Fibre matrix adhesion of natural fibres cotton,flax and hemp in polymeric matrices analyzed with the single fibre fragmentation test

In this research the adhesion and the resulting interfacial shear strength (IFFS) between the natural fibres flax, hemp and cotton and the polymer matrices polypropylene with coupling agent (MAPP) and polylactide acid (PLA) was surveyed with the single fibre fragmentation test (SFFT). The adhesion between MAPP and the fibres was good enough to produce fragments, whereas the adhesion between PLA and flax was too weak to transmit enough tension for fibre cracks which is clearly visible on SEM-photographs. Comparing the IFFS values of the fibres in MAPP with an equal fibre diameter shows that the IFFS value of flax is highest with 7.09 N/mm² followed by hemp 6.13 N/mm². The IFFS of cotton is a lot smaller (0.664 N/mm²). The critical fragmentation or fragmentation length of the bast fibres flax (3.16 mm) and hemp (3.20 mm) in MAPP is smaller than the critical fragmentation length of cotton (5.03 mm). The adhesion between the lignocellulosic fibres and MAPP is much better than between the lignin and pectin free cellulose fibre and MAPP. Possible reasons for this — the surface structure of the cotton fibre and its different chemical composition being made up of only cellulose, hemi-cellulose and wax with no pectin or lignin present — are discussed.     

Enhancing the Fibre Matrix Adhesion of Natural Fibre Reinforced Polypropylene by Electron Radiation Analyzed with the Single Fibre Fragmentation Test

The effects of electron radiation on natural fibre reinforced polypropylene have been analyzed with the single fibre fragmentation test. Specimens of single hemp, flax, ramie and cotton fibres/fibre bundles embedded in a polypropylene sheet were irradiated with electron radiation of 10 MeV with intensities of 5, 15 and 33 kGy. The radiation led to a strain reduction of the polypropylene but did also improve the adhesion between polymer and flax, hemp and cotton fibres/fibre bundles. The critical fragmentation length and the interfacial shear strength (IFSS) of the composite specimens have been determined showing a clear increase of the IFSS of up to 50% compared to specimens with applied coupling agents. Due to the high strain reduction of the PP at intensities of 15 and 33 kGy the different fibres could only be compared at 5 kGy. The ramie fibre specimens could be analyzed at 5 and 15 kGy intensity showing higher IFSS values at the higher intensity. A possible explanation for the improvement is the forming of radicals with the cellulose chains of the natural fibres and the polypropylene molecules leading to crosslinking and, therefore, better adhesion between the different components.     

Effect of the molecular weight of sizing agent on the surface of carbon fibres and interface of its composites

The influence of different molecular weight sizing agent on the performances of carbon fibres and carbon fibres composites were studied. Three different kinds of molecular weight sizing were used. Surface composition of the fibres modified with aqueous sizing and topographies of carbon fibres surface were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscope (SEM). The interlaminar shear strength and hygrothermal ageing test have been used to study the effect of fibres coatings on the adhesion of surface. The results of the study indicate that the molecular weight of sizing agent has an important influence to the carbon fibres and carbon fibres composites. The high and low molecular weight sizing agent decreased the interfacial shear strengths and hygrothermal ageing of carbon fibres composite. The moderate molecular weight of sizing agent showed an improvement of the interfacial adhesion and hygrothermal ageing.     

Mechanical Properties and Morphology of Polylactide Composites with Acrylic Impact Modifier

Polylactide (PLA) composites with acrylic impact modifier BPM, i.e., PLA/BPM composites, were produced by the melt blending method. The effects of BPM on the thermal properties, melting behaviors, and dynamic mechanical properties of the PLA/BPMs were investigated by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Tensile strength, flexural strength, and modulus of the injection molded specimens were measured by an Instron tensile machine. The influence of BPM on the impact strength of injection molded PLA/BPM composites was examined using an impact tester. The morphology of cryofractured surfaces and fracture surfaces of the composites after the tensile and impact testing was also investigated using scanning electron microscope. The test results show that the composites with BPM possess better flexibility when compared with neat PLA. However, the notched Izod impact strength showed improvement only when the BPM content was higher than 15 wt%.     

