Effect of carbon fibre surface on interfacial adhesive strengths in CFRP

Surface properties of polyacrylonitrile (PAN) based carbon fibres and their adhesive strengths with epoxy resin are investigated. The surfaces of PAN-based carbon fibres were characterized by krypton adsorption and oxygen chemisorption, amount of acidic surface functional groups, X-ray photoelectron spectroscopy and Raman spectroscopy. Interfacial shear, interlaminar shear and transverse tensile strengths were measured as the interfacial adhesive strengths. The epoxy resin used for the embedded single filament specimens was the same as that used in the matrix of the composites. Empirical equations between surface properties and adhesive strengths were calculated. All adhesive strengths in this study showed the best correlation with the active surface area ratio, defined as the surface area ratio of oxygen chemisorption to krypton adsorption. From these relationships, the effect of each surface property on adhesive strength is discussed.     

Enhancement of ceramic-to-metal adhesive bonding by excimer laser surface treatment

A silicon nitride (Si₃N₄) based ceramic cutting material and a structural alloy steel (SAE 4340) were surface-treated using a 800 mJ KrF excimer laser with an aim to improve the ceramic-to-metal bond strength. For these two materials, the effects of laser energy density and the number of pulses upon the surface morphologies of the laser-treated surfaces to be joined were examined. Conical surface microstructures were generally observed on the laser-treated surfaces of the Si₃N₄ material, and the number of conical features was found to be significantly influenced by the laser energy density. Moreover, the results of XPS have shown that the surface chemistry of the ceramic was altered after being laser treated. On the other hand, excimer laser treatment had caused the alloy steel surfaces be melted and resulted in some “beach-mark” features. However, the laser energy density has little effect on the overall surface morphology and the roughness of the treated surfaces. Shear tests were performed on adhesive bonded samples of the laser-treated ceramic and alloy steel. Significant improvement in adhesion shear strength was obtained for the laser-treated samples as compared with those tested in the as-received and mechanically abraded conditions. The required laser operation condition for achieving good shear joint strength was discussed.     

Formation of oxygen complexes in controlled atmosphere at surface of doped glassy carbon

The effects of boron and phosphorus incorporation in phenolic resin precursor to the oxidation resistance of glassy carbon have been studied. In order to reveal the nature and composition of the oxygen complexes formed at the surface of doped glassy carbon, under controlled atmosphere, the surface of the samples was cleaned under vacuum up to 1273 K. Specific functional groups, subsequently formed under dry CO₂ or O₂ atmosphere on the surface of boron-doped and phosphorus-doped glassy carbon samples, were examined using the temperature-programmed desorption method combined with mass spectrometric analysis. Characterization of surface properties of undoped and doped samples has shown that in the presence of either boron or phosphorus heteroatoms, a lower amount of oxygen complexes formed after CO₂ exposure, while, typically, higher amount of oxygen complexes formed after O₂ exposure. It has been concluded that the surface of undoped glassy carbon has a greater affinity towards CO₂, while in the presence of either boron or phosphorus heteroatoms, the glassy carbon surface affinity becomes greater towards O₂, under experimental conditions.     

Study of carbon fibre surface treatments by dynamic mechanical analysis

Dynamic mechanical and thermal analysis (DMTA) has been used to study the effects of surface treatment of carbon fibres on the viscoelastic properties of composites containing them. The fibres were treated by dip-coating, electro-polymerization, and plasma polymerization, and the behaviour of these fibres is compared with that of fibres treated by ordinary commercial oxidation and sizing procedures. Analysis of the experimental results is made both in terms of conventional approaches to viscoelastic behaviour and of the power-law analysis of the glass transition in an attempt to obtain suitable parameters for the evaluation of the effects of surface treatment.     

响应面优化法研究蔗糖苯酚树脂胶粘剂的合成

以蔗糖代替甲醛,在碱性条件下合成了一种环保型蔗糖苯酚树脂胶粘剂.用响应面优化法对蔗糖苯酚树脂的合成条件进行了优化,以树脂黏度作为考察指标,根据中心复合的设计原理对实验进行设计并对结果进行分析.研究了温度、时间、糖酚比和催化剂用量对反应的影响,得到最佳工艺条件为:反应温度95.63℃,反应时间5.26h,糖酚比2.6,催...     

Fracture toughness determination of adhesive and co-cured joints in natural fibre composites

Adhesive bonding has become more efficient in the last few decades due to the adhesives developments, granting higher strength and ductility. On the other hand, natural fibre composites have recently gained interest due to the low cost and density. It is therefore essential to predict the fracture behavior of joints between these materials, to assess the feasibility of joining or repairing with adhesives. In this work, the tensile fracture toughness ($G_{\text{n}}^{\text{c}}$) of adhesive joints between natural fibre composites is studied, by bonding with a ductile adhesive and co-curing. Conventional methods to obtain $G_{\text{n}}^{\text{c}}$ are used for the co-cured specimens, while for the adhesive within the bonded joint, the J-integral is considered. For the J-integral calculation, an optical measurement method is developed for the evaluation of the crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab sub-routine for the automated extraction of these quantities. As output of this work, an optical method that allows an easier and quicker extraction of the parameters to obtain $G_{\text{n}}^{\text{c}}$ than the available methods is proposed (by the J-integral technique), and the fracture behaviour in tension of bonded and co-cured joints in jute-reinforced natural fibre composites is also provided for the subsequent strength prediction. Additionally, for the adhesively-bonded joints, the tensile cohesive law of the adhesive is derived by the direct method.     

