Interfacial structure analysis of polymer laminate using SPring-8 X-ray microbeam

Interfacial structure of laminated polyethylene (PE)/polypropylene (PP) films was investigated by synchrotron X-ray microbeam. The X-ray microbeam (0.9 μm (vertical) × 1.7 μm (horizontal)) formed using a phase zone plate was irradiated on the cross-section of the laminated films. In order to irradiate X-ray microbeam in the direction perpendicular to the cross-section of the film sample, adjustment of the sample setting was performed by Thomson scattering method. The Thomson scattering intensity is proportional to the number of the irradiated electrons, so the irradiated position of the X-ray microbeam could be determined from the intensity profile with high spatial resolution. By changing the sample position, diffraction patterns could be obtained from the laminated films across the PE/PP interfacial region. The thickness of the interfacial region of the annealed laminate was estimated as 5 μm judging from the changes of the diffraction intensities from the PE crystallites to the PP ones. The interfacial thickness depended on the thermal treatment of the film. It was found that the adhesion strength of the PE/PP laminate increased with increasing the interfacial thickness. Both of PE and PP chains entangled each other during laminate processing. The entangled molecular chains play important role as anchoring effect at the PE/PP interdiffusion region. However, the phase separation progressed with further crystallization by annealing. Thus, the adhesion strength of the PE/PP laminate was considered to be influenced by the interfacial thickness.     

Formation of aminosilane-oxide interphases

The aim of this work is to understand the interactions and interphase formation mechanisms between a liquid aminosilane oligomer (γ-APS) and glass, steel or gold surfaces as a function of the pH of the liquid aminosilane. When basic liquid γ-APS (pH 11.4) is applied onto a gold coated substrate, no interphase is detected. Similarly, when liquid γ-APS controlled at pH 8 is applied onto steel or glass substrates and cured, properties are the same as the bulk ones. In contrast, when the liquid γ-APS (pH 11.4) is applied onto steel or glass substrates and cured, an interphase, with chemical, physical and mechanical properties quite different from those of the bulk oligomer, is created between the substrate and the oligomer. Using various analytical techniques (DSC, FTIR, ICP, SEM, AFM, nano-indentation and XPS) it was shown that the amino-silane chemically reacts with and dissolves the oxide or hydroxide layers. Then metallic ions diffuse through the organic layer to form a complex, assumed to be of coordination type with the amine function of the oligomer molecule. These organometallic complexes are insoluble at room temperature and crystallize in the form of sharp needles. The Young's modulus of the resulting crystal is equal to approximately 5 GPa, i.e.over two orders of magnitude higher than that of the silane. In other words, these organometallic complexes act as a short fiber in a matrix.     

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

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

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

Improvement in damage tolerance of CFRP laminate using the hybridization method

Flexible epoxy resin was used as an interphase matrix to improve the transverse properties of carbon fiber reinforced plastic (CFRP) laminates. The use of flexible interphase is considered to act as the energy absorber and prevent the fiber/matrix interface cracking. The purposes of the present study are fabrication and characterization of CFRP laminates with flexible interphase. The effect of the flexible interphase on the damage tolerance of CFRP laminates was investigated. It was confirmed that transverse strength was improved and transverse crack progress was suppressed in the laminates with flexible interphase.     

Plasma-polymerized organosilicones as engineered interlayers in glass fiber/polyester composites

The plasma polymerization technique was used to surface modify glass fibers in order to form a strong but tough link between the glass fiber and the polyester matrix, and enable an efficient stress transfer from the polymer matrix to the fiber. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane in a mixture with oxygen gas were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physico-chemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Young's modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the pp-TVS/O₂ interlayer was 32% higher than that with industrial sizing developed for fiber-reinforced composites with a polyester matrix.     

Interphase phenomena in superconductive polymer-ceramic nanocomposites

Dynamic mechanical properties (elastic moduli, phase angle) for superconducting (SC) polymer–ceramic composites based on Y₁Ba₂Cu₃O_7?x SC oxide ceramic and superhighmolecular polyethylene have been investigated. The analysis of the obtained data shows a strong interaction of the polymeric binder with the surface of the ceramic grains. It is concluded that changes of packing and structure of the macromolecules occur at the ceramic–polymer interface. This is confirmed by melting enthalpy measurements of SC polymer–ceramic composites of different filler content. Scanning electron microscopy studies of the high temperature SC composites showed that the ceramic grains are evenly covered by the binder for both amorphous and crystalline polymers. EPR (electron paramagnetic resonance) spectra of polymer–ceramic composites have shown that the intensity of the EPR signals of Cu²⁺(1) depends on the nature and the content of binder. The Mn, Co, Zn, Ni containing superconducting composites have been obtained by frontal polymerization.     

Fiber bias in nanoindentation of polymer matrix composites

Nanoindentations were performed in the near fiber region of the matrix of a polymer matrix composite to attempt to determine the nanomechanical properties of the interphase. A possible fiber bias effect was observed and this effect was confirmed by performing nanoindentations in both the presence and in the absence of fiber. Changes in experimentation by using lower loads (40 μN and 80 μN) reduced the fiber bias effect. Cutting the samples at an angle to the fiber axis was performed to try to further reduce the fiber bias effect. The experimental variations considerably reduced the fiber bias effect. Specifically, the combination of angled cutting and use of reduced loads eliminated the fiber bias effect at distances greater than 150 nm from the fiber.