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Abstract
The effect of fiber surface modification on the fatigue strength of a glass fiber reinforced polyamide-6 has been investigated. Tension axial fatigue tests were conducted with specimens extracted from injection moulded plates. Results show the variation of the fatigue strength as a function of the fiber concentration. The experimental data, the tensile tests have shown the effective improvement of interfacial adhesion between the fiber surface and the matrix.
... In the next step, the cementing molecules (lignin and hemicellulose) should be removed, as the presence of these molecules can interfere with the crystallinity of the cellulose fibers [7]. Hemicellulose and lignin tend to reduce the crystallinity ratio, thermal stability and other mechanical properties [8]. The purification techniques remove the hemicellulose and lignin, as well as prevent moisture absorption and improve the surface properties of the extracted fiber [9]. ...
This study explores the possibility of using Water lettuce (Pistia stratiotes) as a cost-effective substrate for the commercial extraction of cellulose biopolymer using a wide variety of physicochemical treatment methods to compare their efficiency in cellulose extraction. The extraction of cellulose from water lettuce, although promising due to their high cellulose content, was less explored as per the available literature. In this study, functional properties like bulk density-packed density, hydrated density, water retention capacity, oil retention capacity, emulsifying activity and setting volume of the extracted cellulose were studied. The cellulose content from water lettuce was found to be 38.94 ± 0.10% by anthrone method. Preliminary confirmation of cellulose biopolymer was done using the study of functional groups using Fourier Transform Infrared (FT-IR) analysis. Further characterization studies like Scanning Electron Microscopy (SEM), X- Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to understand the molecular architecture and purity of the cellulose extracted. Fabrication of cellulose sheets was carried out using starch as the plasticizer. Biodegradation studies were conducted in garden soil for four weeks and a high degradation rate of 78.22 ± 0.71% was observed in the fourth week of soil burial.
... Nevertheless, the high melt viscosity of PAs together with the chemical inertness of most of these reinforcing elements result in poor matrix-filler interactions that, in turn, are responsible for the performance impairment of the composites [22]. Therefore, surface modification of fibers and/or the use of coupling agents are usually required to enhance the overall performance [18,23,24]. In addition, melt grafting of fillers onto polymers is an effective method to achieve compatibilization and, thus, enhance the mechanical strength of composites [25]. ...
Fully bio-based polyamide 1010 (PA1010) was melt-compounded with 15 wt% of slate fibers (SFs), which were obtained from wastes of the tile industry, and the resultant composites were shaped into parts by injection molding. The as-received fibers were first thermally treated and afterwards subjected to surface modification with glycidyl- and amino-silane coupling agents to improve the interfacial adhesion of the composites. The incorporation of both the glycidyl-silane slate fiber (G-SF) and amino-silane slate fiber (A-SF) remarkably improved the mechanical strength of PA1010, inducing a 3-fold increase in tensile modulus. The composite parts prepared with the silanized SFs also presented higher thermal stability and improved thermomechanical resistance. Water uptake was reduced below 1 wt%, encouragingly suggesting that the mechanical performance of the PA1010/SF composites would be scarcely affected by atmospheric humidity. G-SF was the most effective in strengthening PA1010. This improvement was ascribed to the higher reactivity of the cyclic anhydride in the coupled silane with the terminal hydroxyl groups of the biopolymer.
The mechanical properties and phase microstructure of ternary phase polypropylene composites have been investigated using combinations of rigid glass beads and ethylene/propylene rubber (EPR) modifiers. Particular consideration has been given to the relative interaction between these components and their dispersion within the composite. In this regard, EPR and untreated glass beads existed as independent phases, whereas EPR functionalized with maleic anhydride showed a tendency to encapsulate the inorganic phase. As a consequence, marked differences in mechanical properties, in particular toughness, were exhibited by these systems, manifested by changes in failure mechanism. Structure in these composites was explored by Fourier transform infrared spectroscopy, dynamic mechanical analysis, and scanning electron microscopy. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 587–597, 1998
Short glass fiber (SGF) reinforced polypropylene composites toughened with styrene-ethylene-butylene-styrene (SEBS) triblock copolymer were injection molded. The effect of maleic anhydride (MA) functional group on the mechanical performance of the hybrid composites was investigated. In this study, MA was either grafted to PP (PP-g-MA) or SEBS copolymer (SEBS-g-MA). The mPP blend was prepared by compounding 95% PP with 5% PP-g-MA. The matrix of hybrid composites consists of either SEBS/mPP or SEBS-g-MA/mPP. Tensile tests showed that SGF exhibits a beneficial effect for restoring the stiffness of the SEBS/mPP blend. Impact measurements on SEBS/mPP exhibited superior impact strength. However, the incorporation of SGF into SEBS/mPP and SEBS-g-MA/mPP blends reduced the impact strength considerably. SEM observations revealed that the SGF surfaces of both SGF/SEBS/mPP and SGF/SEBS-g-MA/mPP hybrids are coated with a thin layer of matrix material. This implied that the MA functional group of mPP improves the adhesion between SGF and PP, and between SGF and SEBS. The essential work of fracture (EWF) method revealed that a strong interfacial bonding between SGF and PP is detrimental to the fracture toughness of ternary SGF/SEBS/mPP and SGF/SEBS-g-MA/mPP hybrid composites. Finally, dynamic mechanical analysis showed that SGF increases the storage modulus but decreases the intensity of damping factor for the hybrids.
