Biodegradable composites: Morphological,chemical, thermal,and mechanical properties of composites of poly(hydroxybutyrate‐co‐hydroxyvalerate) with curaua fibers after exposure to simulated soil

Composites produced from biodegradable polymeric matrixes reinforced with vegetable fibers have attractive mechanical properties and are environmentally friendly. This work is directed to the biodegradation of a composite made of a poly(hydroxybutyrate‐co‐hydroxyvalerate) matrix reinforced with curaua fibers (with and without alkaline treatment) in simulated soil. The composites were developed by extrusion and injection and were later buried in simulated soil according to the ASTM G160‐03 method. Scanning electron microscopy showed evidence of microbial attack on the samples surfaces. Infrared spectra showed that the composites biodegradation was mainly caused by erosion of the surface layer resulting from microorganisms activity. Thermogravimetric analysis pointed out reduced thermal stability of the samples, and results of differential scanning calorimetry showed that the degree of crystallinity increases and then decreases progressively throughout the degradation period, indicating that enzymatic degradation primarily occurs in the amorphous phase material and thereafter in the crystalline phase. For curaua composite fibers, reductions in tensile strength and elastic modulus are more significant, indicating that the presence of fibers promotes biodegradation of the curaua fiber. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40712.     

Characterization of composites based on recycled expanded polystyrene reinforced with curaua fibers

This study evaluated the mechanical, thermal, rheological, and morphological properties of virgin and recycled matrices and their composites with 20 wt % of curaua fiber. The recycling process of postconsumer polystyrene was carried out by grinding and extrusion. It was found that the recycling of expanded polystyrene did not have a major influence on the mechanical properties; however, the thermal stability was increased. The addition of curaua fibers led to increases in the tensile strength, modulus of elasticity, rigidity, thermal stability and melt viscosity of the composites. The composites made with the recycled matrix revealed higher thermal stability and melt viscosity than those made with the virgin matrix. Scanning electron microscopy characterization showed empty spaces where the curaua fibers had pulled out of the matrices in the fractured regions, indicating poor interfacial adhesion without the use of a coupling agent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

竹纤维/MUF复合材料的老化性能研究

以质量损失率、机械强度、羰基指数及乙烯基指数的变化作为综合指标,采用紫外光加速老化试验研究纳米SiO2和纳米TiO2对竹纤维(BF)/三聚氰胺-甲醛-尿素(MUF)复合材料紫外光老化性能的影响。结果表明,随着紫外光老化时间的延长,竹纤维/MUF复合材料的质量损失率、羰基指数和乙烯基指数增加,弯曲强度和冲击强度下降;纳米SiO2和纳米TiO2对竹纤维/MUF复合材料的紫外老化有一定的延缓作用。     

Composites based on renewable materials: Polyurethane‐type matrices from forest byproduct/vegetable oil and reinforced with lignocellulosic fibers

The use of products and byproducts from the agro‐industry and forest biorefinery is essential for the development of value‐added and low environmental‐impact materials. In this study, polyurethanes were prepared using sodium lignosulfonate (NaLS) and castor oil (CO) as reagents and were used to prepare composites reinforced with lignocellulosic fibers, namely, curaua and coir fibers (30 wt %, 3 cm length, and randomly oriented). The SEM images of fractured surfaces of the composites revealed excellent adhesion at the fiber/matrix interface of both coir and curaua composites, which probably resulted from the favorable interactions between polar groups, as well as amid low polarity domains that are present in both the matrix and the reinforcements. The composites exhibited different impact/flexural and strength/flexural moduli (NaLS/CO/Curaua = 465 Jm^?1/44 MPa/2 GPa; NaLS/CO/Coir = 180 Jm^?1/25 MPa/1 GPa). The higher tensile strength/aspect ratio of the curaua fibers (485 MPa/259) compared with that of the coir fibers (120 MPa/130) most likely contributes to the enhanced performance of its composite. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical behavior and correlation between dynamic fragility and dynamic mechanical properties of curaua fiber composites

