Crystallization kinetics of poly(lactic acid)-talc composites

The crystallization kinetics of Poly(lactic acid) / talc composites were determined over a range of 0 wt.% to 15 wt.% of talc. Talc was found to change the crystallization kinetics. The presence of talc increases the crystallization rate and this increase is related to talc concentration and to crystallization temperature. In order to understand the effect of talc and PLA crystallinity on mechanical properties, dynamic mechanical thermal analyses were performed on Poly(lactic acid) / talc composites before and after an annealing process. It was demonstrated that the presence of crystals improves thermo-mechanical properties but in order to achieve good results at high temperatures the reinforcing effect of a filler such as talc is necessar

PLA/PA bio-blends: induced morphology by extrusion

The effect of processing conditions on the final morphology of Poly(Lactic Acid) (PLA) with bio-based Polyamide 10.10 (PA) 70/30 blends is analyzed in this paper. Two types of PLA were used: Commercial (neat PLA) and a rheologically modified PLA (PLAREx), with higher melt elasticity produced by reactive extrusion. To evaluate the ability of in situ micro-fibrillation (µf) of PA phase during blend compounding by twin-screw extrusion, two processing parameters were varied: (i) Screw speed rotation (rpm); and (ii) take-up velocity, to induce a hot stretching with different Draw Ratios (DR). The potential ability of PA-µf in both bio-blends was evaluated by the viscosity (p) and elasticity (k’) ratios determined from the rheological tests of pristine polymers. When PLAREx was used, the requirements for PA-µf was fulfilled in the shear rate range observed at the extrusion die. Scanning electron microscopy (SEM) observations revealed that, unlike neat PLA, PLAREx promoted PA-µf without hot stretching and the aspect ratio increased as DR increased. For neat PLA-based blends, PA-µf was promoted during the hot stretching stage. DMTA analysis revealed that the use of PLAREx PLAREx resulted in a better mechanical performance in the rubbery region (T > Tg PLA-phase) due to the PA-µf morphology obtained.Peer ReviewedPostprint (published version

Chopped basalt fibres: A new perspective in reinforcing poly(lactic acid) to produce injection moulded engineering composites from renewable and natural resources

This paper focuses on the reinforcing of Poly(lactic acid) with chopped basalt fibres by using silane treated and untreated basalt fibres. Composite materials with 5–10–15–20–30–40 wt% basalt fibre contents were prepared from silane sized basalt fibres using extrusion, and injection moulding, while composites with 5–10–15 wt% basalt fibre contents were also prepared by using untreated basalt fibres as control. The properties of the injection moulded composites were extensively examined by using quasi-static (tensile, three-point bending) and dynamic mechanical tests (notched and unnotched Charpy impact tests), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), heat deflection temperature (HDT) analysis, dimensional stability test, as well as melt flow index (MFI) analysis and scanning electron microscopic (SEM) observations. It was found that silane treated chopped basalt fibres are much more effective in reinforcing Poly(lactic acid) than natural fibres; although basalt fibres are not biodegradable but they are still considered as natural (can be found in nature in the form of volcanic rocks) and biologically inert. It is demonstrated in this paper that by using basalt fibre reinforcement, a renewable and natural resource based composite can be produced by injection moulding with excellent mechanical properties suitable even for engineering applications. Finally it was shown that by using adequate drying of the materials, composites with higher mechanical properties can be achieved compared to literature data

Effect of the viscosity ratio on the PLA/PA10.10 bioblends morphology and mechanical properties

PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10-50wt.% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt.% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt.% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bio-blends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt.% and co-continuity was observed already at 44 wt.% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications.Peer ReviewedPostprint (published version

Twin-screw extrusion impact on natural fibre morphology and material properties in poly(lactic acid) based biocomposites

Natural fibres from miscanthus and bamboo were added to poly(lactic acid) by twin-screw extrusion. The influence of extruder screw speed and of total feeding rate was studied first on fibre morphology and then on mechanical and thermal properties of injected biocomposites. Increasing the screw speed from 100 to 300 rpm such as increasing the feeding rate in the same time up to 40 kg/h helped to preserve fibre length. Indeed, if shear rate was increased with higher screw speeds, residence time in the extruder and blend viscosity were reduced. However, such conditions doubled electrical energy spent by produced matter weight without significant effect on material properties. The comparison of four bamboo grades with various fibre sizes enlightened that fibre breakages were more consequent when longer fibres were added in the extruder. Longer fibres were beneficial for material mechanical properties by increasing flexural strength, while short fibres restrained material deformation under heat by promoting crystallinity and hindering more chain mobility

Influence of Print Orientation on Surface Roughness in Fused Deposition Modeling (FDM) Processes

In the present paper, we address the influence of print orientation angle on surface roughnessobtained in lateral walls in fused deposition modelling (FDM) processes. A geometrical model isdefined that considers the shape of the filaments after deposition, in order to define a theoreticalroughness profile, for a certain print orientation angle. Different angles were considered between 5¿and 85¿. Simulated arithmetical mean height of the roughness profile, Ra values, were calculated fromthe simulated profiles. The Ra simulated results were compared to the experimental results, whichwere carried out with cylindrical PLA (polylactic acid) samples. The simulated Ra values were similarto the experimental values, except for high angles above 80¿, where experimental roughness decreasedwhile simulated roughness was still high. Low print orientation angles show regular profiles withrounded peaks and sharp values. At a print orientation angle of 85¿, the shape of the profile changeswith respect to lower angles, showing a gap between adjacent peaks. At 90¿, both simulated andexperimental roughness values would be close to zero, because the measurement direction is parallelto the layer orientation. Other roughness parameters were also measured: maximum height ofprofile, Rz, kurtosis, Rku, skewness, Rsk, and mean width of the profile elements, Rsm. At high printorientation angles, Rz decreases, Rku shifts to positive, Rsk slightly increases, and Rsk decreases,showing the change in the shape of the roughness profiles.Postprint (published version

Influence of citric acid and water on thermoplastic wheat flour/poly(lactic acid) blends. I: Thermal, mechanical and morphological properties

Wheat flour was plasticized with glycerol and compounded with poly(lactic acid) in a one-step twin-screw extrusion process in the presence of citric acid with or without extra water. The influence of these additives on process parameters and thermal, mechanical and morphological properties of injected samples from the prepared blends, was then studied. Citric acid acted as a compatibilizer by promoting depolymerization of both starch and PLA. For an extrusion without extra water, the amount of citric acid (2 parts for 75 parts of flour, 25 parts of PLA and 15 parts of glycerol) has to be limited to avoid mechanical properties degradation. Water, added during the extrusion, improved the whole process, minimizing PLA depolymerization, favoring starch plasticization by citric acid and thus improving phases repartition