Comparative investigation of fillers loading effect on morphological, micromechanical, and thermal properties of polyvinyl alcohol/biofillers-based composites.

Polyvinyl alcohol (PVA)-based biocomposites were fabricated by the incorporation of chitosan (Ch), cellulose fibers (CS), and their mixture (1:1 ratio). Fillers with various loading (2, 4, 8, and 10 wt.-%) were incorporated into PVA employing the solution casting method. The fillers and biocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), brightfield microscopy, tensile and microindentation tests, contact angle measurement and thermogravimetric analysis (TGA). FTIR spectra revealed the removal of lignin, and intermolecular H-bonding between PVA and fillers promoting their filler-matrix interfacial interactions. Crystallographic results showed varied crystallite sizes and crystallinity of composites. Microscopic techniques revealed a uniform filler distribution, attributed to their compatibility with PVA. Tensile and microindentation tests demonstrated a decreased tensile strength (3.3-8.2 MPa of the composites compared to 15.7 MPa of the matrix) and Martens hardness (HM) of biocomposites. However, their value was increased with higher filler concentration, signifying the mechanical reinforcement. Contact angle analysis confirms the decreased wettability (hydrophilicity) of biocomposites, attributed to higher compatibility of fillers with PVA and intermolecular H-bonding between them. A slightly decreased thermal stability of biocomposites with filler incorporation is implied by TGA results despite their uniform distribution and strong matrix-filler interfacial interactions.

Fracture Toughness, Radiation Hardness, and Processibility of Polymers for Superconducting Magnets.

High fracture toughness at cryogenic temperature and radiation hardness can be conflicting requirements for the resins for the impregnation of superconducting magnet coils. The fracture toughness of different epoxy-resin systems at room temperature (RT) and at 77 K was measured, and their toughness was compared with that determined for a polyurethane, polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Among the epoxy resins tested in this study, the MY750 system has the highest 77 K fracture toughness of KIC = 4.6 MPa√m, which is comparable to the KIC of PMMA, which also exhibits linear elastic behaviour and unstable crack propagation. The polyurethane system tested has a much higher 77 K toughness than the epoxy resins, approaching the toughness of PC, which is known as one of the toughest polymer materials. CTD101K is the least performing in terms of fracture toughness. Despite this, it is used for the impregnation of large Nb3Sn coils for its good processing capabilities and relatively high radiation resistance. In this study, the fracture toughness of CTD101K was improved by adding the polyglycol flexibiliser Araldite DY040 as a fourth component. The different epoxy-resin systems were exposed to proton and gamma doses up to 38 MGy, and it was found that adding the DY040 flexibiliser to the CTD101K system did not significantly change the irradiation-induced ageing behaviour. The viscosity evolution of the uncured resin mix is not significantly changed when adding the DY040 flexibiliser, and at the processing temperature of 60 °C, the viscosity remains below 200 cP for more than 24 h. Therefore, the new resin referred to as POLAB Mix is now used for the impregnation of superconducting magnet coils.

A New Way of Toughening of Thermoset by Dual-Cured Thermoplastic/Thermosetting Blend.

The work aims at establishing the optimum conditions for dual thermal and electron beam curing of thermosetting systems modified by styrene/butadiene (SB)-based triblock copolymers in order to develop transparent and toughened materials. The work also investigates the effects of curing procedures on the ultimate phase morphology and mechanical properties of these thermoset⁻SB copolymer blends. It was found that at least 46 mol% of the epoxidation degree of the SB copolymer was needed to enable the miscibility of the modified block copolymer into the epoxy resin. Hence, an electron beam curing dose of ~50 kGy was needed to ensure the formation of micro- and nanostructured transparent blends. The micro- and nanophase-separated thermosets obtained were analyzed by optical as well as scanning and transmission electron microscopy. The mechanical properties of the blends were enhanced as shown by their impact strengths, indentation, hardness, and fracture toughness analyses, whereby the toughness values were found to mainly depend on the dose. Thus, we have developed a new route for designing dual-cured toughened micro- and nanostructured transparent epoxy thermosets with enhanced fracture toughness.