In this study, the mechanical properties and physical–chemical characteristics of curaua composites were evaluated using tensile and short beam testing and dynamic mechanical analysis. Curaua/polyester composites with different pretreatment (washing and drying), fiber length (10–50 mm) and fiber volume fraction (%V_f) (11, 22, and 38 vol%) were studied. The results show that the composites produced using 50 mm long washed/dried fibers and %V_f of 38 vol% achieved better mechanical properties, such as tensile strength and modulus and short beam strength. Fragility index “m” of the composites increased upon curaua incorporation, which may be attributed to a reduction in polyester chemical interactions (due to fiber dwelling of the polyester network). The energy required in initiating the cooperative motion at the “ideal” glass transition temperature and the cooperative rearrangement regions (CRR) also increased upon curaua incorporation, since CRR is considered the subsystem of the sample and for higher fiber content the greater the molecular heterogeneity. Finally, the Angell fragility concept was successfully applied to polymer composite systems. POLYM. COMPOS., 35:1078–1086, 2014. © 2013 Society of Plastics Engineers     

Plant oil‐based biofoam composites with balanced performance

BACKGROUND: Biofoam composites were prepared using short sisal fibers as reinforcement and acrylated epoxidized soybean oil as matrix, aiming at replacing traditional unsaturated polyester foams in structural applications. The compressive properties of the composites were examined as a function of fiber loading, fiber length and foam density. RESULTS: The foam composite with 10 phr (parts per hundred of base resin by weight) sisal fiber possessed properties similar to those of commercial unsaturated polyester foams. A study of the failure mechanism revealed that debonding between fiber and matrix was a key issue responsible for catastrophic damage of the composites. According to this finding, surface pre‐treatment of the sisal using an alkali or silane coupling agent was carried out. This brought about positive effects on interfacial interaction and compressive strength of the composites, as desired. Also, soil burial tests proved that the foam composites could be biodegraded, and the incorporated sisal fibers accelerated the biodegradation of the composites. CONCLUSION: This work shows the feasibility of making rigid biofoams from natural resources, which could be potential candidates for structural foams. Copyright © 2009 Society of Chemical Industry     

Influence of the coupling agent on the mechanical properties of SiCf/poly(phenylene benzobisoxazole) composites

Poly(phenylene benzobisoxazole) (PBO) was first used as matrix to fabricate the two‐dimensional SiC_f/PBO composites by a lamination method. Different amounts of coupling agent were introduced to improve the bonding between silicon carbide (SiC) fibers and the PBO matrix during the fabrication of the SiC_f/PBO composites. The surface structure and composition of the as‐received PBO and PBO treated with the coupling agent were analyzed, and the morphology and flexural strength of the composites were characterized. The Fourier transform infrared analysis indicated that the hydroxyl groups from the coupling agent were successfully introduced to PBO. The flexural strength of the composites increased at first with increasing content of the coupling agent but decreased with excessive addition of the coupling agent. The flexural strength of the composites was improved from 15 to 89 MPa. The test results suggested that the interaction between the SiC fiber and the treated PBO with the coupling agent was intensified. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39805.     

自制光稳定剂HWPAN-g-TiO2与几种光稳定剂对聚丙烯性能的对比研究

利用废旧腈纶织物制备了一种聚丙烯（PP）用大分子紫外屏蔽吸收类型光稳定剂,利用其和通用的受阻酚类光稳定剂分别制备耐候性PP复合材料,并进行了人工加速老化实验。探究了大分子紫外屏蔽吸收类型光稳定剂在PP老化过程中对PP老化降解的影响,并与通用的受阻酚类光稳定剂进行了对比研究。结果表明,大分子紫外屏蔽吸收类型光稳定剂效果明显,在人工加速老化500 h之后,PP的羰基指数高达150.3;而PP/HWPAN-g-TiO2仅为53,与此同时,PP的拉伸强度从25 MPa降至6.9 MPa,下降了72.4 %;而PP/HWPAN-g-TiO2的拉伸强度从29 MPa降至25 MPa,下降13.8 %。     

Curaua leaf fiber (Ananas comosus var. erectifolius) reinforcing poly(lactic acid) biocomposites: Formulation and performance