In this paper unreinforced and long-glass-fibre-reinforced PA66/PP blends with different glass-fibre sizing were studied with respect to their fracture toughness determined by the typical Kc method. The fracture surfaces of these blends were studied by scanning electron microscopy in order to characterize the failure mechanisms. For the unreinforced blends a decrease in fracture toughness was observed when 25 wt% of polyamide (PA) was added to the polypropylene (PP) matrix, compared with the plain PP and PA matrices. On the other hand an increase in fracture toughness was observed when 25 wt% of PP was added to the PA matrix. This was explained by the differences in thermal expansion of PP and PA. The fracture toughness of the long-glass-fibre (LGF) composites were not affected by the glass-fibre sizing up to a PAPP ratio of 5050. After the phase inversion from a continuous PP to a continuous PA phase in the matrix (between PAPP ratios of 5050and7525) the PA glass-fibre sized composite showed higher fracture toughness than the PP sized. This was explained by the change of the fibre-related failure mechanism from frequent fibre pull-out to fibre fracture. In addition the matrix affected the fracture toughness of the PAPP7525 blend with PA glass-fibre sizing in a positive way, resulting in the highest fracture toughness observed in this study.
The recycling of inseparable polymer mixtures usually results in blends with poor mechanical properties. A mixture of PP and PS was taken as a model compound for a recyclate. The effect of adding glass fibers to a mixture of PP/PS (70/30) was studied, with special attention to long glass fiber reinforcement. Test specimens were made in three different ways: by dry blending (direct injection molding), mild compounding with a single screw extruder, and compounding with a twin screw extruder. The fiber concentration was varied from 0 to 30 wt%. The fiber lengths were determined to investigate fiber attrition. The fiber lengths in the samples were 1.09 mm for dry blending, 0.72 mm for single screw compounding, and 0.33 mm for twin screw compounding. The mechanical behavior was studied by unnotched and notched Izod impact and tensile tests. The PP/PS blend had a low fracture strain and low unnotched Izod impact strength compared with a PP homopolymer. With an increasing fiber concentration and fiber length, the modulus, tensile strength, and particularly the impact strength increased. With a 30 wt% glass fiber of the long fiber compound (dry blended), the modulus was raised by a factor of 3.5, the fracture stress by a factor of 2.5 and the unnotched Izod impact strength by a factor of 10. The product quality as judged by the scatter of the data was best for the twin screw compound and poorest for the dry blend. Compounding with a single screw extruder gave fairly constant injection molding product properties, combined with excellent mechanical properties.
Short glass fiber reinforced (SGFR) PA6,6/PP blends with 20 wt% styrene-ethylene/butylene-styrene triblock copolymers (SEBS) grafted with different levels of maleic anhydride (MA) were studied using both the essential work of fracture (EWF) and J-integral fracture toughness techniques. Good linearity was found between the plane strain specific fracture work, Wf, and the ligament length, l, in single-edge notched bend (SENB) specimens. The two fracture mechanics parameters were compared and there was good agreement between the J-integral fracture initiation toughness, JIC, and the specific essential fracture work, WIe. The skin-core morphology characteristic of injection molded short fiber reinforced thermoplastics (SFRT) was also revealed using the EWF approach.
The tensile properties and notched Charpy impact energy of injection-molded rubber-toughened polyamide 6,6/polypropylene (PA6,6/PP) blends reinforced with short glass fibers (SGF) were studied. The glass fiber content was fixed at 40 wt%. The polymer blends containing various PA6,6/PP ratios, plus a mixture of 10 wt% styrene–ethylene–butylene–styrene (SEBS) and 10 wt% maleic anhydride (MA) grafted SEBS (SEBS-g-MA), were formulated. Two types (123D and 146B) of E-glass fibers were used to examine the influences of PA6,6/PP ratio on mean fiber length and critical fiber length (or fiber–matrix interfacial adhesion) and in turn on the mechanical properties. The PA6,6/PP ratio was found to have significant effects on both the mean fiber length and the critical fiber length in the final samples, and then on the mechanical properties. It was shown that the composite strength increased while the elastic modulus decreased with increasing PA6,6/PP ratio. This observation has been explained using the variance of interfacial adhesion and fiber length with the PA 6,6/PP ratio. The tensile failure strains were higher for the glass fiber-reinforced SEBS/SEBS-g-MA toughened blends than for glass fiber-reinforced toughened PA6,6 or PP composites. The notched Charpy impact energy of the reinforced blends at a medium (75/25) PA6,6/PP ratio was exhibited to be higher than for the reinforced rubber-toughened PA6,6 or PP composites. Consequently, it was concluded that control of the PA6,6/PP ratio would be an effective way to produce composites with optimal combination of superior overall mechanical properties.
