Bioactive chitosan/polydopamine nanospheres coating on carbon fiber towards strengthening epoxy composites.

This paper initially examines the feasibility and effectiveness on interfacial adhesion of composites when grafting nanoparticle-structured polydopamine (PDA) and chitosan around carbon fiber periphery. The resulting interfacial shear strength was maximized as 92.3 MPa, delivering 50.1 % and 15.7-16.2 % gains over those of control fiber and only polydopamine nanospheres (PDANPs) or only chitosan modified fiber composites. Measuring surface morphology and thermal stability of fibers found that abundant PDANPs well adhered with the help of chitosan, highlighting nanoscale size effects and intrinsic adhesiveness of PDA. Under good wettability, rich and dense interfacial interactions (covalent and hydrogen bond, electrostatic interaction, and π conjugation) caused by PDANPs/chitosan coating provides impetus for effective stress transfer. Additionally, the stable "soft-rigid" combination of chitosan and PDANPs adds the efficiency of crack passivation. As such, it is hoped that this work could fully explore the possibility of PDA geometry in interphase engineering of fiber composites.

Strong, bacteriostatic and transparent polylactic acid-based composites by incorporating quaternary ammonium cellulose nanocrystals.

Renewable natural fibers (e.g., cellulose nanocrystals (CNCs)) are being applied for reinforcing bio-based polylactic acid (PLA). For improvement in the interfacial compatibility between CNCs and PLA and the dispersibility of CNCs, a quaternary ammonium salt-coated CNCs (Q-CNCs) hybrid was prepared in this study based on an esterification self-polymerization method, and such hybrid was further utilized as a new strengthening/toughening nanofiller for producing the Q-CNCs-reinforced PLA composite. The results confirmed that quaternary ammonium salt coatings could efficiently enhance CNCs/PLA interfacial compatibility via mechanical interlocking and semi-interpenetrating networks. Attributing to the synergistic effect of quaternary ammonium salts and CNCs, a considerable enhancement in processing, mechanical, and thermal properties was gained in the obtained Q-CNCs-reinforced PLA composite. With the addition of 0.5 wt% Q-CNCs, the tensile strength, Young's modulus, and elongation at break of the Q-CNCs-reinforced PLA composite was raised by approximately 23 %, 37 % and 18 %, respectively; compared with pure PLA, the obtained composite had excellent bacteriostatic properties and good transparency. This work discusses the development of high-performance, low-cost and sustainable PLA-based composites on a potential application in packaging materials.

Assessment of electrical conductivity of polymer nanocomposites containing a deficient interphase around graphene nanosheet.

In this study, a poor/imperfect interphase is assumed to express the effective interphase thickness, operative filler concentration, percolation onset and volume share of network in graphene-polymer systems. Additionally, a conventional model is advanced by the mentioned terms for conductivity of samples by the extent of conduction transference between graphene and polymer medium. The model predictions are linked to the experimented data. Likewise, the mentioned terms as well as the conductivity of nanocomposites are expressed at dissimilar ranges of various factors. The novel equations successfully predict the percolation onset and conductivity in the samples containing a poor/imperfect interphase. Thin and long nanosheets with high conduction transportation desirably govern the percolation onset and nanocomposite conductivity, but a bigger tunneling distance causes a lower conductivity.

Improving interfacial shear strength of fique fibres using an acrylic coating.

Natural fibres have proven to be a potential alternative to replace synthetic fibres in some composite materials applications. However, drawbacks such as impregnation difficulties and the poor fibre-matrix interface limit the use of natural fibres in high-performance applications. This work proposes using an acrylic resin to coat the fibre surface to enhance the interfacial compatibility among fique fibres and polyester resin. Pull-out tests revealed an improvement in the interfacial shear strength of about 110% for coated fibres. Furthermore, nanoindentation test, Micro Raman spectroscopy and scanning electronic microscopy indicated that the acrylic resin eliminates the gap at the fibre/matrix interface seen in the uncoated fibres. Observed behaviour could be attributed to a better chemical bonding between the fibre and matrix and is also hypothesised that the elastic characteristic of the coating helps to transfer loads effectively from the matrix to the fibre.