Effect of emulsifier content of sizing agent on the surface of carbon fibres and interface of its composites

In this work, carbon fibres were sized with different emulsifier content sizing agent in order to improve the performances of carbon fibres and the interface of carbon fibres composites. The surface characteristic changing after modification was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM). Wetting and surface energy along with contact angles were determined by the dynamic contact angle analysis test (DCAT). At the same time, the single fibre strengths and weibull distributions were also studied in order to understand the effect of the emulsifier content of sizing agent on the carbon fibres. The interfacial shear strength and hygrothermal ageing of the composites were measured which showed a different enhancement, respectively. The results revealed that sizing agent E-3 showed better interface adhesion between fibres and matrix and sizing agent E-2 sized carbon fibre has better ageing resistant properties.     

Microcellular and Solid Polylactide–Flax Fiber Composites

Polylactide–flax fiber composites with 1, 10 and 20 wt% fiber were melt-compounded and subsequently molded via the conventional and microcellular injection-molding processes. Silane was used as a coupling agent. The effects of fiber and silane content on cell morphology, static and dynamic mechanical properties, and crystallization properties have been studied. The average cell size decreased while the cell density increased with the fiber content. The degree of crystallinity increased with the fiber content. Silane treatment of fibers affected neither the cell morphology nor the degree of crystallinity. The toughness and strain-at-break of solid samples decreased with the fiber content while silane treatment increased both properties; however, neither fiber content nor silane treatment had much influence on the toughness and strain-at-break of microcellular samples. The specific modulus of both solid and microcellular samples increased with the fiber content. The specific strength of the solid and microcellular PLA–flax composites were only slightly lower than that of their solid and microcellular pure PLA counterparts. Overall, the toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than that of their solid counterparts. The storage modulus of the PLA–flax composites with 10 and 20% fiber contents was higher than that of pure PLA.     

Mechanical,Biodegradation and Morphological Properties of Sisal Fiber Reinforced Poly(Lactic Acid) Biocomposites

Sisal fiber-reinforced poly(lactic acid) (SF/PLA) biocomposites were prepared by melt mixing and subsequent compression molding. The effect of fiber content and sodium hydroxide (NaOH) concentration, used for the fiber mercerization, on the properties of the biocomposites was investigated. It was found that the SFs had a large potential for improving the mechanical properties of the biocomposites. The tensile strength and impact strength increased linearly up to a fiber content of 20%, and then decreased due to the fiber agglomeration. The water absorption was enhanced with increasing the SF content owing to the SFs containing an abundance of hydroxyl groups. The biodegradability of the SF/PLA biocomposites increased similarly. Furthermore, the mercerization led to an increase of the mechanical properties of the biocomposites, which normally depended on the fiber-matrix adhesion. The mercerization had competing effects on the water absorption and biodegradability, including not only the positive function of the improved hydrophilicity of the mercerized-SF but also the negative role of the increase of fiber-matrix interfacial adhesion. Overall, the optimum SF load for mechanical properties was 20?wt% due to a good balance between the reinforcement and distribution of the SFs, whereas the 6% NaOH concentration was optimal owing to the resulting fibers yielding the highest mechanical properties and acceptable water resistance and biodegradability.     

Foaming and Damping Properties of Ethylene Vinyl-Acetate Copolymer/Polylactic Acid Blends

With ethylene vinyl-acetate copolymer (EVM) and polylactic acid (PLA) blends as the matrix, dicumyl peroxide (DCP) as the curing agent and azodicarbonamide (AC) as the foaming agent, EVM/PLA foamed blends were prepared by compression molding. The effects of different amounts of AC, DCP, and silica, as well as varying foaming time, on the cell structure and damping properties of the EVM/PLA-foamed blends were examined by scanning election microscopy (SEM) and dynamic mechanical analysis (DMA). The results showed that the cell size and damping properties varied little with increasing AC content in the compounds; however, the cell size declined slightly as DCP increased and the damping properties rose slightly, exhibiting an optimum set of properties at 5 phr of DCP. The cell size declined dramatically and damping increased significantly as the foaming time was increased. Moreover, both suddenly increased after 5 min foaming. It was found that the damping properties of the foamed materials increased with decreasing cell size and increasing number of cells. The cell size also decreased and damping properties increased as the silica content was increased. The silica interacted more strongly with EVM than with PLA.     

