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International audience; In recent years, natural fibers reinforced composites have received much attention because of their lightweight, recyclable, nontoxic, low cost and biodegradable properties. However, compatibility between hydrophilic natural fiber and hydrophobic polymer is low. One way to increase the fiber/matrix compatibility is to treat the fiber surface, using hydroxyl groups present on the upper layer of the high tenacity viscose. However, hydroxyl groups are not always accessible on the fibers surface due to impurities. It is thus mandatory to study the various possibilities to determine a good cleaning treatment, which furthermore does not have a negative influence on the mechanical properties of the fibers. In this article, (3-aminopropyl)triethoxysilane (APTES) is used to functionalize the fiber surface after cleaning them, in order to prepare the fibers for reactive injection of polyamide-6. In order to determine the influence of each cleaning/treatment on the physical and chemical properties of the fibers and to determine optimal treatments to increase fibers/matrix compatibility, various characterization methods (XPS, FTIR-ATR, SEM, EDX) were combined to theoretical results obtained by a design of experience.

This work aims to study the effect of reactive molding on polyamide-6 (PA6) based micro composites with either glass or high tenacity viscose as fibre reinforcements. For this purpose, microdroplet pullout test was found to be well suited to determine the interfacial shear strength. For pull-out testing, samples are prepared with a common method implying melting polyamide-6 and an innovative method which allows the microdroplets formation by direct wetting in the reactive mixture. Conditions to obtain microdroplet in this new method are close to those of real size composite molding. First, this work focus on the verification of the new sample preparation method using 1 H and 13 C NMR to determine conversion rate and verify the presence of polyamide-6 on wetted fibres bundles. Contact angle are calculated to confirm the NMR analysis conclusions. Both of these analyses confirm that PA6 is effectively formed on fibres when wetting with the reactive mixture. Finally, interfacial shear strength is compared for both glass and high tenacity viscose with these two types of preparation procedures. Obtained values for glass fibres are τ = 25 ± 6 MPa with PA6-melting and τ = 20 ± 3 MPa with reactive mixture wetting. Reactive mixture wetting also allows to avoid high tenacity viscose degradation during PA6 formation, leading to the determination of the interfacial shear strength τ = 12 ± 3 MPa.

This study deals with the understanding of the sintering mechanisms that occur during consolidation of an ultra-high-performance polymer: poly(ether-ether-ketone). In particular, we investigated the effects of uniaxial pressure during spark plasma sintering (SPS) processing. Glass-transition temperature (T-g) measurements under loading, stress-strain curves and scanning electron microscopy analysis allowed us to determine the role of pressure intensity and temperature of application on macromolecular chain mobility in both the bulk and the surface of the particles. First, a loss of chain mobility in the bulk of the particles was observed under high pressure. Second, it was shown that high pressure applied at low temperature leads to friction effects between the particles which enhances chain mobility in the particle shell through a local melting phenomenon. These experimental conditions favor the healing of particles and high cohesion was then observed in the resulting sintered samples. The level of friction is enhanced when pressure is applied at a low temperature since the powders are still in a glassy state. Finally, the achievement of cohesive grain boundaries was found to be related to the location and conformation of chain ends. Good healing between particles can only occur if a sufficient number of chain ends are available at the surface of the particle shell. We showed that the native powder state plays a significant role. The direct use of as-received powder leads to final material exhibiting good cohesion whereas pretreatments of the native powder are highly detrimental. It should be noted that this processing does not affect the high initial degree of crystallinity because no bulk melting is observed during consolidation by sintering. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47645.

The objective of this work is to determine an adequate number of samples for an accurate prediction of tensile strength of fibres using a Weibull distribution. Theory will be compared to experimental results in order to know the effect of experimental errors on the theoretical expectations. The diameter and strength distribution of high tenacity viscose were evaluated. The chosen Weibull distribution was with two parameters. First, the best probability estimator for Weibull was determined using a random selection of experimental datas. Then, in order to be able to predict the number of sample knowing the variation of the Weibull modulus m, different relationship between the coefficient of variation of m and the number of sample n were tested. The relationship CV = 0.78/ $$\sqrt n$$ presented good agreement with experimental datas. The influence of the variation of m on the predicted value of strength was studied in order to determine an adequate number of sample to obtain limited variation of the predicted strength. The last part focus on experimental verification of the points previously developed. It was shown that it is possible to determine the influence of the variation of the Weibull modulus on the predicted strength. However, no correlation was found between the variations of the Weibull modulus and the error on the predicted strength.

International audience; The prior properties of recycled polypropylene depend on the origin of waste deposits and its chemical constituents. To obtain specific properties with a predefine melt flow index of polypropylene, the suppliers of polymer introduce additives and fillers. However, the addition of additives and/or fillers can modify strongly the mechanical behaviour of recycled polypropylene. To understand the impact of the additives and fillers on the quasi-static mechanical behaviour, we consider, in this study, three different recycled polypropylenes with three different melt flow index obtained from different waste deposits. The chemical constituents of the additives and filler contents of the recycled polypropylenes are determined through thermo-physico-chemical analysis. Tensile and bending tests performed at different strain rates allow identifying the mechanical properties such as the elastic modulus, the yield stress, the maximum stress, and the failure mechanisms. The results obtained are compared with non-recycled polypropylene and with few researches to explain the combined effect of additives. Finally, a post-mortem analysis of the samples was carried out to make the link between the obtained mechanical properties and microstructure.