Novel Functionalized Boron Nitride Nanosheets Achieved by Radiation-Induced Oxygen Radicals and Their Enhancement for Polymer Nanocomposites.

Boron nitride nanosheets (BNNSs) exfoliated from hexagonal boron nitride (h-BN) show great potential in polymer-based composites due to their excellent mechanical properties, highly thermal conductivity, and insulation properties. Moreover, the structural optimization, especially the surface hydroxylation, of BNNSs is of importance to promote their reinforcements and optimize the compatibility of its polymer matrix. In this work, BNNSs were successfully attracted by oxygen radicals decomposed from di-tert-butylperoxide (TBP) induced by electron beam irradiation and then treated with piranha solution. The structural changes of BNNSs in the modification process were deeply studied, and the results demonstrate that the as-prepared covalently functionalized BNNSs possess abundant surface hydroxyl groups as well as reliable structural integrity. Of particular importance is that the yield rate of the hydroxyl groups is impressive, whereas the usage of organic peroxide and reaction time is greatly reduced due to the positive effect of the electron beam irradiation. The comparisons of PVA/BNNSs nanocomposites further indicate that the hydroxyl-functionalized BNNSs effectively promote mechanical properties and breakdown strength due to the enhanced compatibility and strong two-phase interactions between nanofillers and the polymer matrix, which further verify the application prospects of the novel route proposed in this work.

Detecting Microstructural Criticality/Degeneracy through Hybrid Learning Strategies Trained by Molecular Dynamics Simulations.

Efficient microstructure design can strongly accelerate the development of materials. However, the complexity of the microstructure-behavior relation renders the criticalities and degeneracies within the microstructure space highly possible. Criticality means that a slight microstructural change can lead to a dramatic transition in material behavior, while degeneracy means that very different microstructures may lead to similar behaviors. To investigate these microstructural characteristics of the fiber/matrix interface within composite materials, we have proposed a hybrid deep-learning-based framework by integrating the supervised feed-forward neural network and the unsupervised autoencoder, which are trained by the molecular dynamics (MD) simulation results. The well-trained model continuously maps the elemental density images within the interfacial area into a low-dimensional latent space. Assisted by the extracted latent features, we can easily detect the criticalities and degeneracies within the original microstructure space of the composite's interface. The predicted microstructural criticalities and degeneracies are validated by investigating their atomistic origins through MD simulations. The proposed framework can be employed for the interfacial microstructure design of composite materials by identifying certain interfacial microstructures that might lead to undesirable behaviors.

Improvement of Interfacial Properties and Bioactivity of CF/PEEK Composites by Rapid Biomineralization of Hydroxyapatite.

The carbon fiber/hydroxyapatite (CF/HA) reinforcement with a three-dimensional flower-like structure was rapidly fabricated with the biomimetic mineralization method to strengthen the interfacial performance and bioactivity of carbon fiber/polyether ether ketone (CF/PEEK) composites. Silk fibroin (SF), which can construct a robust interphase between CF and PEEK, supported an organic template to regulate the growth of inorganic HA. The interfacial properties were markedly enhanced through mechanical interlocking and interface adhesion induced by increasing roughness and surface energy of CF. Besides, the mineralization time was significantly reduced after the addition of cetyltrimethylammonium bromide to the simulated body fluid, and the prepared CF/HA possessed good bioactivity. In this study, the interlaminar shear strength (ILSS) and flexural strength of CF-HA/45/PEEK composites demonstrated an enhancement of 45.9% and 51.2%, respectively, compared to the untreated CF/PEEK composites. It is predicted that this strategy could provide a rapid and convenient route to ameliorate the interfacial performance and bioactivity of CF/PEEK composites simultaneously.

