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Abstract: Bio‐based polyamide 11 (PA11)–graphene nanoplatelets (GNP) nanocomposites with different filler concentrations were prepared by melt extrusion using a masterbatch dilution process. Graphene platelets are uniformly distributed into the polymer matrix as revealed by scanning electron microscopy. The incorporation of graphene significantly improves the electrical conductivity and dielectric constant of PA11. GNPs favors the matrix crystallization; crystallization temperature and degree of crystallinity of the nanocomposites tend to increase with increase in graphene loading. Tensile properties (strength and modulus) are slightly improved by the incorporation of GNP into the PA11 matrix (up to +25% and +56%, respectively, for 5 wt% GNPs) at the expense of ductility (elongation at break divided by 5 for 5 wt% GNPs). [ABSTRACT FROM AUTHOR]

This article aims to investigate the flexural creep behaviour as a function of temperature of long glass fibre polyamide 6.6 taking into account the thermal-oxidative degradation occurring during the test. The mould geometry has been chosen so as to reproduce some geometrical accidents (e.g. sharp frontal and tangential steps) occurring on industrial moulds. The nominal fibre content (10, 40 and 55 wt%), initial fibre length (short glass fibre, long glass fibre), load rate (up to 70%) and creep temperature (23℃, 100℃ and 130℃) have been considered to estimate the Findley’s model coefficients. A first investigation on the polyamide 6.6 degradation under thermo-oxidative environment has been led to understand the mechanisms of thermal-degradation of the polyamide 6.6 composites. The pure polyamide 6.6 matrix has shown a 20% increase of flexural modulus during the first period of ageing attributed to a combined chain scissions and cross-linking reactions. Then, a decrease of properties attributed to predominant chain scission mechanism was noticed after 1000 h of thermal exposure reaching up to 30% after 5000 h. In case of reinforced polyamide 6.6, the flexural properties tend to increase (+6.5%) up to 2000 h of exposure. The least square method has then permitted to evaluate the material coefficients from the experimental data; the instantaneous creep strain has been estimated from a power law representation. In any cases, the calculations are in a good accordance with experimental measurements. [ABSTRACT FROM AUTHOR]

The energy-harvesting efficiency of melt processed polyamide 11 (PA11) films and its nanocomposites have been investigated as a function of filler type and content. In the present work, nanoclays have been used as structural modifiers in a PA11 matrix. The nanocomposites were prepared using layered clays, Cloisite 20A, 10A, and Na+, by extrusion process through varying the filler content, 1, 2, 4, and 5 wt.%. The crystalline structure of these nanocomposites has been studied by X-ray diffractometer. It has been demonstrated that layered silicates are not significant for the structural quality of the obtained nanocomposites. Regarding the interlayer peak of different clays, it has also been revealed that Cloisite 20A is partially exfoliated, whereas 10A and Na+are totally exfoliated in the PA11 matrix. From mechanical and dynamic mechanical analyses, it was found that the addition of layered silicates results in an increase in mechanical properties. The piezoelectric strain coefficientd33and dielectric constantεRhave been measured on polarized films at ambient temperature. Among all the prepared nanocomposites only Cloisite Na+-loaded PA11 nanocomposites showed the best piezoelectric constant. This observation showed that piezoelectric constant not only depends on the crystalline phases but also on the nature of the filler. Cloisite Na+is more polar than other modified clays and high polarity leads to a better polarization response. A specific method for the quantification of energy vibration recovery has been developed for these nanocomposites. The capabilities of vibrational energy recovery were studied on PA11 loaded with Cloisite Na+. [ABSTRACT FROM AUTHOR]

This paper focuses on the development and the validation of flexural modulus and flexural strength predictive models of long glass fibre reinforced polyamide 6.6 (PA66). Based on previous injection moulding optimization of 40 wt% long glass fibre PA66, a microstructure analysis was investigated on glass fibre reinforced PA66 by varying the parameters of the material (fibre length, fibre content, fibre diameter). In a first phase, analytical models established within the framework of the processing condition limits previously determined have been elaborated. These models lead to a good experimental/calculation correlation but remain limited to a mould and part design. In a second phase the flexural modulus and maximal flexural stress have been then estimated from structural models based on a five layer morphological description of the composites (local residual fibre length, local fibre content and fibre orientations). The long glass fibre PA66 composites were characterized in terms of fibre content distribution model and fibre orientation model through the part thickness. The experimental/model correlation was achieved whatever the process variability is (mould, material and processing conditions) both for the flexural modulus or flexural strength. The models have been then validated with an industrial part. Finally, a correlation between the two studied properties has been revealed depending on the nature of the composite matrix (PA66, PA6 or PP). [ABSTRACT FROM AUTHOR]