The development of multilayered polymeric/metallic materials by a PM route employing spark plasma sintering (SPS) has been explored. The aim is to produce composites that join a polymer with a metal for structural applications. In a first approach, the consolidation of polyimide-based composites by SPS was studied. For temperatures as low as 350°C, homogeneous mechanical properties were achieved in compression tests. In a second set of experiments, multilayered polyimide/aluminium composites were consolidated by SPS. These polymer-based composites could be used as an interlayer material to join effectively polyimide and aluminium.

The mechanical properties of carbon fibers, especially their tensile properties, are affected by internal and surface defects. In order to asses in what extent the generation of surface defects can result in a loss of the mechanical properties, non-surface treated carbon fibers were oxidized with three different surface treatment processes: electro-chemical oxidation, oxidation in nitric acid, and oxidation in oxygen plasma. Different surface topographies and surface chemistries were obtained, as well as different types and densities of surface defects. The density of surface defects was measured with both a physical approach (Raman spectroscopy) and a chemical approach (Active Surface Area). The tensile properties were evaluated by determining the Weibull modulus and the scale parameter of each reference, after measuring the tensile strength for four different gauge lengths. A relationship between the tensile properties and the nature and density of surface defects was noticed, as large defects largely control the value of the tensile strength. When optimized, some oxidation surface treatment processes can generate surface functional groups as well as an increase of the mechanical properties of the fibers, because of the removal of the contamination layer of pyrolytic carbon generated during the carbonization of the polyacrylonitrile precursor. Oxidation in oxygen plasma revealed to be a promising technology for alternative surface treatment processes, as high levels of functionalization were achieved and a slight improvement of the mechanical properties was obtained too.

International audience; The increasing use of adhesives in industry has boosted the search for tests which allow the adherence level to be defined. These tests, depending on the type of load, examine different stresses, failure modes and mixed modes. Furthermore, these tests can be focused either on initiation or propagation of adhesive failure. The subject of this study is the initiation of adhesive failure. The initiation of failure can be determined with the 3-point bending test. Trials of 3-point bending tests were conducted on an aluminum 2024 substrate, with two different thicknesses, in order to understand the impact of the adherend thickness. The aluminum substrate received different types of surface pre-treatment: acetone cleaning, hydrochloric acid etching or aminopropyltriethoxysilane coating. Two adhesives were used: the first one was a mixture of epoxy pre-polymer DGEBA and DETA amine, whereas the second was a commercially formulated adhesive, ELECOLIT 6604. The initiation of adhesive failure was obtained by 3-point bending test and verified with SEM analysis. The failure loads measured enabled the effect of surface treatment on adhesive failure to be revealed: the results indicate that the surface treatment with silane is the most efficient in comparison to hydrochloric acid etching and of course to the simple acetone degreasing. It was assumed that the scatter of the results obtained for each series is due to the variation of the “intrinsic” adherence between the adhesive and the substrate. Furthermore, it was noted that the failure loads for different substrate thicknesses cannot be compared due to the effect of the thickness: it was therefore not possible to simply compare results obtained for different thicknesses of the same substrate for a given substrate-adhesive system. The energy approach proposed in this study makes it possible. The energy requested to initiate the adhesive failure for a given system can then be known, whatever the initial geometry of the 3-point bending test is. However, it was also shown that the thickness of the substrate must be correctly chosen. A thick substrate increases the dispersion and a thin substrate may induce local unwelcome plastic strain. In conclusion, this study allows to define an energy criteria for adhesives failure initiation.

The present study deals with the consolidation of an ultra-high performance polymer, the poly(ether ether ketone) (PEEK), for structural applications, using the powder metallurgy (PM) way, and more precisely the Spark Plasma Sintering (SPS) processing. The effects of SPS parameters such as temperature, pressure, and dwell time on density and mechanical properties of PEEK were investigated via a Design of Experiments (DoE). A temperature of 250 °C, a pressure of 40 MPa, and a dwell time of 20 min have been identified as the optimal SPS process parameters. In these conditions, a density of 1.31 g/cm3 was reached and homogeneous mechanical properties in the volume determined by means of compression tests were found with a compressive modulus of 2.75 GPa, a yield strength of 134 MPa, and a maximum compressive strain of 43%. These results are better than those of commercial products obtained by injection molding. The pressure appears to be a significant parameter on PEEK properties and plays positive or negative roles according to the responses of DoE studied. To our knowledge, it is one of the first studies based on the application of the PM techniques for PEEK consolidation showing the possibility to process below its melting point. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44911.

