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The structure and properties of blends of a novel polyethylene terephthalate copolymer (COPET) obtained by chemical recycling of commercial PET with high-molar-mass poly-L-lactide (PLLA) are investigated and compared to corresponding composites with chopped flax fibres. The focus is on the morphology at nano- and micro-scales, on the thermal characteristics and on the mechanical behaviour. The blends are immiscible, as evidenced by virtually unchanged glass transition temperatures of the blend components compared to the neat polymers (49 °C for COPET and 63 °C for PLLA by DSC). At low PLLA content, the blends display a sea–island morphology with sub-micron to micron droplet sizes. As the composition approaches 50/50, the morphology transitions to a coarser co-continuous elongated structure. The blends and composites show strongly improved stiffness compared to COPET above its glass transition temperature, e.g., from melt behaviour at 60 °C for COPET alone to almost 600 MPa for the 50/50 blend and 500 MPa for the 20% flax composite of the 80/20 COPET/PLLA blend. The flax fibres increase the crystallisation rate of PLLA in blends with dispersed PLLA morphology. The evidence of cavitation on the fracture surfaces of blends shows that despite the immiscibility of the components, the interfacial adhesion between the phases is excellent. This is attributed to the presence of aliphatic ester spacers in COPET. The tensile strength of the 80/20 blend is around 50 MPa with a Young’s modulus of 2250 MPa. The corresponding 20% flax composite has similar tensile strength but a high Young’s modulus equal to 6400 MPa, which results from the individual dispersion and strong adhesion of the flax fibres and leads close to the maximum possible reinforcement of the composite, as demonstrated by tensile tests and nano-indentation. The Ashby approach to eco-selection relying on the embodied energy (EE) further clarifies the eco-friendliness of the blends and their composites, which are even better positioned than PLLA in a stiffness versus EE chart.

A major societal issue of disposal and environmental pollution is raised by the enormous and fast-growing production of single-use polyethylene terephthalate (PET) bottles, especially in developing countries. To contribute to the problem solution, an original route to recycle PET in the form of value-added environmentally friendly thermoplastic composites with banana fibres (Musa acuminata) has been developed at the laboratory scale. Banana fibres are a so far undervalued by-product of banana crops with great potential as polymer reinforcement. The melt-processing constraints of commercial PET, including used bottles, being incompatible with the thermal stability limits use of natural fibres; PET has been modified with bio-sourced reactants to produce co-polymers with moderate processing temperatures below 200 °C. First, commercial PET were partially glycolyzed with 1.3-propanediol to produce co-oligomers of about 20 repeating units, which were next chain extended with succinic anhydride and post-treated in a very unusual “soft solid state” process at temperatures in the vicinity of the melting point to generate co-polymers with excellent ductility. The molar mass build-up reaction is dominated by esterification of the chain ends and benefits from the addition of succinic anhydride to rebalance the acid-to-hydroxyl end-group ratio. Infra-red spectroscopy and intrinsic viscosity were extensively used to quantify the concentration of chain ends and the average molar mass of the co-polymers at all stages of the process. The best co-polymers are crystallisable, though at slow kinetics, with a Tg of 48 °C and a melting point strongly dependent upon thermal history. The composites show high stiffness (4.8 GPa at 20% fibres), consistent with the excellent dispersion of the fibres and a very high interfacial cohesion. The strong adhesion can be tentatively explained by covalent bonding involving unreacted succinic anhydride in excess during solid stating. A first approach to quantify the sustainable benefits of this PET recycling route, based on a rational eco-selection method, gives promising results since the composites come close to low-end wood materials in terms of the stiffness/embodied energy balance. Moreover, this approach can easily be extended to many other natural fibres. The present study is limited to a proof of concept at the laboratory scale but is encouraging enough to warrant a follow-up study toward scale-up and application development.