This paper aims at improving the mechanical behavior of biobased brittle amorphous polylactide (PLA) by extrusion melt-blending with biobased semi-crystalline polyamide 11 (PA11) and addition of halloysite nanotubes (HNT). The morphological analysis of the PLA/PA11/HNT blends shows a strong interface between the two polymeric phases due to hydrogen bonding, and the migration of HNTs towards PA11 phase inducing their selective localization in one of the polymeric phases of the blend. A 'salami-like' structure is formed revealing a HNTs-rich tubular-like (fibrillar) PA11 phase. Moreover, HNTs localized in the dispersed phase act as nucleating agents for PA11. Compared to neat PLA, this leads to a remarkable improvement in tensile and impact properties (elongation at break is multiplied by a factor 43, impact strength by 2, whereas tensile strength and stiffness are almost unchanged). The toughening mechanism is discussed based on the combined effect of resistance to crack propagation and nanotubes load bearing capacity due to the existence of the fibrillar structure. Thus, blending brittle PLA with PA11 and HNT nanotubes results in tailor-made PLA-based compounds with enhanced ductility without sacrificing stiffness and strength. [ABSTRACT FROM AUTHOR]

This work aims at numerically simulating the flow of nanocomposites in a twin-screw mixer so as to develop a prediction tool of nanofiller dispersion and distribution in a polymer matrix during processing. The rheological behaviour of polyamide 6 / carbon nanotubes blends (PA6/MWCNT) containing from 1 to 5 wt.% of MWCNT was investigated over a large range of shear rates (0.1 to 100 s-1) and temperatures (230 to 245 °C). The macroscopic dispersion of the nanotubes was assessed by dynamic rheometry. Viscosity laws of the nanocomposites were characterized and implemented in a finite element software package to compute the velocity, pressure and temperature fields during the mixing process. A good agreement was founded between the calculated and measured torques. The dispersive and distributive capability of the flow was numerically evaluated and compared to the nanotubes dispersion quality experimentally qualified by oscillatory rheometry. Experimental and numerical results are complementary and allow better understanding the mixing capability of the twin-screw mixer used to compound nanocomposites. [ABSTRACT FROM AUTHOR]

Examines the evolution of structure in films of polyamide-6 drawn on Cellier tenter frame laboratory tester under conditions of simultaneous equibiaxial stretching and planar uniaxial stretching. Utilization of the tilted film method to obtain trichroic spectra; Observations on the molecular orientation of crystalline structure; Combination of infrared trichroism with the analysis of the structural factor spectra.

Abstract: The uniaxial drawing of PA6/tie/PE multilayer blown films is investigated in relation to the behavior of the pure components. The tensile stress–strain behavior of the multilayers obeys a simple additive mixture law of the one of the components which is consistent with the parallel mechanical coupling of the layer structure of the films. No significant difference is observed in the crystallographic evolution of each layer in the multilayer films as compared with the parent monolayer films. The rupture of the multilayer films yet appears to be directly governed by the PA6 layer, as it triggers an early rupture of the PE layer without decohesion. This contrasts with the rupture behavior upon biaxial drawing that was previously shown to strongly depend on the layer thickness ratio: the thicker the PE layer, the higher the strain at break of both the PE and the PA6 layers. Besides, the strain at break of the PA6 layer in the multilayers under biaxial drawing was greater than that of neat PA6. However, a common feature to uniaxial and biaxial drawing is the similar β–α strain-induced phase transformation and the same limiting value of the α-crystal content at rupture in the PA6 layer, for all multilayer films and the PA6 monolayer film as well. This finding supports the previously proposed rupture criterion based on flaw propagation through the crack-prone α-crystalline phase when this latter phase reaches a critical content for mechanical percolation. The major differences and similarities between the two drawing modes are discussed in consideration of the different state of stress that modifies the pathway of the β–α phase transformation. [Copyright &y& Elsevier]

Abstract: Polyamide 6 (PA 6)/halloysite nanotubes (HNT) nanocomposites were prepared by melt-extrusion compounding via masterbatch dilution process. A homogeneous dispersion of HNTs in PA 6 matrix was achieved. Differential scanning calorimetric measurements showed that addition of HNTs into PA 6 matrix enhanced the crystallization temperature and degree of crystallinity, thus indicating an effective nucleation induced by the addition of HNTs. Upon halloysite addition, glass transition temperature, storage modulus, Young modulus, tensile strength and notched Charpy impact strength increased without loss of ductility. For the first time, the essential work of fracture (EWF) concept was used to analyse the toughening and fracture behaviour of PA 6/HNT systems. Significant increase (+38%) of the essential work of fracture of PA 6/HNT nanocomposites was noticed at HNTs contents as low as 4wt.%. [Copyright &y& Elsevier]

Abstract: Polyamide 6 (PA6)/clay nanocomposites, based on organo-modified and pristine (i.e. purified but non-modified) montmorillonite, were prepared using a water-assisted extrusion process based on the injection of water during extrusion. The formation of a single PA6/water phase during extrusion (shown by High Pressure Differential Scanning Calorimetry (HPDSC)) improves the clay dispersion, decreases the PA6 melting temperature by 66°C (so-called cryoscopic effect), and thus prevents the polymer matrix degradation during processing. This process enables the compounding of pristine clay-based nanocomposites whose dispersion state, thermal and mechanical performances are close to what is generally reported for organo-modified montmorillonite-based nanocomposites. Advantage was taken of water-assisted extrusion to optimize the clay dispersion by increasing shear rate and of the cryoscopic effect to limit the degradation by decreasing the processing temperature. Using these conditions PA6/pristine clay nanocomposites properties are similar to those of more conventional PA6/organomodified clay nanocomposites. [Copyright &y& Elsevier]