International audience; The purpose of the present article is to evaluate the real fibre surface involved in the practical adhesion of a flax/epoxy system. The difference in practical adhesion evaluated by microbond tests between Hermes (τapp = 22.5 ± 1.5 MPa) and Electra (τapp = 13.2 ± 3.2 MPa) flax fibres varieties/epoxy systems could not be explained by their superficial surface chemistry evaluated by XPS. FTIR spectroscopy highlights a difference in biochemical composition and Laser Confocal microscopy evidences a resin penetration for the two flax fibres systems (1.7 ± 0.7 μm for Hermes and 2.2 ± 0.8 μm for Electra). Thus the effective surface or complex interphase will be by consequence the overall area where the resin and fibre are in contact, i.e. the entire area penetrated by resin.

Thiol functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix photo-cured by ultraviolet light via a thiol-ene reaction. As revealed by X-ray photoelectron spectroscopy, the grafting was achieved by a reaction between propylene sulfide and the hydroxyl groups located at the surface of the fiber, with the presence of triethylamine. A significant improvement of the interfacial shear strength, measured by a micromechanical test derived from the pull-out test, was obtained (+18%). Generating covalent bonding between the carbon fiber surface and a thermoset polymerizing through a radical mechanism by grafting a chain transfer agent seemed to be an efficient way to improve adhesion strength at the interface.

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

Non-rubber components (mainly proteins and lipids) in natural rubber (NR) play important roles for controlling the properties of NR. Crosslinking process creates intermolecular chemical bonds in order to obtain a three-dimensional network, resulting in more elastic rubber. Sulphur crosslinking is the most popular method and is applied in the present study. Two types of NR were prepared, namely, whole natural rubber (WNR) and purified natural rubber (PNR). PNR was deproteinized by centrifugation method and then acetone extraction. These rubbers were crosslinked by an efficient vulcanization (EV) system. They were cured for three curing times (1xt90, 2xt90, 3xt90) at 150°C. WNR presents shorter curing time than PNR because there are some phospholipids and proteins which are natural accelerators for curing reaction. The presence of non-rubber components seems to play a major role on crosslinking density and adhesion phenomenon for rubber/glass system. AFM images of WNR show more heterogeneity and roughness compared to PNR.

This paper describes the conditions for contact formation between soft elastic hemispheres and softelastic substrates micropatterned with pillars. These microstructured substrates were often proposed inthe two past decades for the control of adhesion. In this study the hexagonal micropillars are arranged inhexagonal arrays and the width L of the pillars as well as the distance D between the pillars (with L¼Dfor a sample) are both varied from one sample to another in order to keep the overall planar surfacefraction of the pillars constant. Additionally, two pillars of heights h¼4 mm and h¼16 mm are consideredhere. As expected from previous studies different contact morphologies are found as a function of theaspect ratio and the contact pressure. The contact may be formed (i) only at the top of the pillar, (ii) bothat the top and between the pillars, or (iii) simultaneously at the top of the pillars and in between thepillars at the centre of the contact for which the pressure is the highest. Unexpectedly it is shown in thislast case that the same contact morphology is obtained with the same pressure if the surface patternaspect ratio L/h is varied homothetically, suggesting a scale invariant behaviour of the contact formationbetween the hemisphere and the soft elastic micropatterned substrate.& 2013 Elsevier Ltd. All rights reserved.

Oxygen plasma was used to modify the surface properties of carbon fibers and their adhesion strength with an acrylate resin cured by electron beam. A characterization of the surface topography and the surface chemistry was carried out (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, and X-ray photoelectron spectroscopy). The topography remained unchanged. Regarding the surface chemistry, carboxylic acids, alcohols, lactones, and ethers were created and their location was at the outer surface of the fibers. A pull-out test was used to measure the adhesion strength with the acrylate resin cured by electron beam. For comparison, an isothermal UV curing was also investigated. The value of the interfacial shear strength was increased only in the case of UV curing. No improvement was observed with electron beam curing, which highlighted the generation of an interphase, the mechanical properties of which are dependent on the processing conditions.

The aim of this study was to analyze the effect of interfacial covalent bonds on the adhesive behavior of an elastomer, a crosslinked polydimethylsiloxane, and a glass substrate. These covalent bonds were created by applying to both materials an appropriate surface treatment by means of plasma polymerization. Adhesion measurements were carried out by analyzing the contact area between a rubber hemisphere and a flat rigid glass plate. The contact was forced under a given compressive loading for different times tc, then the load was removed and the fracture propagation at the interface was recorded as a function of relaxation time tr. Finally, adhesion energies were also determined by means of a probe test using a tensile testing machine.