Adhesion of epoxy-thermoplastic and polysulfone-LCP matrices to fibres

This work investigated the adhesion strength τ of the joints of polymer blends with fibres. Blends of polysulfone with LC-polyether and epoxy resin (based on DGEBA) with polysulfone, polyetherimide and poly(arylene ether ketone) were taken as matrices. Steel wire, polyamide (nylon-6) and glass fibres were used as substrates. The adhesion strength was determined by the 'pull-out' technique. It was found that incorporation of LCP into polysulfone and incorporation of thermoplastics into epoxy matrix resulted in non-additive relationships between the adhesion strength and modifier (LCP or thermoplastic) content C. In the case of epoxy-polysulfone, epoxy-polyetherimide and polysulfone-LCP matrices, such τ-C dependencies were described by curves showing a maximum. Optimal (maximal) adhesion strength of the blend/fibre joints was obtained at 10 wt% of polysulfone, 15 wt% of polyetherimide and poly(arylene ether ketone) in epoxy resin and 2–5 wt% of LC-polyether in polysulfone. Possible mechanisms of the interface strength enhancement are discussed.     

Nanocellulose enhanced interfaces in truly green unidirectional fibre reinforced composites

One of the main problems in fabricating natural fibre reinforced polymers is the poor adhesion between intrinsically polar plant fibres and non-polar polymer matrices. We have developed a truly green technique of modifying natural fibre (hemp and sisal) surfaces to improve the interaction between the fibres and polymers by attaching nano-scale bacterial cellulose to the fibre surfaces. These modified natural fibres were then incorporated into the renewable polymers cellulose acetate butyrate (CAB) and poly-L-lactic acid (PLLA). Unidirectional natural fibre reinforced composites were manufactured to investigate the impact of the surface modification on the fibre and interface dominated composite properties. Both the tensile strength parallel as well as perpendicular to the fibres of the composites reinforced by bacterial cellulose modified natural fibres were found to increase significantly, especially in the case of a PLLA matrix. In case of modified sisal reinforced PLLA the parallel strength increases by 44% and the off-axis composite strength by 68%. Scanning electron microscopy observations of the composite fracture surfaces confirm the improved interaction between the fibre and the polymer matrix.     

Correlation of the Morphological and Mechanical Properties of a Biodegradable Blend Based on Polylactic Acid

A series of binary and ternary blends composed of polylactic acid (PLA), low-density polyethylene (LDPE), and chitosan (CS) were prepared and characterized in terms of their morphological and mechanical properties. The mechanical properties of the prepared blends, including tensile properties and impact strength, were compared with neat PLA. In addition, the effect of incorporation of maleic anhydride-grafted linear low-density polyethylene (LLDPE-g-MA) as a compatibilizing agent, and the order of mixing on the mechanical and morphological properties of the ternary blends were also studied. It was observed that addition of CS enhanced the stiffness of PLA/LDPE blends while it decreased the toughness and tensile strength. It was demonstrated that addition of LLDPE-g-MA, up to 10 wt%, had no significant compatibilizing effect. However, the mechanical results indicated that when 15 wt% of LLDPE-g-MA was loaded, it started to play a compatibilizing role and caused an improvement in the toughness properties of ternary blend.     

Melting and Crystallization Behaviors of Poly(Lactic Acid) Modified with Graphene Acting as a Nucleating Agent

Graphene (GN)-filled polylactic acid (PLA) nanocomposites were prepared through a solution blending method with GN weight percent ranging from 0.5 to 2?wt%. Rheological, melting and crystallization behaviors of the prepared PLA/GN nanocomposites were investigated by means of dynamic rheological measurements and differential scanning calorimetry (DSC). The shear viscosities of the PLA/GN nanocomposites decreased with increasing GN content, which was remarkably different from previous reports on the modifications using traditional nanofillers (e.g., clay, carbon nanotubes, etc.). The nonisothermal melt crystallization kinetic analysis suggested that GN served as a nucleating agent and could considerably promote the PLA’s crystallization through heterogeneous nucleation. Our findings suggested that at relatively low cooling rates (??≤?10?°C/min) even a small amount of GN promoted the nucleation and considerably increased the crystallization rate. However, the crystallinity began to decrease at higher cooling rates (e.g., ??≥?20?°C/min), especially when the GN content was high (e.g., 2?wt%), possibly owing to the GN aggregation effect considering PLA is a slowly crystallizing polymer.     

