a b s t r a c tNanocomposites consisting of thermoplastic polyurethaneeurea (TPU) and silica nanoparticles of various size and filler loadings were prepared by solution blending and extensively characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermal analysis, tensile tests, and nanoindentation. TPU copolymer was based on a cycloaliphatic diisocyanate and poly(tetramethylene oxide) (PTMO-2000) soft segments and had urea hard segment content of 20% by weight. TPU/silica nanocomposites using silica particles of different size (29, 74 and 215 nm) and at different loadings (1, 5, 10, 20 and 40 wt. %) were prepared and characterized. Solution blending using isopropyl alcohol resulted in even distribution of silica nanoparticles in the polyurethaneeurea matrix. FTIR spectroscopy indicated strong interactions between silica particles and polyether segments. Incorporation of silica nanoparticles of smaller size led to higher modulus and tensile strength of the nanocomposites, and elastomeric properties were retained. Increased filler content of up to about 20 wt. % resulted in materials with higher elastic moduli and tensile strength while the glass transition temperature remained the same. The fracture toughness increased relative to neat TPU regardless of the silica particle size. Improvements in tensile properties of the nanocomposites, particularly at intermediate silica loading levels and smaller particle size, are attributed to the interactions between the surface of silica nanoparticles and ether linkages of the polyether segments of the copolymers.

Green composites of poly(lactic acid) (PLA) and waste cellulose fibers (WCF) were produced by using a facile technique comprising high-shear mixing within relatively short processing times that facilitates the ease of processing of such materials and ensures the homogeneous dispersion of such fibers in thermoplastics due to shear rates as high as 5200 rpm. Key parameters, such as optimal concentrations, homogeneous dispersion, direct and indirect mechanical contributions of the fibers, interfacial interactions, and crystallinity of the PLA matrix, were examined for the sustainable production of PLA/WCF green composites with enhanced stiffness, strength, toughness, and impact resistance. Briefly, around one-fold, 50%, and 20% increase in the elastic modulus, tensile strength, and impact strength of PLA, respectively, were achieved by the addition of 30 wt % WCF. In addition, an 87% increase in the impact strength of PLA was also achieved by the incorporation of 5 wt % WCF.

Circumventing inherent embrittlement, poor heat resistance, and melt elasticity of poly­(lactic acid) (PLA) without compromising its remarkable stiffness and strength has become a particular challenge in polymer science due to increasing demand for green materials in emerging applications of sustainable chemistry and engineering. Achieving this without using any high-cost reagent/additive and/or complex processing technique is another critical aspect for developing industrially viable alternatives to petroleum-based commodity plastics. Here we demonstrate that high-shear mixing of PLA with waste cross-linked polyurethanes and waste cellulose fibers allows for overcoming its inherent embrittlement, poor heat resistance, and melt elasticity without compromising its superior stiffness and strength while suggesting a sustainable way of recycling/reusing industrial wastes as high added-value additives. We therefore achieve to produce stiff, strong, super-tough, and heat-resistant PLA-based green materials, for instance, with an elastic modulus of 4 GPa at 25 °C (∼30% higher than that of pure PLA), a storage modulus of 312 MPa at 90 °C (∼44 times higher than that of pure PLA), a tensile strength of 65 MPa (comparable to that of PLA), and an impact strength (toughness) of 52 kJ/m2 (∼2.3 times higher than that of pure PLA).

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This paper presents an experimental method to follow in-situ the chains network alteration of filled vulcanized rubbers induced by deformation. Macroscopic damage is first investigated on a series of EPDM by quantifying void fraction via Digital Image Correlation (DIC). In-situ DIC void fraction and the swollen pore fraction measured ex situ, i.e. on mechanically tested specimen, show analogous dependence on applied deformation. From such observation, Flory-Rehner equation is used by substituting fraction of swollen specimen by DIC void fraction to access to in-situ changes in network chains density, ν. Below the stretching ratio λ=3, reversible voids and accompanied by slight decrease of ν. Above λ=3, irreversible voids are associated with significant decrease of ν. Transition from reversible to irreversible voiding is finally ascribed to increased pore size of damaged elastically active chains network domains, as revealed by ex situ thermoporosimetry.