Preparation of acetylcellulose/silica composites by sol-gel method and their mechanical properties

Acetylcellulose (AC)/silica composites were prepared by sol-gel method in an attempt to realize materials with Young's moduli and bending strengths similar to those of cortical bones. Si(OCH₃)₄ (TMOS)-AC-H₂O-HNO₃-tetrahydrofuran-CH₃OC₂H₄OH solutions were allowed to be gelled, where AC/TMOS mole ratios were defined for AC monomers, and the gels were dried at 30–70^∘C to obtain composites. The composites prepared from solutions of mole ratios of AC/TMOS = 0.5 and 1.0 were composed of micrometer-sized particles rich in silica surrounded by the matrix rich in AC. The composites from solutions of AC/TMOS = 2.0, on the other hand, the interface between the particles and the matrix was much less distinct. All the composite samples showed good machinability, which could be cut into 5 mm × 2 mm × 4.4 mm rectangular specimens by an electric saw without cracking or fracture. The specimens were subjected to three-point bending test, where the degree of plastic deformation and the fracture strain increased, and Young's modulus and bending strength decreased with increasing AC/TMOS ratio in the starting solutions. When the gels were dried at higher temperatures, Young's modulus and strength increased. Young's modulus and bending strength could be varied in the range of 1.8–3.9 GPa and 48–100 MPa, respectively, by varying the AC/TMOS ratio in solutions and the drying temperature.     

Dynamic viscoelastic properties of collagen gels in the presence and absence of collagen fibrils

We measured the dynamic viscoelasticities of collagen gels prepared and modified by four different methods: i) collagen gels cross-linked by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) after their preparation, ii) collagen gels cross-linked simultaneously with their preparation, iii) collagen gels irradiated with gamma rays after their preparation, and iv) collagen gels directly formed from an acidic collagen solution by gamma-cross-linking. Dynamic viscoelasticities of all samples were measured using a rheometer before and after heating for 30 min at 80 °C. The collagen gels sequentially cross-linked by 125 mM EDC after preparation and then heated exhibited mechanically strong properties (storage modulus G′, 7010 Pa; loss modulus G″, 288 Pa; Young's modulus E, 0.012 in the rapidly-increasing phase and 0.095 in the moderately-increasing phase; tensile strain, 5.29; tensile stress σ, 0.053). We generally conclude that the G′ value decreases when gels without fibrils are heated. On the other hand, well cross-linked collagen gels with thick fibrils, such as gels sequentially cross-linked with 125 mM EDC after preparation or gamma-cross-linked conventional gels irradiated at 40 kGy, exhibit a distinct increase in G′ value after heating. Those gels also have thick, twisted, or fused fibrils of collagen.     

Formation of calcium deficient HAp/collagen composites by hydrolysis of α-TCP

Bone-like composites containing calcium deficient hydroxyapatite (CDHAp) were formed by the hydrolysis of alpha-tricalcium phosphate (α-TCP) in the presence of type I collagen. CDHAp-collagen composites were synthesized using two techniques. In one technique α-TCP was mixed with non-milled (as-received) collagen prior to the addition of the aqueous solution. In the second, the collagen was milled with α-TCP in heptane at room temperature prior to its conversion to CDHAp. The effect of milling strongly facilitates the formation of CDHAp at physiological temperature. The proportion of milled collagen between 5 and 20 wt% present in the α-TCP/collagen composites has no significant effect on the rate of CDHAp formation. Variations in pH and in calcium and phosphate concentrations were determined as a function of collagen processing and variations specific to the presence of collagen were discerned. Compared to CDHAp or to composites containing non-milled collagen, diametrical and compressive strengths of CDHAp increased in the presence of milled collagen. Lack of collagen dispersion and incomplete formation of CDHAp during 48 h were the bases for reduced strengths of composites containing non-milled collagen.     