Hierarchical Flax Fibers by ZnO Electroless Deposition: Tailoring the Natural Fibers/Synthetic Matrix Interphase in Composites.

Hierarchical functionalization of flax fibers with ZnO nanostructures was achieved by electroless deposition to improve the interfacial adhesion between the natural fibers and synthetic matrix in composite materials. The structural, morphological, thermal and wetting properties of the pristine and ZnO-coated flax fibers were investigated. Thus, the ZnO-coated flax fabric discloses an apparent contact angle of ~140° immediately after the placement of a water droplet on its surface. An assessment of the interfacial adhesion at the yarn scale was also carried out on the flax yarns coated with ZnO nanostructures. Thus, after the ZnO functionalization process, no significant degradation of the tensile properties of the flax yarns occurs. Furthermore, the single yarn fragmentation tests revealed a notable increase in the interfacial adhesion with an epoxy matrix, reductions of 36% and 9% in debonding and critical length values being measured compared to those of the pristine flax yarns, respectively. The analysis of the fracture morphology by scanning electron microscopy and X-ray microtomography highlighted the positive role of ZnO nanostructures in restraining debonding phenomena at the flax fibers/epoxy resin matrix interphase.

Push-Out Method for Micro Measurements of Interfacial Strength in Aluminium Alloy Matrix Composites.

The main goal of this work was the evaluation of the interfacial strength of the carbon fibres/aluminium matrix interface dependently on the utilised composite fabrication method, namely high pressure die casting and gas pressure infiltration. In addition, the influence of a Ni-P coating on the C-fibres was investigated. The proposed measurements of the interfacial strength were carried out by means of the "push-out" method. The interfacial strength of the samples fabricated using the high-pressure infiltration method average between 19.03 MPa and 45.34 MPa.

In Situ Generation of Green Hybrid Nanofibrillar Polymer-Polymer Composites-A Novel Approach to the Triple Shape Memory Polymer Formation.

The paper discusses the possibility of using in situ generated hybrid polymer-polymer nanocomposites as polymeric materials with triple shape memory, which, unlike conventional polymer blends with triple shape memory, are characterized by fully separated phase transition temperatures and strongest bonding between the polymer blends phase interfaces which are critical to the shape fixing and recovery. This was demonstrated using the three-component system polylactide/polybutylene adipateterephthalate/cellulose nanofibers (PLA/PBAT/CNFs). The role of in situ generated PBAT nanofibers and CNFs in the formation of efficient physical crosslinks at PLA-PBAT, PLA-CNF and PBAT-CNF interfaces and the effect of CNFs on the PBAT fibrillation and crystallization processes were elucidated. The in situ generated composites showed drastically higher values of strain recovery ratios, strain fixity ratios, faster recovery rate and better mechanical properties compared to the blend.

Establishment of Silane/GO Multistage Hybrid Interface Layer to Improve Interfacial and Mechanical Properties of Carbon Fiber Reinforced Poly (phthalazinone ether ketone) Thermoplastic Composites.

This study focused on the faint interface bonding between carbon fiber (CF) and poly(phthalazinone ether ketone) (PPEK) thermoplastic, a multistage hybrid interface layer was constructed via the condensation reaction of N-[3-(Trimethoxysilyl)propyl]-N,N,N-trimethylammonium chloride (KHN+) and the electrostatic adsorption of graphene oxide (GO). The influence of the contents of GO (0.2 wt%, 0.4 wt%, 0.6 wt%) on the interfacial properties of composites was explored. FTIR, Raman spectra, XPS tests indicated the successful preparation of CF-KHN+-GO reinforcements. The multistage hybrid interface layer significantly increased fiber surface roughness without surface microstructure destruction. Simultaneously, polarity and wettability are remarkably improved as evidenced by the dynamic contact angle experiment. The interlaminar shear strength (ILSS) and flexural strength of the CF/PPEK composites with 0.4 wt% GO (CF-KHN+-4GO) were 74.57 and 1508 MPa, which was 25.2% and 23.5% higher than that of untreated CF/PPEK composite, respectively. Dynamic mechanical analysis proved that CF/GO/PPEK composites have excellent high-temperature mechanical properties. This study furnishes an unsophisticated and valid strategy to build an interface transition layer with a strong binding force, which would offer a new train of thought in preparing high-performing structural composites.