Multi-interfaces investigation on the PLA composites toughened by modified MWCNTs

The effects of multiwalled carbon nanotubes (MWCNTs) modified by silane coupling agent (Trademark in china was KH570) and lactide (LA) on the properties of poly(lactic acid) (PLA) composites were investigated in this paper. The Scanning electronic microscopy (SEM) images showed that MWCNTs modified by both KH570 and LA, which constructed the MWCNTs-KH570-PLA nanocapsules, owned the best performances to toughen PLA. These nanocapsules were developed by solid multilayered interfaces and efficiently enhanced tnced the interfacial adhesion between PLA and MWCNTs. Polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis further verified that modified MWCNTs refined the PLA grain size and improved its crystallization. Moreover, observed by thermogravimetry (TG), the thermal stability of PLA was also improved. Then it could be drawn the conclusion that among these modified MWCNTs, MWCNTs-KH570-PLA nanocapsule was the best in toughening PLA, and the tensile strength of MWCNTs-KH570-PLA/PLA composite rose by 39.97% and its impact strength by 51.61%.     

Influence of Fiber Surface Treatment on Mechanical Properties of CF/PET Composites

Carbon fiber (CF) / poly (ethylene terephthalate) (PET) composites were prepared with various contents (2–15wt%) of short carbon fibers. To investigate the effect of surface treatment of the CF on the mechanical properties of the composites, three specimens were prepared; those with short carbon fibers (called SCF), short carbon fibers oxidized with nitric acid (called NASCF) and the fibers oxidized with nitric acid and treated with silane coupling agent (called SCSCF). Flexural, tensile and impact tests were performed to observe mechanical behavior of the specimens. The morphology of the specimens was also studied with a scanning electron microscope (SEM). SCSCF composite had better mechanical properties than the other composites with the same content of carbon fibers since the coupling agent resulted in better interfacial adhesion between the fiber and the matrix.     

Toughening poly(lactic acid) (PLA) through in situ reactive blending with liquid polybutadiene rubber (LPB)

Abstract

Liquid polybutadiene rubber (LPB) was blended with poly(lactic acid) (PLA) through reactive and non-reactive routes to enhance the toughness of the PLA. The reactively blended PLA (PBR10) was prepared by melt blending the PLA with the LPB in the presence of dicumyl peroxide (DCP), a radical initiator, while the PB10 was just melt blended without the DCP. Fourier transform infrared (FTIR) spectra and wide-angle X-ray diffraction (WAXD) patterns were used to study the molecular structure of the blends. Properties were investigated through universal testing machine (UTM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM) analysis, and rheological measurements. The results indicated that the radical crosslinking by the DCP could increase the compatibility between the PLA and LPB and disperse the rubber particles at the nanoscale in the PLA matrix. As a result, the toughness and melt viscosity of the PLA was significantly enhanced through the reactive blending, which is promising for the practical application of the modified PLA in the area of packaging.     

Fibre-matrix interphases and interfaces in ceramic matrix composites processed by CVI

The fibre-matrix (FM) interfacial zone plays a key role in the mechanical behaviour of Si-C(O)/SiC inverse composites fabricated by chemical vapour infiltration (CVI) from ex-polycarbosilane Si-C(O) fibres precoated with pyrocarbon or boron nitride. It consists not only of the C (or BN) main interphase, but also of very thin secondary interphases (i.e. carbon and silica) resulting from the decomposition of the metastable Si-C(O) fibres thought to occur during the fabrication of the fibres and/or the composites. The FM interfacial zone may play two complementary roles: (i) it provides low-energy microcrack propagation paths parallel to the fibre axis, and (ii) it may act as a compliant buffer for the relaxation of the residual thermal compression stresses on the interface. The FM bond strength is low or moderate when a quasi-continuous thin layer of anisotropic carbon is present between the fibre and the main interphase and when the fibre surface remains smooth. The mechanical behaviour in tension is non-brittle with a wide non-linear stress-strain domain when the FM bonding is low or moderate, and tends to become brittle when the bonding is too strong. Finally, the thickness (and presumably the microtexture) of the carbon main interphase plays an important role in the oxidation resistance of the material, a self-healing behaviour being observed at high temperatures with a thin interphase. Replacing carbon by BN and adding an external coating of SiC (or Si₃N₄) to the composite improves its oxidation resistance.     