Influence of steady shear flow on dynamic viscoelastic properties of un-reinforced and Kevlar,glass fibre reinforced LLDPE

An experimental study was conducted to observe the effects of parallel-superposed flow condition on viscoelastic properties of LLDPE, Kevlar fibre reinforced LLDPE and hybrid of short glass fibre and Kevlar fibre reinforced LLDPE. Parallel-plate rheometer was employed for these tests. Rheological parameters such as loss modulus (G″) and dynamic viscosity (η′) do not vary significantly on superposing steady state shear with oscillatory shear in the studied range of experiment at 185°C in un-reinforced LLDPE. Kevlar fibre reinforced LLDPE and Kevlar/glass fibre reinforced LLDPE showed significant changes in the flow behaviour under various sets of superposed conditions. Storage modulus (G′), andG″ become highly sensitive to low oscillatory angular frequencies (ω) under superposed conditions. These curves show two different regions with increased ω value. At low ω values, parametersG′ andG″ change sharply reaching a certain value, thereafter, changes are moderate with increased ω. In case of η′ a maxima is observed, position of which, depends upon the value of steady shear rate. Maxima shifts towards higher frequencies with the increased steady shear rate.     

Viscoelastic interpretations of erosion performance of short aramid fibre reinforced vinyl ester resin composites

Short aramid fibre reinforced vinyl ester resin based isotropic composites are fabricated with varying fibre weight fractions (20–50 wt%). The composites were evaluated for their erosion performance under a dynamic set of variables such as impingement angle (30°–90°), impact velocity (43–76 m/s), erodent size (250–600 μm) and stand-off distance (55–85 mm) following design of experiments (DOE) based on Taguchi analysis approach. The thermo-mechanical attributes such as storage modulus, loss modulus and damping properties as viscoelastic responses of the composites were investigated in the temperature range of 0–180 °C for their possible interpretations regarding reinforcement efficiency and energy dissipation aspects relevant to erosion process. An interrelation between the full-width half-maxima (FWHM) of loss modulus peak and erosion rate has emerged indicating the erosion to be mainly controlled by the fibre–matrix interfacial characteristics. The eroded surface morphology investigation by scanning electron microscopy (SEM) revealed the nature of wear-craters, material damage mode and other qualitative attributes responsible in facilitating erosion of the composites.     

Composites for bone repair: phosphate glass fibre reinforced PLA with varying fibre architecture

Internal fixation for bone fractures with rigid metallic plates, screws and pins is a proven operative technique. However, refracture’s have been observed after rigid internal fixation with metal plates and plate fixation has been known to cause localised osteopenia under and near the plate. In the present study, resorbable composites comprising a PLA matrix reinforced with iron doped phosphate glass fibres were investigated. Non-woven random mat laminates of approximately 30% and 45% fibre volume fraction (V_f) were produced, along with unidirectional and 0°–90° samples of approximately 20% V_f. The non-woven composite laminates achieved maximum values of 10 GPa modulus and 120 MPa strength. The 0–90o samples showed unexpectedly low strengths close to matrix value (~50 MPa) although with a modulus of 7 GPa. The UD specimens exhibited values of 130 MPa and 11.5 GPa for strength and modulus respectively. All the modulus values observed were close to that expected from the rule of mixtures. Samples immersed in deionised water at 37°C revealed rapid mechanical property loss, more so for the UD and 0–90o samples. It was suggested that continuous fibres wicked the degradation media into the composite plates which sped up the deterioration of the fibre-matrix interface. The effect was less pronounced in the non-woven random mat laminates due to the discontinuous arrangement of fibres within the composite, making it less prone to wicking. Random mat composites revealed a higher mass loss than the UD and 0°–90° specimens, it was suggested this was due to the higher fibre volume fractions of these composites and SEM studies revealed voidage around the fibres by day 3. Studies of pH of the degradation media showed similar profiles for all the composites investigated. An initial decrease in pH was attributed to the release of phosphate ions into solution followed by a gradual return back to neutral.     