Effects of different "rigid-flexible" structures of carbon fibers surface on the interfacial microstructure and mechanical properties of carbon fiber/epoxy resin composites.

In order to comprehend the influence of different "rigid-flexible" structures on the interface strength of carbon fiber(CF)/epoxy composites, CNTs was firstly chemically grafted on CFs surface, and then polyamide (PA) was grafted onto CF-CNTs surface through varying anionic polymerization time of caprolactam [CF-CNTs-PAn (n = 6 h, 12 h, 24 h)]. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicated the successful establishment of CNTs and PA. TGA demonstrated the different grafting amounts of CF-CNTs-PAn (n = 6 h, 12 h and 24 h). SEM images revealed a compactness and uniform coverage of the CNTs/PA, with increasing polymerization time, the CF and CNTs surface was covered by a thick layer of PA. The surface energy increased and then decreased. The optimal interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the CF/epoxy composites with a polymerization time of 12 h (CF-CNTs-PA12h) was 86.7 and 85.4 MPa, which was 77.6% and 45.7% higher than that of untreated CF/epoxy composite. As the polymerization time grew, the impact toughness and tensile strength of CF/epoxy composites enhanced and conductivity of CF/epoxy composite reduced. In addition, the mechanisms of reinforcement and toughening were also illuminated. This work would provide a certain theoretical basis for the preparation and applications of high-performance CF composites with different structures.

Nondestructive Strategy to Effectively Enhance the Interfacial Adhesion of PBO/Epoxy Composites.

Low interfacial adhesion seriously limits the wide application of PBO fiber in composites. To solve this problem, a novel hierarchical reinforcement strategy was developed by introducing epoxy sizing, nanoreinforcement of amino-functionalized silicon dioxide (SiO2-NH2), and an interfacial compatibilizer of 2,6-bis(2-hydroxy-4-aminophenyl) benzobisoxazole (HABO) onto poly(p-phenylene benzobisoxazole) (PBO) fibers via a facile dip-coating approach. SiO2-NH2 and HABO were uniformly dispersed in epoxy sizing, forming an active interface layer. On this basis, wettability, surface roughness of the PBO fiber, and compatibility with the resin matrix were significantly improved, which gave 88.4 and 40.4% enhancement in the interfacial shear strength and interlaminar shear strength of the corresponding composites, respectively. Moreover, it should be noted that the outstanding mechanical and thermal properties of the PBO fiber were not impaired during the sizing treatment. In summary, our work provides an effective and damage-free approach to improve the interfacial adhesion of PBO/epoxy composites.

Environmentally Friendly Surface Modification Treatment of Flax Fibers by Supercritical Carbon Dioxide.

The present work investigates the effects of an environmentally friendly treatment based on supercritical carbon dioxide (scCO2) on the interfacial adhesion of flax fibers with thermoset matrices. In particular, the influence of this green treatment on the mechanical (by single yarn tensile test), thermal (by TGA), and chemical (by FT-IR) properties of commercially available flax yarns was preliminary addressed. Results showed that scCO2 can significantly modify the biochemical composition of flax fibers, by selectively removing lignin and hemicellulose, without altering their thermal stability and, most importantly, their mechanical properties. Single yarn fragmentation test results highlighted an increased interfacial adhesion after scCO2 treatment, especially for the vinylester matrix, in terms of reduced debonding and critical fragment length values compared to the untreated yarns by 18.9% and 15.1%, respectively. The treatment was less effective for epoxy matrix, for which debonding and critical fragment length values were reduced to a lesser extent, by 3.4% and 3.7%, respectively.

