10^–11 m²/s. Composite samples immersed in water reached saturation levels after about eight months and showed no signs of cracking due to swelling. Fibers reached the same saturation limit whether submerged in water or exposed to saturated air when fiber content was less than 21 vol%. Various fiber treatments were tested but none resulted in a substantial increase of the resistance to water absorption. The most effective technique to enhance moisture resistance was to properly seal all the fibers within the matrix. POLYM. COMPOS. 26:509–525, 2005. © 2005 Society of Plastics Engineers     

Impact of delignification on mechanical,morphological, and thermal properties of wood sawdust reinforced unsaturated polyester composites

Mechanical, morphological, and thermal properties of the raw and delignified wood sawdust (DWS) reinforced unsaturated polyester (UP) composites were evaluated. Composites were prepared using Resin Transfer molding technique by changing filler loading (5, 10, 15, and 20 wt%) for both raw and DWS reinforced UP. Mechanical (tensile and flexural), Fourier transform infrared spectroscopy (FTIR), morphological (scanning electron microscopy [SEM]) and thermal (thermogravimetric analysis [TGA]) properties were successively characterized. FTIR confirmed the removal of lignin from wood sawdust during the delignification process. The tensile strength, Young's modulus, and flexural strength values increased only up to 15% filler loading then decreased with increasing the filler. DWS reinforced composites had better mechanical properties compared to raw composites. SEM micrographs reveal that DWS reinforced composites have good compatibility with UP resin. According to TGA results, DWS reinforced composites showed enhanced thermal stability at the final decomposition stage above 400°C. J. VINYL ADDIT. TECHNOL., 24:185–191, 2018. © 2016 Society of Plastics Engineers     

Thermal and mechanical properties of functionalized mullite reinforced unsaturated polyester composites

This work studies the development of varying weight percentages (0.5, 1.0, and 1.5 wt%) of surface functionalized mullite reinforced unsaturated polyester (UP) composites and their thermal, dielectric, water absorption, and mechanical properties. The synthesized mullite was functionalized with vinyltriethoxysilane (VTES). The introduction of vinyl groups on the surface of mullite was confirmed by FT‐IR, TGA, and X‐ray diffraction (XRD) analyses. Varying weight percentages (0.5, 1.0 and 1.5 wt%) of vinyl functionalized mullite (VFM) were incorporated into UP resin with a benzoyl peroxide initiator to obtain composites. The resultant data obtained from thermal, mechanical, dielectric, and water absorption studies, indicate that incorporation of VFM, leads to a significant improvement in the thermo mechanical, dielectric, and moisture resistant properties of the UP composites, compared with those of neat UP matrices. The molecular dispersion of VFM fiber in reinforced UP matrix composites was confirmed by SEM analysis. POLYM. COMPOS., 35:1663–1670, 2014. © 2013 Society of Plastics Engineers     

Fracture toughness of particle filled fiber reinforced polyester composites

Fracture behavior of polyester composite systems, polyester mortar and glass fiber reinforced polyester mortar, was investigated in mode I fracture using single edge notched beams with varying notch depth. The beams were loaded in four-point bending. Influence of polymer content on the flexural and fracture behavior of polyester composites at room temperature was studied using a uniform Ottawa 20–30 sand. The polymer content was varied between 10 and 18% of the total weight of the composite. The flexural strength of the polyester mortar systems increase with increase in polymer content while the flexural modulus goes through a maximum. The critical stress intensity factor (K_IC) for the optimum polyester mortar (14%) was determined by two methods including a method based on crack mouth opening displacement. The K_IC for polyester mortar is linearly related to the flexural strength. Polyester mortar (18%) reinforced with 4% glass fibers was also investigated, and crack growth resistance curve (K_R) was developed with crack extension (Δa). A model has been proposed to represent the fracture toughness with change in crack length, K_R - Δa relationship, of fiber reinforced polyester composite.     

Diffusion of seawater in unsaturated polyester resin and its glass fiber reinforced composites in the presence of titanium dioxide as UV absorber

Diffusion of seawater in unsaturated polyester resin (UPR) and its glass fiber reinforced composite in the presence of titanium dioxide has been studied by sorption method. Incorporation of glass and TiO₂ to UPR alters the seawater diffusion process from Fickian to non‐Fickian type. The dual mode sorption model is used to separate Fickian‐controlled and relaxation‐controlled diffusion in case of UPR‐T, UPR‐G, and UPR‐GT. The presence of TiO₂ seems to stabilize UPR and its glass reinforced samples but an increase in the rate of seawater diffusion is observed for these systems. The free volume determined from positron lifetime measurements support the diffusion data in these systems. Results further indicate that the contribution to diffusion in the later stages of sorption is due to the increased contribution from the interfaces. The plasticizing effect of TiO₂ is clearly seen even in the glass reinforced composite. DMA results show an increase in flexibility because of TiO₂ presence both in the neat as well as glass reinforced resin which is well supported by decrease in T_g value from DSC data. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2784–2794, 2006     