Morphological,thermal, rheological,and mechanical properties of polypropylene-nanoclay composites prepared from masterbatch in a twin screw extruder

A commercial homopolymer polypropylene was melt blended with commercial nanoclay masterbatch at different concentrations of nanoclay using twin screw extruder (TSE). The influence of three different concentrations (5, 10, and 15 wt%) of the nanoclay on the morphological, thermal, rheological, and mechanical properties was investigated. The morphology of the nanocomposites was characterized using Scanning Electron Microscope (SEM), whereas, the thermal behavior (e.g., melting and crystallization) was characterized using Differential Scanning Calorimetry (DSC). The melt rheology and dynamic mechanical properties were analyzed using a torsional rheometer. Additionally, the tensile properties were characterized as well. The morphological analysis showed that the nanoclay was well distributed in the PP matrix as indicated by the SEM micrographs. The DSC results showed that the presence of nanoclay in the PP matrix increased the degree of crystallinity of PP-nanoclay composites, which reached a maximum at 5 wt% of nanoclay concentration. However, the melting temperature of the PP-nanoclay composites was not affected by the presence of nanoclay particles. In addition, rheological analysis showed that the melt response gradually changed from pseudo-liquid like to pseudo-solid like as the nanoclay concentration increased. Moreover, the storage modulus (G′) increased by increasing nanoclay content. Furthermore, tensile test results showed that the addition of nanoclay leads to a significant enhancement in the mechanical properties of the PP nanocomposites.     

Viscoelastic behavior of nano-hydroxyapatite reinforced poly(vinyl alcohol) gel biocomposites as an articular cartilage

Nanohydroxyapatite reinforced poly(vinyl alcohol) gel (nano-HA/PVA gel) composites has been proposed as an articular cartilage repair biomaterial. In this paper, nano-HA/PVA gel composites were prepared by in situ synthesis nano-HA particles in PVA solution and accompanied with freeze/thaw method. The influence of nano-HA content, PVA concentration, test frequency and freeze/thaw cycle times on the viscoelastic behavior of nano-HA/PVA gel composites were evaluated using dynamic mechanical thermal analysis (DMTA). The results showed that both storage modulus and loss modulus firstly increased and then presented decreasing trend with the rise of nano-HA content. Their maximum values were obtained while nano-HA content was 6%. Furthermore, the G′ and G″ of the composites improve with the increase of PVA concentrations and freeze/thaw cycle times. This effect was more distinct at low freeze/thaw cycles. The phase angle (tan δ) of the pure PVA gel is larger than that of the nano-HA/PVA composites at the test frequency spectra, but all the phase angle values of the tested composites were close to that of nature bone.     

Bonding interactions and stability assessment of biopolymer material prepared using type III collagen of avian intestine and anionic polysaccharides

The present study demonstrate bonding interactions between anionic polysaccharides, alginic acid (AA) and type III collagen extracted from avian intestine used for the preparation of thermally stable and biodegradable biopolymer material. Further the study describes, optimum conditions (pH, temperature and NaCl concentration) required for the formation of fibrils in type III collagen, assessment on degree of cross-linking, nature of bonding patterns, biocompatibility and biodegradability of the cross-linked biomaterial. Results revealed, the resultant biopolymer material exhibit high thermal stability with 5–6 fold increase in tensile strength compared to the plain AA and collagen materials. The degree of cross-linking was calculated as 75%. No cytotoxicity was observed for the cross-linked biopolymer material when tested with skin fibroblast cells and the material was biodegradable when treated with enzyme collagenase. With reference to bonding pattern analysis we found, AA cross-linked with type III collagen via (i) formation of covalent amide linkage between –COOH group of AA and ε-NH₂ group of type-III collagen as well as (ii) intermolecular multiple hydrogen bonding between alginic acid –OH group with various amino acid functional group of type-III collagen. Comparisons were made with other cross-linking agents also. For better understanding of bonding pattern, bioinformatics analysis was carried out and discussed in detail. The results of the study emphasize, AA acts as a suitable natural cross-linker for the preparation of wound dressing biopolymer material using collagen. The tensile strength and the thermal stability further added value to the resultant biopolymer.     