Poly l-Lactide (PLLA) composites with short flax fibers (from 0 to 10 wt/wt%)with close to maximum theoretical stiffness are prepared by melt-compounding and injection-molding followed by a two-step isothermal crystallization protocol that fully separates the nucleation and growth stages (Tammann). The use of fast chip scanning calorimetry for thermal characterization avoids the complicating issues of crystal reorganization during the cooling and heating steps between the isothermal stages. Flax fibers are very efficient and selective nucleating agents of PLLA favoring the ordered 𝜶 form. The resulting morphology exhibits trans-crystallization on the fibers surface, predominantly at fiber defects, with a clear reduction of crystal size and a very strong fiber matrix cohesion. Efficient nucleation further leads to a large reduction of the overall crystallization time. Avrami analysis evidences a reduction of crystal growth dimensionality, consistent with both optical and scanning electron microscopy. The high modulus of the composites is unambiguously related to the strong orientation of the fibers in the tensile direction, to their high aspect ratio and to the excellent matrix-fibers cohesion. On the other hand, the tensile strength and hardness appear isotropic within experimental uncertainty and are unfavorably influenced by the presence of the fibers and by the two-stage annealing.

The specific influence of polyethersulfone (PES) endfunctionalization with chlorine or hydroxyl end groups at same molar mass on PES-epoxy composites based on a high-performance tetra-epoxide with di-amine hardener resin (RTM6) is investigated in terms of morphology,thermal behavior, and toughness. A model study on PES filaments embedded in epoxy precursor is first performed to compare the interdiffusion and resulting morphology upon curing. PES-OH shows a larger interdiffusion distance compared to PES-Cl in the model systems and the laminates. This effect is more pronounced at high heating rate. Cross sections and fracture surfaces of composite panels are analyzed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) spectroscopy to establish the link between the microstructures and fracture mechanisms. The toughness of PES-OH-modified epoxy composites is doubled compared to unmodified reference panels, whereas the PES-Cl shows no improvement. The favorable influence of PES-OH is ascribed to enhanced miscibility, interfacial adhesion and morphology, resulting from the better affinity between hydroxyl-terminated PES and the epoxy-resin.

The interdiffusion between a low and a high viscosity epoxy resin was studied on model systems representing the novel composite manufacturing process called “Same Qualified-Resin Transfer Molding” (SQ-RTM). Neat resin model systems were first characterized after curing by Raman spectroscopy, energy dispersive X-ray microscopy, and nano-indentation, all methods reveal an interdiffusion distance of about 700–900 µm. Transmission electron microscopy further revealed a complex morphological gradient structure in the interdiffusion zone. The interdiffusion distance was about 800 µm in the absence of carbon fibers, reducing down to 500 µm when the viscous resin was replaced by the corresponding prepreg, due to the geometrical constraints imposed by the fibers. Moreover, some asymmetry was observed in the interdiffusion profile because of the viscosity difference between the resins. The results obtained on the model systems were found to match very well the interdiffusion profiles generated in real SQ-RTM composites processed with the same combination of resins. POLYM. ENG. SCI. 56:1061–1069, 2016. © 2016 Society of Plastics Engineers

The electrokinetic properties of hollow fiber polymer membranes were investigated from tangential streaming current/streaming potential and electric conductance measurements. The experiments were conducted with a number of fibers n between 1 and 10 and for three fiber lengths l . The quite good linearity of (i) streaming current/potential data versus pressure difference and (ii) streaming current coefficient and “ SP × G ” ( SP : streaming potential coefficient; G : cell electric conductance) data versus n / l shows that expressions of the streaming current and streaming potential derived in laminar flow are also valid for turbulent flux conditions (provided the electrical double layer lies within the laminar sublayer near the surface). The high experimental conductance, the nonlinear dependence of electric conductance on the number of fibers and the variation of streaming potential coefficient with n and l suggest that the solution in which fibers are immersed makes contribution to the cell electric conductance. A non negligible part of the total streaming current is likely to flow through the macroporous body of fibers. Unlike flat membranes, the contributions of the skin surface and the porous body of the fibers to the streaming current cannot be separated for this type of material due to the impossibility of varying channel cross section. The conversion of tangential electrokinetic measurements into zeta-potential of lumen surface is then no more possible. In such cases, it is advisable to carry out streaming current measurements (or to combine streaming potential measurements with electric conductance measurements) because the streaming current (or the product SP × G ) is not affected by the cell electric conductance and can then be considered a property of membrane surface.