Effects of fibre surface silanisation on silica fibre/phenolics composites produced by resin transfer moulding process

Abstract

The effects of fibre surface silanisation on silica fibre/phenolics composites produced by the resin transfer moulding (RTM) solution impregnation route were investigated. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and micro-Wilhelmy method were used to evaluate the surface properties of silanised silica fibre. The interlaminar shear strength (ILSS) measurements and morphological observations of the silica fibre/phenolics composites were also performed. The interactions occurring between silica fibre and the components of phenolic resin solution affect the dynamic adsorption behaviour of phenolic resin onto fibre reinforcement. The competitive adsorption of ethanol as solvent onto silica fibre suppresses that of phenolic resin. Fibre surface silanisation by γ-aminopropyl-triethoxysilane (γ-APS), γ-glycidoxypropyl-trimethoxysilane (γ-GPS) and γ-methacryloxypropyl-trimethoxysilane (γ-MPS) leads to the improvement of mechanical interfacial properties of silica fibre/phenolics composites on one hand and decreases the inhomogeneities of resin distribution and mechanical interfacial properties at different regions of the RTM product on the other hand.     

Formation, structure and wettability of fluorescent nanolayers of oligoperoxide europium complexes adsorbed to glass surface

Formation kinetics and the nanolayer structure are determined for fluorescent complexes, which are composed of oligoperoxide and europium (OP-Eu), and are adsorbed to glass from water-ammonia solutions. The effective surface fraction x modified by OP-Eu is evaluated (with the Cassie equation) from receding contact angles. Its temporal behavior is repeated by the average adlayer thickness d, determined from ellipsometry, indicating rapid adsorption followed by gradual desorption. The fraction x increases with d to saturate at ∼ 90% for 57 nm. Atomic Force Microscopy micrographs and refractive indices do not reflect simple composite surfaces. Therefore a thickness effect on OP-Eu surface energy is also advocated. Fluorescent microscopy confirms luminescent properties of OP-Eu, applicable for protein detection.     

Selective reinforcement of an aluminium alloy by adhesive bonding with uniaxially aligned carbon fibre/epoxy composites

Aluminium alloy beams selectively reinforced on one or both surfaces with uniaxially aligned continuous carbon fibre-reinforced plastic were tested in flexure. Three manufacturing routes were employed; two of which involved the use of a room temperature curing adhesive and in the third pre-impregnated tapes were hot-pressed directly onto the alloy. Determined stiffness and strengths of the beams were in good agreement with the predictions of strength of materials theory. A 46% increase in stiffness, from 69 to 101 GNm⁻², and a 141% increase in yield strength, from 485 to 1170 MNm⁻², were obtained, for example, by incorporating 40% of cfrp by volume to make a sandwich beam. Although smaller increases in strength and stiffness result from less reinforcement, only 10% is sufficient to increase fatigue life by a factor of four.     

Role of fibre surface—matrix combination in carbon fibre reinforced epoxy composites

The effect of surface treatment of carbon fibres with concentrated as well as dilute nitric acid on the mechanical properties of carbon fibres has been reported. The role of the fibre—matrix interface in carbon fibre reinforced epoxy resin composites has been studied. Composites have been made both with untreated and surface treated carbon fibres and epoxy resin Araldite LY556 with different hardeners. Mechanical properties as well as fracture behaviour of these composites suggest that it is the physical interlocking between the fibres and the matrix, along with some chemical bonding between the two, and not the pure chemical bonding which yield better composites.     

Differentiation of domains in composite surface structures by charge-contrast X-ray photoelectron spectroscopy

An external bias is applied to two samples containing composite surface structures, while recording an XPS spectrum. Altering the polarity of the bias affects the extent of differential charging in domains that are chemically or electronically different to create a charge contrast. By utilizing this charge contrast, we show that two distinct silicon nitride and silicon oxynitride domains are present in one of the composite samples. Similarly, we use this technique to show that titanium oxide and silicon oxide domains exist as separate chemical entities in another composite sample.     