Inelastic behaviour of collagen networks in cell–matrix interactions and mechanosensation

The mechanical properties of extracellular matrix proteins strongly influence cell-induced tension in the matrix, which in turn influences cell function. Despite progress on the impact of elastic behaviour of matrix proteins on cell–matrix interactions, little is known about the influence of inelastic behaviour, especially at the large and slow deformations that characterize cell-induced matrix remodelling. We found that collagen matrices exhibit deformation rate-dependent behaviour, which leads to a transition from pronounced elastic behaviour at fast deformations to substantially inelastic behaviour at slow deformations (1 μm min⁻¹, similar to cell-mediated deformation). With slow deformations, the inelastic behaviour of floating gels was sensitive to collagen concentration, whereas attached gels exhibited similar inelastic behaviour independent of collagen concentration. The presence of an underlying rigid support had a similar effect on cell–matrix interactions: cell-induced deformation and remodelling were similar on 1 or 3 mg ml⁻¹ attached collagen gels while deformations were two- to fourfold smaller in floating gels of high compared with low collagen concentration. In cross-linked collagen matrices, which did not exhibit inelastic behaviour, cells did not respond to the presence of the underlying rigid foundation. These data indicate that at the slow rates of collagen compaction generated by fibroblasts, the inelastic responses of collagen gels, which are influenced by collagen concentration and the presence of an underlying rigid foundation, are important determinants of cell–matrix interactions and mechanosensation.     

Effect of matrix glass transition on reinforcement efficiency of epoxy-matrix composites with single walled carbon nanotubes,multi-walled carbon nanotubes,carbon nanofibers and graphite

This study compares the mechanical and thermal properties of glassy and rubbery epoxy–matrix composites reinforced with 1 and 4 wt.% single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphite, and carbon nanofibers (CNFs). The tensile modulus of most glassy composites was higher than that of the epoxy and increased with higher filler concentration and 4% graphite/epoxy and 4% SWCNT/epoxy exhibited approximately the same highest tensile modulus. The elongation of glassy composites was significantly lower than that of the epoxy and decreased with increasing filler loading. Most rubbery composites showed a higher tensile modulus and elongation than the epoxy and the modulus increased with rising filler content and 4% SWCNT/epoxy showed the highest tensile modulus and tensile strength. In the rubbery regime, glassy and rubbery composites displayed a higher storage modulus than the corresponding epoxy and 4 wt.% SWCNT/epoxy composites showed a 300% improvement in storage modulus compared to the epoxy.     

Comparison of various mixtures of β-chitin and chitosan as a scaffold for three-dimensional culture of rabbit chondrocytes

With the use of a recently created chitosan neutral hydrogel, we have been able to create various mixtures of chitin and chitosan without changing their characteristics even at room temperature. The aim of this study was the initial comparison of various mixtures of β-chitin and chitosan as a scaffold for rabbit chondrocyte culture. We created five types of sponges: pure β-chitin, pure chitosan, 3:1, 1:1, and 1:3 β-chitin-chitosan. The absorption efficiencies of chondrocytes in all five types of sponges were found to be around 98%. The mean concentrations of chondroitin sulfate were statistically different neither at week 2 nor at week 4 postculture between the types of sponges. The content of hydroxyproline in the β-chitin sponge was significantly greater than in other sponges at week 4 postculture. From the histochemical and immunohistochemical findings, the cartilage-like layer in the chondrocytes-sponge composites of all five types of sponges was similar to hyaline cartilage. However, only immunohistochemical staining of type II collagen in the pure β-chitin sponge was closer to normal rabbit cartilage than other types of sponges. The pure β-chitin sponge was superior to other sponges concerning the content of extracellular matrices of collagen.     