Strengthening and Toughening of Polylactide/Sisal Fiber Biocomposites via in-situ Reaction with Epoxy-Functionalized Oligomer and Poly (butylene-adipate-terephthalate).

With the addition of poly (butylene-adipate-terephthalate) (PBAT) and a commercial grade epoxy-functionalized oligomer Joncryl ADR@-4368 (ADR), a blend of polylactic acid (PLA) and sisal fibers (SF) were melt-prepared via in-situ reactive process to improve the toughness and interfacial bonding of polylactide/sisal fiber composites. Fourier Transform infrared spectroscopy (FTIR) analysis demonstrated chemical bonding between sisal fibers and matrix, and scanning electron microscope characterization indicated the enhancement of interfacial adhesion between PLA matrix and sisal fibers. The micro-debonding test proved that the interfacial adhesion between PLA and SF was improved because of ADR. The presence of ADR behaved like a hinge among sisal fibers and matrix via an in-situ interfacial reaction, and compatibility between PLA and PBAT was also augmented. The introduction of PBAT exerted a plasticization effect on composites. Therefore, the toughness of PLA/SF composites was significantly elevated, while the tensile strength of composites could be well preserved. The paper focused on the demonstration of interfacial interaction and structure-properties relationship of the composites.

Plasma Nanocoatings Developed to Control the Shear Strength of Polymer Composites.

All reinforcements for polymer-matrix composites must be coated with a suitable material in the form of a thin film to improve compatibility and interfacial adhesion between the reinforcement and the polymer matrix. In this study, plasma nanotechnology was used to synthetize such functional nanocoatings using pure tetravinylsilane (TVS) and its mixtures with oxygen gas (O2) as precursors. The plasma-coated glass fibers (GFs) were unidirectionally embedded in a polyester resin to produce short composite beams that were analyzed by a short-beam-shear test to determine the shear strength characterizing the functionality of the nanocoatings in a GF/polyester composite. The developed plasma nanocoatings allowed controlling the shear strength between 26.2-44.1 MPa depending on deposition conditions, i.e., the radiofrequency (RF) power and the oxygen fraction in the TVS/O2 mixture. This range of shear strength appears to be sufficiently broad to be used in the design of composites.

Improved Mechanical Properties of Copoly(Phthalazinone Ether Sulphone)s Composites Reinforced by Multiscale Carbon Fibre/Graphene Oxide Reinforcements: A Step Closer to Industrial Production.

The properties of carbon fibre (CF) reinforced composites rely heavily on the fibre-matrix interface. To enhance the interfacial properties of CF/copoly(phthalazinone ether sulfone)s (PPBES) composites, a series of multiscale hybrid carbon fibre/graphene oxide (CF/GO) reinforcements were fabricated by a multistep deposition strategy. The optimal GO loading in hybrid fibres was investigated. Benefiting from the dilute GO aqueous solution and repeated deposition procedures, CF/GO (0.5%) shows a homogeneous distribution of GO on the hybrid fibre surface, which is confirmed by scanning electron microscopy, atomic force microscope, and X-ray photoelectron spectroscopy, thereby ensuring that its PPBES composite possesses the highest interlaminar shear strength (91.5 MPa) and flexural strength (1886 MPa) with 16.0% and 24.1% enhancements, respectively, compared to its non-reinforced counterpart. Moreover, the incorporation of GO into the interface is beneficial for the hydrothermal ageing resistance and thermo-mechanical properties of the hierarchical composite. This means that a mass production strategy for enhancing mechanical properties of CF/PPBES by regulating the fiber-matrix interface was developed.

Interface Bond Improvement of Sisal Fibre Reinforced Polylactide Composites with Added Epoxy Oligomer.