Improving the mechanical properties of glass-fibre-reinforced polyester composites by modification of fibre surface

Polyalkenyl-poly-maleic-anhydride-ester/amide type new experimental additives have been developed and used to achieve the better properties of glass-fibre-reinforced polyester composites. Two different commercial reinforcements have been investigated: a chopped glass fibre and a glass woven [0/90°] fabric materials. Based on their chemical structures, both were E-type. The surfaces of reinforcements have been treated with the dissolved form of polyalkenyl-poly-maleic-anhydride-ester, polyalkenyl-poly-maleic-anhydride-amide and polyalkenyl-poly-maleic-anhydride-ester-amide type experimental coupling additives then they have been used in fibre-reinforced thermoset. The coupling additives have had differences not only in their chemical structure and physical properties, but also in the fibre–matrix interaction that can also be affected by them. That is the reason why additives have resulted in numerous differences in the mechanical properties of the reinforced specimens. The most favourable effects have been found in the case when the glass-fibre surface was modified by polyalkenyl-poly-maleic-anhydride-ester-amide type additives. Moreover, results have referred to more favourable effects in case of chopped glass-fibre mat than in glass woven fabric composites. Tensile properties could be improved by 38.9% with that additive and flexure properties with 21.9% in those laminates. Tensile and flexure properties of glass woven [0/90°] fabric reinforced composites could be improved by 18.0%, and 40.1% comparing to the untreated glass fibres containing polyester composites with the same reinforcement. The polyalkenyl-poly-maleic-anhydride-ester type surface modifying additive has deteriorated the tensile and flexural properties of the laminates, but the dynamic properties have been more favourable than those of specimens with untreated glass fibres. Fibre–matrix interaction responsible for increased or decreased mechanical properties has been studied on SEM micrographs of the fractured face of composites. It has been found that the unfavourable results had been caused by the fibre slipping out the polyester matrix. Nevertheless, it has been supported by visual observation that the polyalkenyl-poly-maleic-anhydride-ester-amide additive managed to improve the adhesion between the fibres and the matrix.     

Characterising the surface adhesive behavior of tablet tooling components by atomic force microscopy

Purpose: The aim of this study is to develop an atomic force microscopy (AFM) based approach to study the adhesive forces between tabletting punches and model formulation ingredients, that can ultimately be used to understand and predict issues such as sticking during tabletting compression.

Methods: Adhesive interactions were studied between single lactose particles and coated tablet punches. The adhesion was measured at varying relative humidities (RHs) and the influence of surface roughness was investigated. Roughness parameters were measured with AFM imaging and a modeling approach used to predict the influence of roughness on adhesion.

Results: Surface roughness was found to play a significant role in the observed lactose-punch adhesion and the variation of this adhesion across the punch surface. Such differences between punches can be correlated to observations from industrial use. Adhesion forces were spatially mapped to indentify “hot spots” of high adhesion. A modeling approach can predict the relative adhesion of different surfaces from roughness data. The adhesion was also significantly affected by RH, for one type of punch causing a greater than 3× increase in adhesion between 30 and 60% RH. Interestingly, different punches showed different RH-adhesion behavior, relating to their hydrophilicity.

Conclusions: The work introduces a new method for screening tablet punch materials and tabletting conditions. Important factors to be considered when evaluating adhesive interactions in tablet compression have been highlighted. Correlations are observed between AFM adhesion results and tabletting behavior during manufacture. This provides a promising basis for a predictive approach toward combating tabletting issues.     

Formation and electrochemical investigation of ordered cobalt coordinated peptide monolayers on gold substrates

The monolayers composed of cobalt coordinated peptides were prepared on gold substrates by two different approaches. One was the self-assembly method, which was used to prepare a peptide monolayer on the gold substrate via the spontaneous attachment of peptides owing to the interaction between gold and sulfur at the N-terminal of the peptide. The other one was the stepwise polymerization method that was utilized to fabricate the unidirectionally arranged peptide monolayer by the stepwise condensation of amino acids from the initiator fixed on the gold substrate. Leu₂Ala(4-Pyri)Leu₆Ala(4-Pyri)Leu₆ sequence was chosen as the cobalt coordinated peptide. The 4-pyridyl alanines, Ala(4-Pyri)s, were introduced as ligands for cobalt to the leucine-rich sequential peptide. The complexation between cobalt and pyridyl groups of the peptide induced the formation of a stable α-helical bundle, which oriented perpendicularly to the substrate surface. In the case of the monolayer fabricated by the stepwise polymerization method, the direction of the peptide macro-dipole moment aligned unidirectionally, and the cobalt complexes were fixed in the monolayer to form the ordered arrangement. On the other hand, the peptides prepared by the self-assembly method formed the mixture of parallel and antiparallel packing owing to the dipole-dipole interaction. The spatial location of the cobalt complexes in the monolayer prepared by the self-assembly method was distorted, compared with that in the monolayer fabricated by the stepwise polymerization method. The vectorial electron flow through the peptide monolayer was achieved by the regular alignment of the peptide macro-dipole moment and the cobalt complexes in the monolayer fabricated by the stepwise polymerization method.     

Pillar-assisted epitaxial assembly of toric focal conic domains of smectic-a liquid crystals

SU-8 pillar-assisted epitaxial assembly of toric focal conic domains (TFCDs) arrays of smectic-A liquid crystals is studied. The 3D nature of the pillar array is crucial to confine and direct the formation of TFCDs on the top of each pillar and between neighboring pillars, leading to highly ordered square and hexagonal array TFCDs. Excellent agreement between the experimentally obtained critical pillar diameter and elasticity calculation is found.