Impedance-spectroscopy analysis of oriented and mercerized bamboo fiber-reinforced epoxy composite

Bamboo fiber-reinforced epoxy composites were fabricated with untreated and alkali treated bamboo fibers. Dielectric, electric modulus, ac, and dc conductivity studies were carried out to rationalize the dielectric behavior of bamboo/epoxy composites. Composites of two fiber orientation parallel and perpendicular to the electric field were prepared. The dielectric behavior and electric modulus spectra of the composites were characterized using standard impedance analyzer. Dielectric properties were analyzed as a function of frequency (95 Hz–2 MHz) for temperatures in the range from 30 to 180 °C. Real part of dielectric constant (ε′), conductivity, and dielectric dissipation factor (tan δ) of 0° oriented bamboo/epoxy composites were higher than that of 90° oriented composites. Conductivity activation energy, tan δ, ε′, and volume resistivity decreased with increase in frequency at all the temperatures under study. Mercerization reduces the water absorption in bamboo fibers and thus improves corresponding dielectric properties of composites. Relaxation times 39.80 μs and 258.5 μs for 0° and 90° oriented bamboo/epoxy composites were calculated respectively from the relaxation peaks observed in electric modulus spectra at 180 °C.     

The effect of silane treated- and untreated-talc on the mechanical and physico-mechanical properties of poly(lactic acid)/newspaper fibers/talc hybrid composites

This paper evaluates the effect of the addition of silane treated- and untreated- talc as the fillers on the mechanical and physico-mechanical properties of poly(lactic acid) (PLA)/recycled newspaper cellulose fibers (RNCF)/talc hybrid composites. For this purpose, 10 wt% of a talc with and without silane treatment were incorporated into PLA/RNCF (60 wt%/30 wt%) composites that were processed by a micro-compounding and molding system. PLA is utilized is a bio-based polymer that made from dextrose, a derivative of corn. Talc is also a natural product. The RNCF and talc hybrid reinforcements of PLA polymer matrix were targeted to design and engineer bio-based composites of balanced properties with added advantages of cost benefits besides the eco-friendliness of all the components in the composites. In this work, the flexural and impact properties of PLA/RNCF composites improved significantly with the addition of 10 wt% talc. The flexural and impact strength of these hybrid composites were found to be significantly higher than that made from either PLA/RNCF. The hybrid composites showed improved properties such as flexural strength of 132 MPa and flexural modulus of 15.3 GPa, while the unhybridized PLA/RNCF based composites exhibited flexural strength and modulus values of 77 MPa and 6.7 GPa, respectively. The DMA storage modulus and the loss modulus of the PLA/RNCF hybrid composites were found to increase, whereas the mechanical loss factor (tan delta) was found to decrease. The storage modulus increased with the addition of talc, because the talc generated a stiffer interface in the polymer matrix. Differential scanning calorimetry (DSC) thermograms of neat PLA and of the hybrid composites showed nearly the similar glass transition temperatures and melting temperatures. Scanning electron microscopy (SEM) micrographs of the fracture surface of Notched Izod impact specimen of 10 wt% talc filled PLA/RNCF composite showed well filler particle dispersion in the matrix and no large aggregates are present. The comparison data of mechanical properties among samples filled with silane-treated- and untreated- talc fillers showed that the hybrid composites filled with silane treated talc displayed the better mechanical prosperities relative to the other hybrid composites. Talc-filled RNCF-reinforced polypropylene (PP) hybrid composites were also made in the same way that of PLA hybrid composites for a comparison. The PLA hybrid bio-based composites showed much improvement in mechanical properties as compared to PP-based hybrid counterparts. This suggests that these PLA hybrid bio-based composites have a potential to replace glass fibers in many applications that do not require very high load bearing capabilities and these recycled newspaper cellulose fibers could be a good candidate reinforcement fiber of high performance hybrid biocomposites.     