Reactive Compatibilization of Poly(Butylene Terephthalate)/Acrylonitrile-Styrene-Acrylate Blends by Epoxy Resin: Morphology and Mechanical Properties

The effect on the notched Izod impact strength of poly(butylene terephthalate) (PBT) by blending it with acrylonitrile-styrene-acrylate (ASA) was examined. Epoxy resin (ER) was demonstrated to be an efficient compatibilizer for the partially compatible blends of PBT/ASA. It requires only a very small amount of ER to improve the toughness of the PBT/ASA blends drastically. Furthermore, there exists an optimum proportion of ER added to achieve maximum notched Izod impact strength. Transmission electron microscopy (TEM) observation suggests that the ER in the PBT/ASA/ER blends suppressing the tendency of coalescence of ASA, leading to better dispersion of the ASA particles. Field emission scanning electron microscopy (FESEM) shows that ER enhances the phase dispersion and the interfacial adhesion between the PBT and ASA phases, it improves the compatibility between PBT and ASA. The compositions in the interphase was continuous, which results in multiphase composites with a graded interphase. It is suggested that enhanced interphase adhesion was necessary to obtain improved dispersion, fine phase morphology, and better toughness.     

Mechanical Properties and Morphology of Polypropylene/Polypropylene-g-Maleic Anhydride/Long Glass Fiber Composites

Long glass fiber (LGF)-reinforced polypropylene (PP) was prepared using a self-designed impregnation device. The effect of dicumyl peroxide (DCP) and maleic anhydride (MA) content on the compatibilizer, PP grafted with maleic anhydride (PP-g-MA), was investigated by means of scanning electron microscopy (SEM) and mechanical properties. The experimental results demonstrated that the increase of DCP and MA could effectively improve the interfacial interaction between PP and GF. Good interfacial adhesion between PP and GF in PP/ PP-g-MA /LGF composites was observed from SEM studies for the higher contents of MA. The best mechanical properties of PP/ PP-g-MA /LGF(30%) composites were obtained when the content of DCP and MA were 0.4 and 0.8 wt%, respectively. The storage modulus of the PP/PP-g-MA/LGF composites increased and then decreased with the content of MA. When the content of MA was 0.8 wt%, tan δ had the lowest value, indicating that the corresponding composites had the best compatibility.     

Observation of transcrystalline growth of PLA crystals on sisal fibre bundles and the effect of crystal structure on interfacial shear strength

Hot-stage microscopy was used to characterise crystal growth at the interface between sisal fibre bundles and a polylactic acid (PLA) matrix in order to better understand the mechanical properties of sisal fibre–PLA composites. Cooling rates and crystallisation temperatures and times were varied to influence crystalline morphology at the interface. Single sisal fibre bundles were evaluated in their as received state or treated with 6 wt.% caustic soda solution for 48?h at room temperature. A microbond shear test was used to characterise the shear strength of the interface as a function of fibre surface treatment. These tests were performed on sisal fibre bundles carefully embedded in flat films of PLA supported on card mounts. Fibre bundles in a PLA matrix were cooled from 180?°C at rates from 2 to 9?°C/min and then crystallised isothermally. For as received fibre bundles uneven growth of PLA spherulites occurred at all cooling rates and crystallisation temperatures. For caustic soda treated fibres, uneven spherulitic growth was observed at crystallisation temperatures at and above 125?°C. In contrast, transcrystalline growth was observed for samples cooled to 120?°C at cooling rates from 2 to 6?°C/min and then allowed to crystallise. The microbond shear strengths of untreated and caustic soda treated fibre bundles were evaluated using Weibull statistics and the caustic soda treated fibres exhibited higher interfacial shear strengths in comparison to untreated fibres, reflecting the development of a transcrystalline layer at the fibre to matrix interface.     

Surface adhesion and demolding force dependence on resist composition in ultraviolet nanoimprint lithography

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist system containing a base (either tripropyleneglycol diacrylate with shorter oligomer length or polypropyleneglycol diacrylate with longer oligomer length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine with homemade fixtures after imprinting the UV resist on a silicon stamp. While decreasing the cross-linking agent content from 49 to 0 wt% has little effect on the resist surface energy, it reduces the resist's elastic modulus drastically. The decrease in elastic modulus results in a decreased adhesion force at the resist/stamp interface thereby facilitating the demolding. The decrease in elastic modulus and, therefore, demolding force by lowering the cross-linking agent content was markedly less pronounced in tripropyleneglycol diacrylate-based resists due to its shorter oligomer length. These general findings will be useful in designing new resists for UV-NIL process.