The influence of weathering on fracture toughness, Jc, yield strength, y, local ultrasonic velocity, VR, and microhardness, Hu, in unreinforced and a short glass-fibre-reinforced polyester-based thermoplastic Xenoy has been investigated. Unreinforced material weathered for 11 months outdoors in Perth, West Australia, exhibited a significant decrease in VR and Jc, whereas little change was shown in y, Hu and the fracture surface morphology. Irradiation for 1000 h by artificial ultraviolet rays upon the unreinforced material caused a considerable increase in Hu and only a slight deterioration in VR of the surface layer. Filling with the short fibres induced an improvement in y and a large reduction in Jc for the unreinforced material. The natural weathering of the reinforced material caused a small reduction in Jc but a large degradation in the slope of the R-curve. It was concluded that the measurement of Jc and the slope of R-curve in combination with VR and Hu was an effective way to study the effects of weathering on engineering plastics. 1998 Chapman & Hall
A comprehensive study was undertaken on the specific role of rubber on toughening when other rigid polymer or non-polymer
phases were present. Nylon 6,6/SAN blends of various SAN concentrations ranging from pure SAN to pure nylon 6,6 were investigated
with and without fibre reinforcements. These results could be compared with the toughness values of unreinforced and fibre-reinforced
nylon 6,6/ABS alloys from a previous study in order to elucidate the role of rubber. Fracture behaviour was investigated rigorously
by characterizing the fracture initiation toughness, JIC, and the steady-state fracture toughness, Jss. These were then related
to the microstructure and failure modes determined by microscopy and fractography methods. It was found that rubber increased
both fracture initiation and propagation toughness in the presence of the rigid phase, while the rigid phase toughened the
alloy only when the rigid phase/matrix interface was strong enough. The role played by glass fibres was found to be critically
related to the fibre/matrix interfacial strength. Toughening was generally observed, both in the presence and absence of rubber,
when the interface was strong. In all cases toughening could be related to the enhancement of plasticity in the crack tip
by the presence of the rubber phase or the reinforcing glass phase.
The deformation behaviour and the fracture resistance of a range of nylon 6,6/ABS alloys of varying composition both with
and without the presence of glass fibres were investigated. The deformation behaviour was characterized by careful measurements
of the volumetric strain during tensile tests in order to understand the relative roles of cavitation and shear yielding in
these materials. The fracture resistance was investigated in detail in the fracture mechanics sense by characterizing the
J-integral fracture initiation toughness. In materials exhibiting stable crack growth, a new parameter, namely, the plateau
value of the J-integral fracture resistance curve, was measured directly and represented the resistance of the material to
stable crack growth. The results showed that the relationship between the deformation behaviour and fracture resistance was
related to the extent of damage that developed in the crack-tip zone. Substantial additional toughening was developed during
the crack extension stage both in the presence and absence of glass fibres. Glass fibres were found to promote shear yielding
and, as a result, enhance both the fracture initiation as well as the fracture propagation resistance of the nylon 6,6/ABS
alloys.
The present thesis investigates the potential of short fiber reinforced thermoplastic blends, a combination of an immiscible polymer blend and a short fiber reinforced composite, to integrate the easy processing solutions available for short fiber reinforced composites with the high mechanical performance of continuous fiber reinforced composites. The focus of the thesis is to develop an understanding of the processes controlling the morphology and the performance of these complex, ternary systems. Depending on the aspect ratio of the filler particles and their compatibility to the polymeric components one can achieve different morphologies, e.g. filler contained within the dispersed phase, within the matrix phase or at the interface between the two phases. If the fibers are sufficiently long and are preferentially wetted by the dispersed phase an effectively continuous network comprised of fibers welded together by the dispersed phase can be created. In such manner a pseudo-continuous fibrous reinforcement is spontaneously formed during the processing step and a composite material with better mechanical performance can be obtained.
Mechanical behaviour and fracture toughness evaluation of maleic anhydride compatibilized short glass fiber/SEBS/polypropylene hybrid composites
- S C Tjong
- S-A Xu
- Rk-Y Li
- Y W Mai