Although never emphasized and increasingly used in organic electronics, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)) layer-by-layer (lbl) film construction violates the alternation of polyanion and polycation rule stated as a prerequisit for a step-by-step film buildup. To demonstrate that this alternation is not always necessary, we studied the step-by-step construction of films using a single solution containing polycation/polyanion complexes. We investigated four different systems: PEDOT-PSS, bPEI-PSS (branched poly(ethylene imine)-poly(sodium 4-styrene sulfonate)), PDADMA-PSS (poly(diallyl dimethyl ammonium)-PSS), and PAH-PSS (poly(allylamine hydrochloride)-PSS). The film buildup obtained by spin-coating or dipping-and-drying process was monitored by ellipsometry, UV-vis-NIR spectrophotometry, and quartz-crystal microbalance. The surface morphology of the films was characterized by atomic force microscopy in tapping mode. After an initial transient regime, the different films have a linear buildup with the number of deposition steps. It appears that, when the particles composed of polyanion-polycation complex and complex aggregates in solution are more or less liquid (case of PEDOT-PSS and bPEI-PSS), our method leads to smooth films (roughness on the order of 1-2 nm). On the other hand, when these complexes are more or less solid particles (case of PDADMA-PSS and PAH-PSS), the resulting films are much rougher (typically 10 nm). Polycation/polyanion molar ratios in monomer unit of the liquid, rinsing, and drying steps are key parameters governing the film buildup process with an optimal polycation/polyanion molar ratio leading to the fastest film growth. This new and general lbl method, designated as 2-in-1 method, allows obtaining regular and controlled film buildup with a single liquid containing polyelectrolyte complexes and opens a new route for surface functionalization with polyelectrolytes. journal article research support, non-u.s. gov't 2012 Jun 12 2012 05 31 imported

Oxidized and non-oxidized carbon fibers were used to investigate the influence of an oxidation surface treatment on the adhesion strength with an acrylate resin cured by electron beam. For each type of fiber, a complete characterization of the surface properties was done (topography at a nanometric scale, specific surface area, X-ray photoelectron spectroscopy analysis and dispersive and polar components of the surface energy). The adhesion strength was measured by a pull-out test. For comparison, an isothermal UV curing of the matrix was also investigated. The value of the interfacial shear strength, determined by Greszczuk's model, was increased by the oxidation of the carbon fiber surface in the case of UV curing. In the case of electron beam curing, low values were obtained for both types of fibers, which could be explained by an incomplete cure of the matrix at the interface.

Two different commercial references of oxidized carbon fibers were used to investigate the influence of different oxidation surface treatments on the interfacial adhesion with an acrylate resin cured by electron beam. For each type of fiber, a characterization of the topography and the chemistry of the surface was done. The 90° flexural strength of unidirectional composites was measured in order to assess interfacial adhesion. Low values were obtained for both types of fibers, which could be explained by the creation of a weak interphase, which was highlighted by a dramatic improvement of the flexural strength after a post-cure. That interphase could be the origin of the low transverse mechanical properties of electron beam cured composites.

In this study, a new way to synthesize polypyrrole films is presented. This original way consists in the electropolymerization of polypyrrole under high frequency ultrasonic irradiation on conductive fluorine-doped tin oxide surfaces. The polypyrrole films obtained are then compared, in terms of chemical structure and morphology, to polypyrrole films synthesized by standard electrochemical methodology. Next, these polymer films are tested as an alternative to biomaterials that are commonly used as cell culture substrates. Thus, the adhesion and growth of osteoblastics cells and microbial cells on polymer-modified surfaces are investigated by using qualitative observation and quantitative tests. These studies proved the non-toxicity of the polymer films for osteoblastic and microbial cells but also a different behaviour of osteoblastic cells and microbial cells with polypyrrole films.

Three types of cotton fibers of different varieties and exhibiting different maturities and wax contents were examined by inverse gas chromatography (IGC), at infinite dilution. In this study, the potential relationships between the microstructure and the surface properties of different cotton fibers are analyzed. This method is based on the analysis of adsorption of gaseous probes on solid surfaces. By measuring the retention time of probes into a column containing the fibers, thermodynamic surface characteristics of these fibers, in particular the dispersive component of their surface energy, and their surface morphological aspects, are determined. The IGC data are correlated with a surface physico-chemical analysis performed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy.

Rubber blends of synthetic polyisoprene rubber (IR) and hydrogenated acrylonitrile butadiene rubber (HNBR) are prepared with different compositions. First, DSC results confirm that IR and HNBR are incompatible rubbers. A tensile testing machine equipped with a tack probe test allows us to measure the level of adhesion at rubber blends/glass as well as rubber blends/pure rubber interfaces, for contact times ranging from 0.1 s to a few hours. The adhesive properties of rubber blends were compared with those of pure rubbers. Adhesion energy G of IR/HNBR blends onto glass increases with the IR content in disagreement with a simple law of mixtures because of the influence of bulk properties of blends (morphology and mechanical behaviour). For a given blend, G increases with contact time certainly due to an interfacial reorganisation. Self-adhesion energies G S of pure rubbers and IR/HNBR blends increase also with contact time, thanks to mainly an interdiffusion phenomenon of the rubber chains through the interface. Self-adhesion energy of blends in contact with pure IR follows a simple law of mixtures as a function of IR content. On the contrary, the variation of self-adhesion energy of these blends in contact with pure HNBR is more complex.