To improve the interfacial bonding of sisal fiber-reinforced polylactide biocomposites, polylactide (PLA) and sisal fibers (SF) were melt-blended to fabricate bio-based composites via in situ reactive interfacial compatibilization with addition of a commercial grade epoxy-functionalized oligomer Joncryl ADR@-4368 (ADR). The FTIR (Fourier Transform infrared spectroscopy) analysis and SEM (scanning electron microscope) characterization demonstrated that the PLA molecular chain was bonded to the fiber surface and the epoxy-functionalized oligomer played a hinge-like role between the sisal fibers and the PLA matrix, which resulted in improved interfacial adhesion between the fibers and the PLA matrix. The interfacial reaction and microstructures of composites were further investigated by thermal and rheological analyses, which indicated that the mobility of the PLA molecular chain in composites was restricted because of the introduction of the ADR oligomer, which in turn reflected the improved interfacial interaction between SF and the PLA matrix. These results were further justified with the calculation of activation energies of glass transition relaxation (∆Ea) by dynamic mechanical analysis. The mechanical properties of PLA/SF composites were simultaneously reinforced and toughened with the addition of ADR oligomer. The interfacial interaction and structure-properties relationship of the composites are the key points of this study.

Design of Electrically Conductive Structural Composites by Modulating Aligned CVD-Grown Carbon Nanotube Length on Glass Fibers.

Function-integration in glass fiber (GF) reinforced polymer composites is highly desired for developing lightweight structures and devices with improved performance and structural health monitoring. In this study, homogeneously aligned carbon nanotube (CNT) shell was in situ grafted on GF by chemical vapor deposition (CVD). It was demonstrated that the CNT shell thickness and weight fraction can be modulated by controlling the CVD conditions. The obtained hierarchical CNTs-GF/epoxy composites show highly improved electrical conductivity and thermo-mechanical and flexural properties. The composite through-plane and in-plane electrical conductivities increase from a quasi-isolator value to ∼3.5 and 100 S/m, respectively, when the weight fraction of CNTs grafted on GF fabric varies from 0% to 7%, respectively. Meanwhile, the composite storage modulus and flexural modulus and strength improve as high as 12%, 21%, and 26%, respectively, with 100% retention of the glass transition temperature. The reinforcing mechanisms are investigated by analyzing the composite microstructure and the interfacial adhesion and wetting properties of CNTs-GF hybrids. Moreover, the specific damage-related resistance variation characteristics could be employed to in situ monitor the structural health state of the composites. The outstanding electrical and structural properties of the CNTs-GF composites were due to the specific interfacial and interphase structures created by homogeneously grafting aligned CNTs on each GF of the fabric.

Effective dispersion and crosslinking in PVA/cellulose fiber biocomposites via solid-state mechanochemistry.

A mechanochemical approach to improve the dispersion and the degree of crosslinking between cellulose fiber and polymer matrix is presented herein to create high performance poly(vinyl alcohol) (PVA)/cellulose biocomposites in a solvent-free and catalyst-free system. During a pan-milling process, the hydrogen bonds in both cellulose and PVA were effectively broken up, and the released hydroxyl groups could react with succinic anhydride (SA) to form covalent bonds between the two components. This stress-induced chemical reaction was verified by fourier transform infrared spectroscopy. The reaction kinetics was discussed according to the conversion rate of SA during the pan-milling process. Soxhlet extraction with hot water showed that the crosslinked PVA/cellulose retained more PVA in the composites due to the homogeneous and heterogeneous crosslinking. Scanning electron microscope images indicated the dispersion and interfacial interactions between PVA and cellulose were largely improved. The resulting composites exhibited remarkably enhanced mechanical properties. The tensile strength increased from 8.8 MPa (without mechanochemical treatment) to 18.2 MPa, and elongation at break increased from 76.8 to 361.7% after the treatment. Their thermal stability was also significantly improved.