Toughening mechanisms in rubber-modified glass fiber/unsaturated polyester composites

An important case of composite failure is the leakage of pipes and pressure vessels subjected to internal pressure. The primary damage mechanism leading to leakage is transverse cracking parallel to the fibers. Effects of matrix toughening on transverse cracking strains were therefore investigated for GF/UP cross-ply laminates with matrices of different liquid rubber content. The strain to the first transverse crack was increased from 0.2 to 0.6% with 10 wt% rubber. Debonding occurred at similar strains in GF/UP and GF/UP-rubber. However, whereas debonding was almost simultaneous with transverse cracking in GF/UP, gradual growth of debonds to short cracks took place initially in GF/UP-rubber. This was followed by slow extension of short cracks to a critical flaw size corresponding to unstable growth.     

Polyisobutylene-based modifiers for glass fiber reinforced unsaturated polyesters composites

In order to improve the toughness of glass fiber (GF) reinforced unsaturated polyester resin (UPR), low molecular weight polyisobutylene (LPIB) was selected as the toughening agent. Considering its poor thermal compatibility with UPR matrix, LPIB was first grafted by two small molecular compounds, named maleic anhydride (MAH) and glycidyl methacrylate (GMA) through the novel solvothermal method which was developed in our laboratory. And then, all of these three kinds of low modulus elastomers, including LPIB, MAH grafted polyisobutylene (LPIB-g-MAH) and GMA grafted polyisobutylene (LPIB-g-GMA) were selected to modify GF reinforced UPR (GFRUP) composites. According to the results, incorporation of small amounts of grafted LPIB contributed greatly to the improvement of the toughness of GFRUP composites because of the high flexibility of the molecular chain without obviously influencing other primary properties. Moreover, 4?wt% of elastomer was an optimal amount for promoting the mechanical properties of GFRUP composite. Compared to other liquid rubbers, LPIB-g-GMA had the best toughening effect due to its stronger effect of GMA on UPRGF system. In addition, the impact strength of the modified GFRUP composite was improved up to 2.3 order of that of the unmodified GFRUP composites when 4?wt% LPIB-g-GMA was added. Consequently, LPIB-g-GMA could be employed as an effective toughening agent to GFRUP system. The toughening mechanism, thermal behavior, thermal stability and morphology of GFRUP composite are also discussed. The morphology analysis further proved the increase in toughness through the addition of grafted LPIB.     

Carbon nanofibers for strain and impact damage sensing in glass fiber reinforced composites based on an unsaturated polyester resin

In this article, a successful employment of carbon nanofibers (CNFs) as a filler in the unsaturated polyester (UP) matrix of a glass fiber reinforced polymer (GFRP) is reported. Because of the high aspect ratio of carbon nanofibers, very small amount of these particles were sufficient to significantly modify the electrical properties of the obtained glass fiber composites: for this reason, nanocomposite matrices were produced using no more than 1 wt% of these nanoparticles. The goal of this work was to investigate the possibility to correlate the presence of a mechanical stress, or the onset of damage, in the composite produced, with the variation of electrical resistance. Following this goal, the electrical resistance of the samples was constantly measured during their mechanical testing. Two different kinds of load were applied: flexural and impact. It was possible to show that a systematic variation in the electrical resistance of the composite takes place in correspondence of both the growth of a flexural state of stress, and the creation of an impact damage. In the case of the flexural load, the electrical resistance versus strain curves provides information on the growth of damage well before such damage affects the stress–strain curve. In the case of the impact damage, electric resistance measurements were able to monitor the loss of mechanical integrity before the complete failure. SEM pictures of the crack surface have confirmed the role of the carbon nanofibers in the sensing process. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

表面处理对剑麻纤维布/不饱和树脂材料性能影响

采用碱、高锰酸钾及热对剑麻纤维布进行了表面处理,并由真空辅助树脂传递模塑成型(VARTM)工艺制备了剑麻纤维布增强不饱和聚酯树脂复合材料。通过对复合材料的力学性能及吸水性的测试,研究了不同剑麻纤维布表面处理对其不饱和聚酯树脂复合材料性能的影响。结果表明:经过碱处理,复合材料的拉伸、弯曲,冲击强度提高最大,可分别提高26.5%,16.5%和22.6%,吸水率降低了47.5%。对剑麻纤维布进行表面处理可使复合材料的界面性能得到改善,力学性能提高,吸水性降低。     

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     

Approaches to improve the properties of wood fiber reinforced cementitious composites

In an attempt to improve the workability, stability, and physical and mechanical properties of wood fiber-reinforced cementitious composites (WFRCs), alkali-activated blended cements have been explored for their compatibility with various wood fibers such as hardwood fiber, recycled newspaper fiber and recycled kraft paper fiber. Methods including high shear mixing, modifying the cement matrix with silica fume, and molding pressure were evaluated as means for further strengthening the wood fiber-reinforced cement composites. Flexural strengths up to 40 MPa. along with enhanced toughness have been achieved.     

