Micro- and nano-mechanical characterization of polyamide 11 and its composites containing cellulose nanofibers

Nanocomposites from polyamide 11 and dried cellulose nanofibers (CNs), 16–30 nm in thickness and 50–400 nm in length, were prepared via direct melt mixing and their micro- and nano-mechanical properties were studied. (PF) QNM (Quantitative Nanomechanical Mapping) method was used to map nanomechanical properties at the surface of polyamide 11 and nanocomposites. This new AFM method emphasized both the increased modulus in nanocomposites as compared to the matrix and the microstructure on different levels in polyamide 11 and its nanocomposites. PF QNM showed that their crystalline structure consists of bundles of lamellar stacks, 200–350 nm in width and 20–40 nm wide lamellar stacks. Moreover, PF QNM study emphasized higher structural order in nanocomposites with 3 and 5 wt.% CNs and lower in the nanocomposite with 8 wt.% CNs as compared to the reference. These observations were verified and are consistent with both crystallinity values determined by DSC and micro-mechanical test results. The oriented bundles of lamellar stacks, observed by PF QNM, could be considered as the main blocks determining high mechanical properties for the studied nanomaterials.     

Dielectric properties and thermal stability of γ-irradiated inorganic nanofiller modified PVC

The dielectric characteristics of polyvinyl chloride nanocomposites containing titania, silica and alumina at the concentration of 5% were investigated by dielectric spectroscopy. The sharp modification in the permittivity and dielectric loss of neat and irradiated PVC samples over the low frequency range may be explained by the interaction between external electrical field and the dipoles formed during high energy exposure. The material characterization is completed by the thermal stability assay based on the accumulation of carbonyl units in the sample matrices, which provides the differences in the molecular level contact between host polymer and fillers.     

Hybrid polymeric latexes containing magnetite

The work describes a study for preparing polystyrene (PSt) and polymethyl methacrylate (PMMA) latex, containing magnetite (Fe₃O₄), covalently bounded to the polymeric chains. The magnetite was functionalized with various alkoxysilanes containing double bonds: vinyltriethoxysilane (VTES), methacryloyl propyl trimethoxysilane (MPTS) and vinyldimethylethoxysilane (VMe₂TES). The ferrite-silane composite forms higher average size particles with MPTS than with VTES. Ferrite functionalized with VMe₂TES forms stable latexes with both PSt and PMMA polymers. PSt forms also stable latexes with ferrite functionalized with VTES but unstable with ferrite functionalized with MPTS.     

Nucleation and crystal growth in sheared granular sphere packings

We investigate the nucleation of ordered phases, their symmetries, and distributions in dense frictional hard sphere packings as a function of particle volume fraction ?, by imposing cyclic shear and constant applied pressure conditions. We show, with internal imaging, that the nucleating crystallites in the bulk consist of 10-60 spheres with hexagonal close packed (hcp) order and nonspherical shape, that are oriented preferentially along the shear axis. Above ?=0.62±0.005, crystallites with face centered cubic (fcc) order are observed with increasing probability, and ordered domains grow rapidly. A polycrystalline phase with domains of fcc and hcp order is observed after hundreds of thousands of shear cycles.     

Poly(lactic acid)/Poly(3-hydroxybutyrate) Biocomposites with Differently Treated Cellulose Fibers

The growing concern about environmental pollution has generated an increased demand for biobased and biodegradable materials intended particularly for the packaging sector. Thus, this study focuses on the effect of two different cellulosic reinforcements and plasticized poly(3-hydroxybutyrate) (PHB) on the properties of poly(lactic acid) (PLA). The cellulose fibers containing lignin (CFw) were isolated from wood waste by mechanical treatment, while the ones without lignin (CF) were obtained from pure cellulose by acid hydrolysis. The biocomposites were prepared by means of a melt compounding-masterbatch technique for the better dispersion of additives. The effect of the presence or absence of lignin and of the size of the cellulosic fibers on the properties of PLA and PLA/PHB was emphasized by using in situ X-ray diffraction, polarized optical microscopy, atomic force microscopy, and mechanical and thermal analyses. An improvement of the mechanical properties of PLA and PLA/PHB was achieved in the presence of CF fibers due to their smaller size, while CFw fibers promoted an increased thermal stability of PLA/PHB, owing to the presence of lignin. The overall thermal and mechanical results show the great potential of using cheap cellulose fibers from wood waste to obtain PLA/PHB-based materials for packaging applications as an alternative to using fossil based materials. In addition, in situ X-ray diffraction analysis over a large temperature range has proven to be a useful technique to better understand changes in the crystal structure of complex biomaterials.     

Recycled polypropylene with improved thermal stability and melt processability

Journal of Thermal Analysis and Calorimetry - Polypropylene (PP) is a versatile polymer, with a wide range of applications, from household appliances to packaging and automotive components....     

Thermal and mechanical behavior of biodegradable polyester films containing cellulose nanofibers

Journal of Thermal Analysis and Calorimetry - Agricultural waste is a valuable source of advanced materials. Cheap nanocellulose may be obtained from plum shells agricultural residues and further...     

Morphology and thermal stability of bacterial cellulose/collagen composites

The aim of this paper was to prepare composites of bacterial cellulose (BC) and collagen to evaluate both the effect of collagen on the morphological, mechanical and thermal properties of BC and the effect of BC on the thermal stability of collagen for designing composites with increased potential biomedical applications. Two series of composites were prepared, the first series by immersing BC pellicle in solutions of collagen obtained in three forms, collagen gel (CG), collagen solution (CS) and hydrolysed collagen (HC), followed by freeze drying; and the second series of composites by mixing BC powder in solutions of collagen (CG, CS and HC), also followed by freeze drying. The properties of obtained composites were evaluated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), mechanical tests, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results revealed that BC acts as a thermal stabilizer for CS matrix, while with CG matrix it interacts synergistically leading to composites with improved properties. On the other hand, the BC sheet impregnated with collagen has a significantly improved thermal stability. Collagen (as HC, CS or CG) has also a positive influence on the mechanical properties of lyophilized BC sheet. A four times increase of modulus was observed in BC/HC and BC/CG composites. and an increase of 60 times for BC/CS. The spectacular increase of elastic modulus and tensile strength in the case of BC/CS composite was explained by the easier penetration of collagen solution in the BC network and impregnation of BC fibrils as revealed by SEM and AFM analyzes.

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