Mechanical and electrical properties of hot-pressed borosilicate glass matrix composites containing multi-wall carbon nanotubes

Borosilicate glass matrix composites reinforced with 10 wt% multiwall carbon nanotubes (CNTs) were fabricated using a conventional powder processing route and uniaxial hot pressing. The microstructure of the composites contained aggregates of CNTs which had not been infiltrated by the viscous glass during hot-pressing leaving a ∼9% residual porosity. As a result, the mechanical properties (hardness, elastic modulus, fracture toughness and fracture strength) were not improved in comparison to those of the monolithic glass matrix. However the brittleness index (B), which is the ratio of hardness to fracture toughness, decreased with addition of CNTs, which indicates that the composites should exhibit improved contact damage and wear resistance. Electrical resistivity measurements revealed that the addition of 10 wt% CNTs to the normally insulating borosilicate glass decreased its resistivity to 13 Ω cm in comparison to the high value (10¹⁵ Ω cm) of the monolithic glass.     

The attachment,spreading and growth of baby hamster kidney cells on collagen,chemically modified collagen and collagen-composite substrata

Various replicates of collagen substrata were prepared to study the attachment, growth and spreading of baby hamster kidney (BHK) cells. Cell attachment was measured in both the presence and absence of serum. Spreading and growth did not occur in the absence of serum. Attachment to fibrous collagen was less than that found with glass, rat-tail tendon collagen or films prepared from pepsin-solubilized collagen (PS-collagen). Incorporation of hyaluronate, heparin and protamine sulphate into the fibrous collagen and the acetylation of fibrous collagen had little effect. However, incorporation of chondroitin sulphate or chemical modification of fibrous collagen by either methylation or succinylation increased BHK cell attachment. In the absence of serum, the attachment to collagen, acetylated collagen and collagen composites was reduced. The reduction in attachment was marked with fibrous collagen and gelatin films, but less so with collagen composites, acetylated collagen, rat-tail tendon and PS-collagen films. Interestingly, attachment to succinylated collagen and methylated collagen was largely unaffected by the absence of serum, and possible reasons for this are discussed. Cell shape measurements showed decreased spreading of BHK cells on chemically modified collagen films, especially on gelatin films and dried PS-collagen gels. Cell shape and spreading on PS-collagen, rat-tail tendon collagen and collagen-composite films was found to be similar to that on fibrous collagen. BHK cell growth on fibrous collagen, chemically modified collagens, collagen composites, rat-tail tendon and PS-collagen films was similar to that found on plastic tissue culture substrate. Denaturation of fibrous collagen resulted in decreased growth, and BHK cell growth was markedly reduced on PS-collagen gels and dried gels.     

Effects of introducing silica particles on the rheological properties and crystallization behavior of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET)/silica composites were prepared by melt compounding, and their rheological properties and isothermal crystallization were discussed. Introduction of silica particles (0.5–2 wt.%) increased the storage modulus (G′) and decreased loss tangent (tanδ). However, the effect of the particles on rheological properties became negligible at a high frequency more than ca. 70 rad/s. In the Cole–Cole plot, the PET/silica composites showed little deviation from the master curve regardless of the presence of silica particles. The particles increased the relaxation time of PET at particularly low frequency. The isothermal crystallization kinetics of PET/silica was examined using a differential scanning calorimeter (DSC). The half-time of crystallization was decreased with increasing the silica content. The incorporation of silica particles decreased the equilibrium melting temperature by ca. 5.5 °C. In addition, the composites exhibited higher average value of Avrami exponent (2.7–2.9) in comparison with that of pure PET (2.2).     

Effects of pH and temperature on microstructure and morphology of hydroxyapatite/collagen composites synthesized in vitro