Formulations of poly(lactic acid) (PLA) reinforced by curaua leaf fibers were prepared and characterized. This biocomposite has material characteristics such as biodegradability and renewability. This work aimed to develop a PLA/curaua leaf fiber composite as a sustainable biodegradable polymer composite. The PLA and composites were thermally, mechanically, and morphologically evaluated. The critical fiber length was studied to check its influence on the mechanical properties. Predictions of the Young's modulus were done to compare with the experimental data, having a reasonable agreement. The Young's modulus increased above 70%, and the impact strength increased 20% compared with the pure PLA. Thermal analysis showed that formulations with up to 20% by weight of fibers were more thermally stable. The fiber modified the crystallinity of the PLA matrix. The best overall balance of properties was attained in composites containing 15% curaua fiber. POLYM. COMPOS., 36:1520–1530, 2015. © 2014 Society of Plastics Engineers     

The influence of alkaline treatment on the mechanical performance of geopolymer composites reinforced with Brazilian malva and curaua fibers

Lignocellulosic fibers obtained from the curaua (Ananas erectifolius) and malva (Malva sylvestris) plants in Brazil can be used as suitable reinforcements for geopolymers (GPs) owing to their high strength, ready regional availability, and low cost. In this work, the tensile and flexural strengths of untreated and NaOH alkali-treated curaua and malva fiber-reinforced GP composites were measured according to ASTM standards. Curaua reinforced GP composites had an average tensile strength of 25.7 (±) 7.1 MPa and flexural strength of 18.9 (±) 4.72 MPa. Malva GP composites withstood 19.18 (±) 9.0 MPa in tension and 31.5 (±) 7.6 MPa in flexure. Additionally, pullout tests were performed to investigate the debonding mechanisms for both fibers, with and without alkaline treatment, finding increases in chemical bonding for the treated samples due to roughness enhancements through fiber surface modifications with alkali treatment. Thermogravimetric analysis and X-ray diffraction were used to characterize the physical fiber modifications after alkali treatment, evidencing lignin and hemicellulose removals. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to further examine the fiber–matrix interaction, with proofs of interfacial tailoring.     

香蕉纤维的表面改性及其增强环氧树脂复合材料的性能研究

采用硅烷偶联剂(A-174)偶联、高锰酸钾接枝和乙酰化包覆等3种方法对香蕉纤维进行表面改性,制备了改性香蕉纤维增强环氧树脂复合材料,测试其拉伸、弯曲、压缩、冲击等力学性能。结果表明,偶联、接枝、包覆等表面改性均能明显改善香蕉纤维与基体树脂的相容性,提高复合材料的力学性能,其中偶联改性的效果最好。当改性香蕉纤维含量为10wt%时,与未改性的香蕉纤维比较,复合材料的拉伸强度、弯曲强度、压缩强度分别提高了1.8、1.0、2.6倍;随着纤维含量的增加,复合材料的力学性能明显提高。     

Optimal performances of ultrasound treated kenaf fiber reinforced recycled polypropylene composites as demonstrated by response surface method

Kenaf fiber (KF) reinforced recycled polypropylene (RPP) composites were produced by melt cast method. To improve interfacial adhesion between fiber and RPP matrix, fiber surface modification was carried out by means of ultrasound treatment. Maleic anhydride grafted polypropylene (MAPP) was used as a coupling agent. Composites were examined by mechanical test, melt flow indexing test, scanning electron microscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Water uptake analysis and accelerated weathering test were carried out to find the suitability of the composites in outdoor application. Among the raw fiber contents ranging 10?50 wt % in the composites, the maximum tensile strength (TS) was observed at 40 wt % KF loading without using MAPP. Treated KF‐based composite with MAPP promotes this maximum TS value, which is 57% higher than that of raw KF‐based composite. TGA and DSC analyses exhibit an enhancement of thermal stability in treated KF‐reinforced RPP composites with MAPP. Incorporation of MAPP in the composites shows higher activation energy, suggesting improved interfacial bonding between fibers and matrix. Response surface method was employed to demonstrate the optimal treatment parameters for TS, showing excellent agreement with the observed values. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Studies on mechanical properties of polyethylene–organic fiber composites. I. Nut shell flour