The morphology of rubber blends was studied by means of confocal Raman spectroscopy, this latter being used as an imaging tool. Two immiscible rubbers were blended at different concentrations to test the ability of Raman spectroscopy for analysing a three-dimensional (3D) heterogeneous structure. These rubbers exhibited distinct vibrational signatures allowing us to identify them unambiguously. The samples were analysed as a function of depth (Z-axis) by modifying the focus of laser beam from Raman microscope. For each given value of depth Z, a flat surface was scanned in both X and Y directions. Thus, three-dimensional images were built by using a homemade software. The results obtained by Raman spectroscopy were compared to those stemming from scanning electron microscopy (SEM). This study clearly showed that the identification of rubber phases and the morphology of rubber blends as a function of their composition can be assessed by Raman spectroscopy.

Natural rubber (NR), synthetic polyisoprene rubber (IR) and hydrogenated acrylonitrile butadiene rubber (HNBR) were crosslinked by electron beam irradiation at different doses. The adhesion (at rubber/glass interfaces) and self-adhesion (at rubber/rubber interfaces) energies of uncrosslinked and weakly crosslinked rubbers were measured at contact times ranging from 0.1 s to a few hours by means of a tensile testing machine equipped with a tack-probe test. General relationships between these energies and the average molar mass between crosslinks were established in each case.

The purpose of this study was to better understand the effect of non-rubber substances (mainly proteins and lipids) on adhesion (against glasses) and self-adhesion tack properties of uncrosslinked natural rubber (NR). Various types of NR, with or without non-rubber constituents, were prepared. Synthetic polyisoprene rubber was also used as a reference material. All the rubbers were first characterized by many techniques (FT-IR, DSC, GPC, etc.). Two experimental tests were specially utilized to measure the level of adhesion and self-adhesion: (i) at very short contact times (from a few milliseconds up to 0.1 s) the impact of a pendulum and (ii) for longer contact times (from 0.1 s to a few h) the contact of a probe using a tensile testing machine. The tack energy increased with contact time for all the rubbers studied. Natural rubber which did not contain proteins and lipids exhibited the highest adhesion and self-adhesion tack abilities. In contrast, whole natural rubber, containing both proteins and lipi...

Composites have emerged as a valuable class of engineering materials because they offer many attributes not attainable with other materials. Their light weights coupled with high stiffness characteristics and selectable properties have fostered their use for many years in satellites, high-performance aircraft, world-class sailboats, and even submarines.4,5 Now these materials demonstrate their worth in the mundane but equally demanding consumer, infrastructure, and sporting goods arenas.

Bio-Based Composites: An Introduction Rungsima Chollakup, Wirasak Smitthipong, and Michel Nardin Bio-Based Strategy: Food and Non-Food Markets Rina Singh, Brent Erickson, and Paul Winters Strategy of Bio-Based Resources: Material versus Energy Kuakoon Piyachomkwan, Sittichoke Wanlapatit, Wirasak Smitthipong, and Klanarong Sriroth Bio-Inspired Materials Arkadiusz Chworos and Wirasak Smitthipong Natural Fiber Surface Treatments and Coupling Agents in Bio-Based Composites Potjanart Suwanruji, Wirasak Smitthipong, and Rungsima Chollakup Reinforcement of Polymers by Flax Fibers: Role of Interfaces Christophe Baley, Antoine Le Duigou, Alain Bourmaud, Peter Davies, Michel Nardin, and Claudine Morvan Effects of Reinforcing Fillers and Coupling Agents on Performances of Wood-Polymer Composites Diene Ndiaye, Mamadou Gueye, Ansou Malang Badji, Coumba Thiandoume, Anicet Dasylva, and Adams Tidjani Natural Fiber Polyolefin Composites: Processing, Melt Rheology, and Properties Haroutioun Askanian, Ya Feng, Sophie Commereuc, Florence Delor-Jestin, Kristyna Montagova, Roman Cermak, Valerie Massardier, and Vincent Verney Polysaccharide Bio-Based Composites: Nanofiber Fabrication and Application Jackapon Sunthonrvarabhas, Klanarong Sriroth, and Hyun-Joong Kim Recent Advances in Cellulose Nanocomposites Ali Faghihnejad and Hongbo Zeng Improvement of Damage Resilience of Composites Jiye Chen Lifetime Durability of Bio-Based Composites Vincent Verney, Solene Gaudin, Sophie Commereuc, Haroutioun Askanian, Florence Delor-Jestin, Alexandre Govin, and Rene Guyonnet Mechanical Properties of Natural Fiber-Reinforced Composites Rattana Tantatherdtam, Rungsima Chollakup, and Wirasak Smitthipong Characterization and Strength Modeling of Laminated Bio-Based Composites Peggi L. Clouston, Sanjay R. Arwade, and Alireza Amini Micromechanical Modeling of Bio-Based Composites Michael May and Deborah Mohrmann Life Cycle Assessments of Bio-Based Composites: A Review Thimothy Thamae and Caroline Baillie Bio-Based Composites: Future Trends and Environmental Aspects V.P. Sharma