Mechanical properties of carbon fiber reinforced polyester/urethane hybrid network composites

Hybrid resins of unsaturated polyester/urethane were synthesized and characterized. Both the toughness and stiffness of the polyester were improved significantly by incorporating 20 wt% urethane. Unsaturated polyester, styrene, and ethane showed good compatibility during blending and probably formed a simultaneous interpenetrating network (IPN) during polymerization. The resultant IPN morphology possessed a unique glass transition temperature. This IPN morphology not only imparted great fracture resistance to the otherwise brittle polyester, but also changed the fracture mode of new resin composites. The molecular weight of unsaturated polyesters did not have significant effect on the mechanical properties, but did exert an apparent influence on the fracture mode. During the cure process the side reaction, an amine reaction, could be suppressed addition of suitable promoter and catalyst.     

Investigation of unsaturated polyester composites reinforced by aspen high‐yield pulp fibers

Aspen chemithermomechanical pulp fiber‐reinforced unsaturated polyester (UPE) composites were fabricated using premade paper handsheets. The effects of handsheet wet‐pressing pressure, grammage, and subsequent fabrication methods on the composite properties were evaluated. The composites obtained using the optimum process parameters had tensile moduli and tensile strengths comparable with those of traditional glass fiber‐reinforced UPE composites. The pressed composites had very consistent tensile moduli that were well fitted by the Halpin–Tsai and Tsai–Pagano models. The classical Kelly‐Tyson and Bowyer‐Bader models significantly underestimated the composite tensile strengths and the potential reasons for this discrepancy are discussed. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Fabrication and characterization of novel zirconia filled glass fiber reinforced polyester hybrid composites

Novel hybrid glass fiber reinforced polyester composites (GFRPCs) filled with 1‐5 wt % microsized zirconia (ZrO₂) particles, were fabricated by hand lay‐up process followed by compression molding and evaluated their physical, mechanical and thermal behaviors. The consumption of styrene in cured GFRPCs was confirmed by Fourier transform infrared spectroscopy. The potential implementation of ZrO₂ particles lessened the void contents marginally and substantially enhanced the mechanical and thermal properties in the resultant hybrid composites. The GFRPCs filled with 4 wt % ZrO₂ illustrated noteworthy improvement in tensile strength (66.672 MPa) and flexural strength (67.890 MPa) while with 5 wt % ZrO₂ showed 63.93% rise in hardness, respectively, as compared to unfilled GFRPCs. Physical nature of polyester matrix for composites and an improved glass transition temperature (T_g) from 103 to 112 °C was perceived by differential scanning calorimetry thermograms. Thermogravimetric analysis revealed that the thermal stability of GFRPCs was remarkably augmented with the addition of ZrO₂. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43615.     

Mechanical properties of woodflour unsaturated polyester composites

Agrowastes and woodflour are a potential and attractive alternative of cheap reinforcement for brittle polymeric materials because they can reduce costs and, at the same time, improve certain properties. On the other hand, their high moisture sorption and low microbial resistance are disadvantages that need to be considered and, as far as possible, corrected. Polyester resins are widely used throughout the world, and can be processed with reinforcing agents very easily. In this work, the effect of the addition of chemically modified woodflour on the final properties of unsaturated polyester composites was studied. The filler was treated with an alkaline solution to increase its interfacial area and then modified with maleic anhydride (MAN) under severe reaction conditions (140°C, 24 h). No improvement in the mechanical behavior of polyester–woodflour composites was found when particles were only alkali treated, while the composites prepared with MAN-treated woodflour offered better performance under compressive loads. Simple mechanical models used to fit the experimental flexural behavior indicated that a good compatibility between filler and matrix was obtained regardless of the kind (treated or untreated) of reinforcement used. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2121–2131, 1998     

Mechanical and tribological behavior of alumina and alumina‐CNT reinforced hybrid unsaturated polyester composites

Micro‐ and nano‐scale wear behavior of alumina vis‐á‐vis alumina‐carbon nanotube‐reinforced hybrid composites has been studied. In comparison to the pristine alumina, the alumina‐carbon nanotube hybrid reinforcement resulted in reduced scratch depth and lower frictional coefficient. Addition of carbon nanotube has effectively modified the pristine alumina into a superior wear resistant filler. POLYM. COMPOS., 37:1577–1586, 2016. © 2014 Society of Plastics Engineers