Composites were made from polyethylene and an organic fiber (pecan shell and peanut hull flour) using a compression-molding technique. Studies of variations in molding temperature (145–180°C), fiber concentration (0–40% by weight), and fiber mesh size (100, 200, and 325) were correlated to the mechanical properties of the composites (tensile strength, elongation, fracture energy, modulus, and impact strength). In untreated nut shell composites, tensile strength decreased steadily as the fiber concentration increased. This was due to poor bonding between the untreated fiber and polymer. Polyisocyanate was used as a coupling agent and its effect on mechanical properties of the composites was studied. Significant improvement in tensile strength was achieved with an isocyanate coupling agent, but it had no effect on modulus of the composites. Both untreated and isocyanate-treated composites had lower impact strength values; further composite matrix modifications would be necessary to maintain or improve impact strength.     

Development of basalt fiber‐reinforced thermoplastic composites and effect of PE‐g‐MA on composites

The thermoplastic matrix composites have gained great importance in last three decades. The chopped basalt fiber (mineral fiber) is considered to be a good fiber due to excellent properties as potential reinforcement of composite materials. In this work, composites of chopped basalt fiber (6 mm) with thermoplastic material Nylon‐6 (Polyamide‐6) were prepared and its mechanical and morphological properties were evaluated for automobile applications. The melt blending was carried out in corotating twin‐screw extruder and injection‐molded test samples were prepared for the analysis. The test samples of composite without coupling agent prepared by varying the loading of basalt fiber content of 5%, 10%, 15%, 20%, and 25% by weight and with coupling agent composite loading of Nylon‐6 and basalt fiber content were kept constant and the coupling agent (PE‐g‐MA) loading were changed as 1, 2, 3, 4, and 5 phr. The Mechanical and SEM properties were evaluated. From the test results, it was observed that the mechanical properties were improved with increasing coupling agent ratio. SEM images show good dispersion and adhesion of matrix and reinforcement. POLYM. COMPOS., 38:2798–2805, 2017. © 2015 Society of Plastics Engineers     

Promising curaua fiber‐reinforced polyester composite for high‐impact ballistic multilayered armor

A typical multilayered armor system (MAS) is composed of a harder front ceramic tile, which is able to erode heavy ammunition, such as the 7.62 mm bullet, followed by a second layer to further reduce the impact energy. Aramid fabric is a common choice for the second layer. In the present work, polyester matrix composites reinforced with 10 to 30 vol% of curaua fibers, despite having much lower strength and stiffness than aramid fabric, displayed similar trauma indentation in a standard clay witness simulating the human body. Impedance matching and scanning electron microscopy analyses suggest effective energy absorption through ceramic fragment capture by curaua composites. Additionally, because of the high cost of aramid fabric, a full MAS with curaua fiber composite is much cheaper than a MAS composed of aramid fabric. Taking into consideration, both the economical and environmental advantages of natural fibers, it is concluded that curaua fiber‐reinforced polyester composite could replace aramid fabric as the second layer in MASs for personal ballistic protection. POLYM. ENG. SCI., 57:947–954, 2017. © 2016 Society of Plastics Engineers     

Abiotic and biotic degradation of post‐consumer polypropylene/ethylene vinyl acetate: Wood flour composites exposed to natural weathering

The effects of natural weathering on the visual appearance and chemical changes of wood plastic composite (WPC) formulations based on post‐consumer polypropylene/ethylene vinyl acetate (PP‐EVA) matrix were investigated. The WPC composition used was 70/30 (w/w) (recycled PP‐EVA/wood flour). Besides, the effectiveness of using coupling agent on adhesion of WPC and its influence in degradation were evaluated. Colorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy, mechanical test, and biodegradation in simulated soil after natural weathering were used in this research. The results showed the samples with longer exposure time to natural weathering presented significant color change, increased in carbonyl index, and wood loss on weathered WPC surfaces. Weathered WPC exhibited decreased in mechanical properties, higher mass loss after biodegradation test when compared with no weathering WPC, reaching to 15.0% mass loss against 3.7%, respectively. Climatic conditions directly affect the characteristics of all composites, thus indicating a significant photo‐oxidation of the samples with a longer time of exposure to weathering, and this natural ageing has facilitated the WPC biodegradation . POLYM. COMPOS., 38:571–582, 2017. © 2015 Society of Plastics Engineers     