The present study deals with the optimization of polyimide (PI) mechanical properties, obtained by Spark Plasma Sintering (SPS), by using a method combining Design of Experiments (DOE) with physical, structural, and mechanical characterizations. The effects of SPS parameters such as temperature, pressure, dwell time, and cooling rate on the density, mechanical properties, and structure of PI were investigated. The experimental results revealed that the mechanical properties of the material were optimized by raising the sintering temperature up to 350 degrees C. The optimized SPS processing parameters were a temperature of 350 degrees C, a pressure of 40 MPa, and a dwell time of 5 min. Under these conditions, a relative density of 99.6% was reached within only a few minutes. The corresponding mechanical properties consisted of Young's modulus of 3.43 GPa, a Shore D hardness of 87.3, and a compressive strength of 738 MPa for a maximum compressive strain of 61.8%. Moreover, when working at 320 degrees C and at 100 MPa, an increase in the dwell time was necessary to enhance the properties. Contrary to the other parameters, the cooling rate appeared to be a non-significant parameter. Finally, correlations between the PI structure and the mechanical properties were made to demonstrate the densification mechanisms. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41542.

In this work, we discuss quantitatively two basic relations describing the wetting behavior of microtopo- graphically patterned substrates. Each of them contains scale invariant topographical parameters that can be easily expressed onto substrates decorated with specifically designed micro- pillars. The first relation discussed in this paper describes the contact angle hysteresis of water droplets in the Cassie−Baxter regime. It is shown that the energy at the origin of the hysteresis, that has to be overcome for moving the triple line, can be invariantly expressed for hexagonal pillars by varying the pillars width and interpillar distance. Identical contact angle hystereses are thus measured on substrates expressing this scale invariance for pillar widths and interpillar distances ranging from 4 to 128 μm. The second relation we discuss concerns the faceting of droplets spreading on microtopographically patterned substrates. It is shown in this case that the condition for pinning of the triple line can be fulfilled by simultaneously varying the height of the pillars and the interpillar distance, leading to faceted droplets of similar morphologies. The invariance of these two wetting phenomena resulting from the simultaneous and homothetic variation of topographical parameters is demonstrated for a wide range of pattern dimensions. Our results show that either of those two wetting behaviors can be simply achieved by the proper choice of a dimensionless ratio of topographical length scales.

This article presents two high-temperature thermoplastic powders which were sintered by spark plasma sintering in order to get homogeneous mechanical properties. Dense polyimide (PI) and polyetheretherketone (PEEK) specimens were obtained at temperatures as low as 320°C for PI and 200°C for PEEK, respectively. Relative densities higher than 99% were reached for both materials. In order to characterize their properties, in situ measurements with compression and hardness tests were carried out on sintered samples. This method allowed to obtain polymeric materials with improved mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40783.

Maleic anhydride plasma polymer was deposited at the surface of carbon fibers and functionalized with vinyl and thiol groups to improve its adhesion strength with an acrylate matrix cured by an electron beam. A characterization of the fiber surface properties was done before and after coating (topography, surface chemistry, and surface energy). Sharp improvements of the interfacial shear strength (+ 120%), measured by a micromechanical test derived from the pull-out test, were obtained and, to the best of our knowledge, never reported before. The values were close to the ones obtained with a thermal cure. The comparison of this approach with other types of surface treatments (oxidation, grafting of coupling agents) enabled the establishment of a general strategy for the improvement of the interfacial adhesion in carbon fiber composites cured by an electron beam and potentially the improvement of their mechanical properties. This strategy is based on a high surface density of functionalities that are generating covalent bonding during the polymerization of the matrix and on the insertion of a polymer layer strongly attached to the fiber surface and acting as a buffer between the fiber surface and the matrix to counteract the generation of stress in the interphase.

Capillary rise experiments of different liquids in glass capillaries and in columns of packed powders were carried out. The analysis of this rise was performed according to the classical Washburn’s equation in which the calculation of a constant term is needed in order to be able to determine contact angle of the considered liquid on the capillary wall or powders. However, it was observed that this constant term apparently varies as a function of the liquid used, in contradiction with Washburn’s approach. A more fundamental study of alkane rise into glass capillaries was carried out showing that this apparent variation is due to the variation of contact angles, which can take large values (up to 60°) as a function of velocity of the liquid front, although their expected value is 0°. Therefore, in the case of powders, different approaches to determine the real constant term with respect to particle size are proposed. Consequently, the use of Washburn’s equation for the determination of contact angles of liquids on these powders is also discussed.