Hydroxyapatite/collagen composites (HAp/Col) were synthesized, in vitro, using the self-organization mechanism, by the co-precipitation of collagen, extracted from pork skin, and aqueous H₃PO₄ and Ca(OH)₂. The effects of pH and temperature, on the microstructure and morphology of HAp/Col composites, were extensively studied.It was shown that the yield of the composite is closely related to the pH value, during preparation. At high pH, the white precipitate of the composites was formed in a large quantity. In contrast, the yield was quite low, at low pH, owing to the dissolution of the composite precipitates. The electrophoretogram of the as-prepared composite shows that the α1(I) chain was dominant and that there was no protein residue in the supernatant of the reaction solution. Accordingly, it is reasonable to assume that the collagen molecules had completely reacted with hydroxyapatite.A closer look at the structural evolution of HAp/Col composites revealed that, at pH = 5, there was no sign of interfacial interaction between hydroxyapatite and collagen, during the first 36 h. In contrast, under alkaline conditions, the amount of α(I) chains was indeterminate, at the start of precipitation, while the concentration of β-chains decreased gradually. The chemical structure of HAp/Col, as determined by FTIR spectra, revealed that the bending vibration of phosphate contours can be attributed to the dissolution of HAp, at low pH. The crystalline of HAp was readily discerned, for all samples, as revealed by the XRD patterns. The morphology of the HAp/Col, prepared under neutral to alkaline conditions (7 ≤ pH ≤ 9), exhibited a compact, coral reef-like structure. In summary, HAp/Col composites can be synthesized, in vitro, under conditions native to animal physiology. The desirable conditions for synthesis are a higher pH (8 to 9) and a temperature of 40 °C.     

Tensile and flexural properties of injection-moulded short glass fibre and glass bead ABS composites in the presence of weldlines

The effect of weldline on tensile and flexural properties of ABS reinforced with short glass fibres (ABS/GF) and spherical glass beads (ABS/GB) was investigated as a function of glass fibre and glass bead concentrations. The weldline was formed in the moulded specimens by direct impingement of two opposing melt fronts (i.e. cold weld). It was found that elastic modulus of ABS/GF composites, with or without weldlines increased linearly with increasing volume fraction of fibres (ϕ_f), according to the rule-of-mixtures for moduli. The presence of weldline reduced tensile and flexural modulus of the ABS/GF composites. Weldline integrity factor for elastic modulus of ABS/GF composites decreased linearly with increasing ϕ_f. Results showed that tensile and flexural strength of ABS/GF increased with increasing ϕ_f in a nonlinear fashion. Flexural strength was consistently greater than tensile strength for the same ϕ_f. Weldline affected both strengths in a significant way; weldline integrity factor decreased with increasing ϕ_f and was independent of loading mode. Tensile and flexural modulus of ABS/GB composites increased linearly with increasing volume fraction of glass beads (ϕ_b), showing no loading mode dependency. Although modulus of the ABS/GB system was not affected significantly by the weldline, its strength was affected, and more so in flexure than in tension. Weld and unweld strengths decreased with increasing ϕ_b in both tension and flexure according to Piggott and Leidner relationship; for the same ϕ_b, flexural strength was always greater than tensile strength. Weldline integrity factor for tensile strength of ABS/GF system was considerably lower than that for ABS/GB system but weldline integrity factor for flexural strength was almost the same for the two composite systems.     

Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites

A novel biocomposite of carbon fiber (CF) reinforced hydroxyapatite (HA)/polylactide (PLA) was prepared by hot pressing a prepreg which consisting of PLA, HA and CF. The prepreg was manufactured by solvent impregnation process. Polymer resin PLA dissolved with chloroform was mixed with HA. After reinforcement CF bundle was impregnated in the mixture, the solvent was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 170°C for 20 min. A study was carried out to investigate change in mechanical properties of CF/HA/PLA composites before and after degradation in vitro. The composites have excellent mechanical properties. A peak showed in flexural strength, flexural modulus and shear strength aspects, reaching up 430 MPa, 22 GPa, 212 MPa, respectively, as the HA content increased. Degraded in vitro for 3 months, the flexural strength and flexural modulus of the CF/HA/PLA fell 13.2% and 5.4%, respectively, while the shear strength of the CF/HA/PLA composites remains at the 190 MPa level. The SEM photos showed that there were gaps between the PLA matrix and CF after degradation. Water uptake increased to 5%, but the mass loss rate was only 1.6%. The pH values of the PBS dropped less than 0.1. That’s because the alkaline of HA neutralize the acid degrades from PLA, which can prevent the body from the acidity harm.