Poly(lactic acid)/pulp fiber composites: The effect of fiber surface modification and hydrothermal aging on viscoelastic and strength properties

Poly(lactic acid) (PLA)/kraft pulp fiber (30 wt%) composites were prepared with and without a coupling agent (epoxidized linseed oil, ELO, 1.5 wt%) by injection molding. The non-annealed composite samples, along with lean PLA, were exposed to two hydro-thermal conditions: cyclic 50% RH/90% RH at 23 and 50°C, both up to 42 days. The aging effects were observed by size exclusion chromatography, differential scanning calorimetry, dynamic and tensile mechanical analysis, and fracture surface imaging. ELO temporarily accelerated the material's internal transition from viscous to an increasingly elastic response during the aging at 50°C. ELO also slowed down the tensile strength reduction of the composites at 50°C. These observations were explained with the hydrophobic ELO molecules' coupling and plasticizing effects at fiber/matrix interfaces. No effects were observed at 23°C.     

超高分子质量聚乙烯纤维黏结强度增强方法研究

为提高超高分子质量聚乙烯(UHMWPE)纤维复合材料中纤维与树脂基体之间的界面黏结强度,提出通过不同质量分数的硅烷偶联剂KH-570处理纳米SiO_2对UHMWPE纤维进行表面改性。对改性处理后的纤维与乙烯基酯树脂进行黏结强度试验,发现硅烷偶联剂处理纳米SiO_2能有效提高纤维的界面黏结强度,同时使纤维保持一定的断裂强度。     

Grafting acrylate functionalities at the surface of carbon fibers to improve adhesion strength in carbon fiber–acrylate composites cured by electron beam

Acrylate functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix cured by electron beam. An isocyanate bearing aliphatic urethane acrylate was used as a coupling agent. As revealed by X-ray photoelectron spectroscopy, the isocyanate groups reacted with carboxylic acids and hydroxyl groups located at the surface of the fiber, leading to a covalent bonding of the acrylate groups. The adhesion strength was measured by a micromechanical test derived from the pull-out test. A significant improvement of the interfacial shear strength was obtained (+91%) with an electron beam curing. For comparison, an isothermal cure by UV was also investigated and led to the same level of adhesion strength. The improvement was also proved by an increase in the 90° flexural strength of unidirectional composites (+38%). Grafting functionalities that were compatible with the radical mechanism of the polymerization of the matrix appeared to be a promising strategy for the improvement of the mechanical properties of carbon fiber–acrylate composites cured by electron beam.     

Photoaging and stabilization of rigid PVC/wood‐fiber composites

Ultraviolet (UV) weathering performance of unpigmented and rutile titanium dioxide pigmented rigid polyvinyl chloride (PVC)/wood‐fiber composites has been studied. The composite samples were manufactured by dry‐blending PVC, wood fibers, and other processing additives in a high‐intensity mixer. The dry‐blended compounds were extruded and compression molded into panel samples. The manufactured samples were artificially weathered using laboratory accelerated UV tests. Composite samples were exposed to 340‐nm fluorescent UV lamps and assessed every 200 h, for a total of 1200 h of accelerated weathering. Each assessment consisted of a visual examination of surface roughness or erosion, a contact angle measurement, a FTIR collection, and a color measurement. The experimental results indicated that wood fibers are effective sensitizers and that their incorporation into a rigid PVC matrix has a deleterious effect on the ability of the matrix to resist degradation caused ultraviolet irradiation. The light stability of these composites could be improved quite efficiently with the addition of rutile titanium dioxide photoactive pigment during formulation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1943–1950, 2001