This study investigates the adhesion, cytoskeletal changes, and resorptive activity of disaggregated rat osteoclasts cultured on polished slices of three biomaterials: crystalline synthetic hydroxyapatite (HA), carbonated hydroxyapatite (C-HA), and natural calcium carbonate (C). The surface chemistry of each substrate was defined by X-ray diffraction and IR spectroscopy, surface wettability by the dispersive, and the polar components of the surface energies. Osteoclast adhesion was modulated by the polar component of the surface energy: fewer (p < 0.01) osteoclasts adhered to C-HA (97 +/- 20/slice, surface energy 9 +/- 5 mJ/m2) than to HA (234 +/- 16/slice, surface energy 44 +/- 2 mJ/m2) or to C (268 +/- 37/slice, surface energy 58 +/- 0.5 mJ/m2). Actin rings, which are the cytoskeletal structure essential for resorption, developed on all three materials. The area of the actin ring, which is resorbed by local acidification, and the osteoclast area, which reflects osteoclast spreading, were both greater in osteoclasts cultured on HA and C-HA than in those cultured on C. C was resorbed, but HA and C-HA were not. Thus, the surface energy plays an essential role in osteoclast adhesion, whereas osteoclast spreading may depend on the surface chemistry, especially on protein adsorption and/or on newly formed apatite layers. Resorption may be limited to the solubility of the biomaterial.

Specific interactions in binary blends of ethylene-vinylacetate copolymer (EVA) with various low molecular weight terpene-phenol tackifying resins (TPR) were systematically investigated, as a function of the composition of the blend and of the electron-acceptor ability of the resin, using attenuated total reflection Fourier transform IR (ATR-FTi.r.) spectroscopy. Molecular acid—base complexes (according to Lewis' electron acceptor—donor concepts) were evidenced between TPR hydroxyl groups and EVA carbonyl groups. Quantitative information on the fraction of acid—base bonded entities, the enthalpy and the equilibrium constant of pair formation were obtained. It appears that the amorphous phases of such polymer blends remain thermodynamically miscible whatever the composition of the blend and the resin acidity. On the contrary, a crystalline transition of the EVA copolymer is observed, depending on the blend composition and resin acidity. This transition is discussed in terms of enthalpy and entropy considerations based on FTi.r. and differential scanning calorimetry (DSC) investigations. Fundamental results are then summarized in order to predict the melting enthalpy of a polymer blend.

Naphthalene-based mesophase ribbon fibres were studied in the present work. The fibres were surface treated in a plasma reactor and their mechanical and surface characteristics determined before and after the surface oxidation. The dispersive and non-dispersive components of the surface energy were obtained by contact angle measurements using a tensiometric method, and the surface oxygen content was measured by XPS. The mechanical characterisation was made by single filament tensile tests. The interactions between the ribbon fibres and a polycarbonate matrix were assessed by means of fragmentation tests. The results were compared with those obtained with pitch-based fibres with circular cross-sections.

Thermal characteristics of ethylene—vinylacetate (EVA) copolymers having vinylacetate contents ranging from 5 to 40 w/w % are studied by differential scanning calorimetry. It is first shown that EVA copolymers having a vinylacetate content lower than 30 w/w % obey the Flory and Burfield theories of copolymer crystallisation. The minimum sequence length of CH2 ethylenic entities required to participate in a crystalline lamella is also deduced. One can conclude that EVA copolymers represent cases of “total exclusion” of the noncrystallizable comonomer. Moreover, it is observed that when the vinylacetate content is increased, the relative quantity of polyethylene amorphous phase increases and the degree of crystallinity decreases; whereas the β transition temperature of a characteristic-oriented amorphous phase is kept constant. A phase model of ethylene-vinylacetate copolymers, based on an enrichment process of the interlamellar amorphous phase by polyethylene segments originating from the crystalline phase, at increasing vinylacetate content, is proposed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1903–1912, 1997

The acoustic analysis of the morphological evolution, from the surface to the bulk, of a vinylester resin cured in contact with two types of surfaces, i.e. aluminium and air, has been studied. The analysis was also performed as a function of styrene monomer content of the uncured resin. The existence of a thick layer, in which the vinylester network is deeply affected due to the relative variations of polystyrene and vinylester polymer from the interface to the bulk, was first demonstrated by microscopical Fourier transform-infrared spectroscopy. Secondly, this structural evolution was analysed by means of an acoustic scan technique, allowing the variations of the mechanical properties of the vinylester network to be estimated as a function of the distance from the interface. A good correlation was obtained between spectroscopic and acoustic results.

This paper deals with the analysis of peel energy of assemblies measured in different environments, i.e. in air and in the presence of liquids, and constitutes a brief review of the work of Professor Schultz' team in this domain. It is shown how such measurements can lead to a better knowledge of the nature as well as of the magnitude of fundamental interactions established at the interface between two solids. Earlier experiments have shown that peel energy can be expressed as a product of three terms corresponding, respectively, to the reversible energy of interfacial adhesion, the hysteretic losses of the bulk materials and the molecular dissipation near the crack front during peeling. This approach is well-verified when only physical interactions (van der Waals) are involved at the interface. However, more complex cases correspond to systems where specific interactions are also established between both materials, in particular acid-base interactions and creation of chemical bonds. In both case...

In previous work concerning fiber−matrix junctions in single-fiber composites, a linear relationship has been established between the interfacial shear strength τ and the reversible adhesion energy W at the interface, which takes into account dispersive and acid−base interactions. In the present study, the validity of such a relationship is examined from a theoretical point of view. It appears that its mathematical form is entirely justified in terms of “static friction”, if τ is considered as the resistance to the interfacial slipping due to the existence of molecular interactions. The most important parameter in this approach appears to be the equilibrium intermolecular or interatomic distance λ at the interface. It is shown, in good agreement with results available in the literature, that λ decreases when the work of adhesion increases, in particular when strong acid−base interactions are involved at the interface. To a first approximation, it appears that the reversible work of adhesion W varies like ...

This paper deals with the influence of interphase formation on the stress transfer capacity of the fibre-matrix interface in single fibre composites and constitutes a brief review of our recent work. This influence is studied through the deviation of the experimental results from a recent theoretical analysis relating the interfacial shear strength to the reversible work of adhesion established between the fibre and the matrix. Two examples of interphases are considered: a transcrystalline layer in carbon fibre-PEEK composites and a pseudo-glassy interphase in carbon fibre-elastomer systems. In the former case, the low transverse mechanical properties of the transcrystalline layer lead to a decrease of the interfacial shear strength, whereas, in the latter case, the glassy behaviour of the interphase explains the improved interfacial stress transfer capacity.

The effect on the peeling energy, G, of glass/styrene-butadiene rubber (SBR) assemblies of the length, N, of the alkyl chain, ranging from 4 to 30 carbon atoms, of silane coupling agents is determined. Experimentally, it is shown that G strongly increases with N. Therefore, considering that the rheological model of adhesion (or model of multiplying factors) is valid, G is assumed equal to the product of three terms: the reversible adhesion energy, W. at the interface, the viscoelastic dissipation factor, φ, of SBR and a “molecular factor” to be determined. Finally, it appears that this latter factor depends linearly on N. Such a result should be consistent with an extraction (“suction”) process of the silane alkyl links from bulk SBR during peeling experiments.

The stress transfer capacity of carbon fibre-SBR interfaces is analysed in terms of interfacial shear strength and measured by means of a fragmentation test on single fibre composites. For all the cases studied, the experimental values of the interfacial shear strength are largely higher than theoretically expected. Such a result is explained by the existence near the fibre surface of an interfacial layer in which the polymer chain mobility is greatly reduced. Such an interfacial region of low mobility is pointed out by mechanical spectrometry on unidirectional composites at different fibre contents. This interphase could exhibit a pseudo-glassy behaviour and, in particular, an elastic modulus close to that of the elastomer in its glassy state whatever the temperature.

A round-robin programme has been undertaken to assess the compatibility in the micromechanical techniques used to evaluate the interfacial shear strength of the fibre/matrix bond in composite materials. The tests selected for evaluation were the single-fibre pull-out test, the microdebond test, the fragmentation test and the micro-indentation test. Twelve laboratories were invited to participate in this programme. Each laboratory was supplied with Caurtaulds XA fibre in the untreated condition and with a standard surface treatment, and a quantity of epoxy resin, hardener and catalyst, all from the same batch. Some laboratories were supplied with composite bars made with the same materials. A common cure cycle was chosen for sample preparation. Each laboratory conducted the tests to its own procedures. The results showed that the scatter within each laboratory was acceptable but the scatter between laboratories for a particular test was high. The results are discussed and possible explanations are presented for these observations. The indications are that the fundamental procedures used in each laboratory are sound. The results also suggest that there is great potential for achieving standard procedures and reducing the inter-laboratory scatter. A further round-robin programme is proposed to generate test protocols.

International audience; Polyethyleneimine films have been deposited on platinum electrode surfaces by electrochemical oxidation of ethylenediamine H2N-CH2-CH2-NH2 (EDA) in acetonitrile solutions. This electrochemical synthesis was realized by cyclic voltammetry and gravimetry techniques. Then, the characterization of the thin solid polyethyleneimine film was performed using X-ray photoelectron spectroscopy and infrared spectroscopy. It was also shown, using atomic force microscopy, that the solid polymeric coating has a granular and homogeneous structure. The influence of EDA concentration on the electropolymerization process was studied leading to the conclusion that the reaction is easier for high EDA concentration. Then, the influence of the nature and concentration of the supporting salt was investigated, showing that its nature is not very important, contrary to its concentration.

The stress transfer from the matrix to the fibre in composite materials depends to a large extent on the level of adhesion between these materials. In the present study, the work of adhesion between carbon fibres and PEEK polymer is estimated from the surface characteristics of the fibre and the matrix and, more precisely, from the dispersive component of the surface energy and the acid–base character of both material, determined by inverse gas chromatography at infinite dilution. The interfacial shear strength at the carbon fibre/PEEK interface is measured also by means of a fragmentation test on the respective single-fibre composites. For PEEK polymer, it is shown that the acid–base characteristic of fibres and powder are different, indicating that the orientation of the macromolecules near the surface may be affected by the processing of such materials. Nevertheless, as already shown in previous studies for other systems, a linear relationship between the interfacial shear strength and the adhesion at the fibre/matrix interface can be established.