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

MWNT Surface Self-Assembling in Fire Retardant Polyethylene-Carbon nanotubes nanocomposites

Multiwall carbon nanotubes (MWNT) were melt blended at different concentration with linear low density polyethylene (LLDPE). The nanotubes impart the fire-retardant characteristics to the polymer by formation of a thin protective film of MWNT/carbon char generated on the surface of the nanocomposites. The film formation mechanism is discusse

FDM Printability of PLA Based-Materials: The Key Role of the Rheological Behavior

Fused deposition modeling (FDM) is one of the most commonly used commercial technologies of materials extrusion-based additive manufacturing (AM), used for obtaining 3D-printed parts using thermoplastic polymers. Notwithstanding the great variety of applications for FDM-printed objects, the choice of materials suitable for processing using AM technology is still limited, likely due to the lack of rapid screening procedures allowing for an efficient selection of processable polymer-based formulations. In this work, the rheological behavior of several 3D-printable, commercially available poly(lactic acid)-based filaments was accurately characterized. In particular, each step of a typical FDM process was addressed, from the melt flowability through the printing nozzle, to the interlayer adhesion in the post-deposition stage, evaluating the ability of the considered materials to fulfill the criteria for successful 3D printing using FDM technology. Furthermore, the rheological features of the investigated materials were related to their composition and microstructure. Although an exhaustive and accurate evaluation of the 3D printability of thermoplastics must also consider their thermal behavior, the methodology proposed in this work aimed to offer a useful tool for designing thermoplastic-based formulations that are able to ensure an appropriate rheological performance in obtaining 3D-printed parts with the desired geometry and final properties

Identification of Plastics in Mixtures and Blends through Pyrolysis-Gas Chromatography/Mass Spectrometry

: In this paper, the possibility of detecting polymers in plastic mixtures and extruded blends has been investigated. Pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) allows researchers to identify multicomponent mixtures and low amounts of polymers without high spatial resolution, background noise and constituents mix interfering, as with molecular spectrometry techniques normally used for this purpose, such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy and differential scanning calorimetry (DSC). In total, 15 solid mixtures of low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyamide (PA) and polycarbonate (PC) in various combinations have been qualitatively analyzed after choosing their characteristic pyrolysis products and each polymer has been detected in every mix; thus, in extruded blends of high-density polyethylene (HDPE), PP and PS had varying weight percentages of the individual constituents ranging from 10 up to 90. Moreover, quantitative analysis of these polymers has been achieved in every blend with a trend that can be considered linear with coefficients of determination higher than 0.9, even though the limits of quantification are lower with respect to the ones reported in the literature, probably due to the extrusion process

Miscibility, rheological and thermo-mechanical properties of compatible biopolymer blends: influence of process parameters and natural surfactants

In the recent years, a growing interest in biodegradable plastics as an alternative to the conventional fossil fuel-based polymeric materials was developed. Particularly, PLA is broadly applicable for use as an alternative to petrochemical- derived products. In fact, this polymer is biodegradable and biocompatible and its properties are very similar to those of some synthetic fossil fuel-based polymers. Nevertheless, the range of application of PLA is limited due to its fragility, poor barrier properties and the limited temperature range at which it can be used. Various strategies were proposed to overcome these limitations, such as modifying the chemical structure of the polymer with plasticizers or blending with other polymers. In this work a polylactic acid PLA (70 wt%) and poly- hydroxy butyrate PHB (30 wt%) blend was prepared to obtain a bioplastic with mechanical properties intermediate between those of the two polymers. Specifically, the aims of the work were improve the miscibility of the blend and increase the thermo-mechanical properties. Two different approaches were used to achieve these goals: the study of the influence of process parameters and the introduction of natural compatibilizers in the blend. For the first, a co-rotating twin screw extruder LEISTRITZ ZSE 18/40D (Φ = 18 mm, L/D = 40) was used with three different screw profiles. The investigated formulations were: unfilled PLA/PHB blend and containing 5 wt% of an organo-modified clay (Cloisite 5). In the second part two types of natural surfactants with different chemical structure were used: an ethylene oxide/propylene oxide block copolymer (Synperonic) in the form of flakes and a mixture of two liquid surfactants with a variable lipophilic–hydrophilic index (HLB 12). In this case, PLA/PHB blends were prepared using a DSM Explore twin screw mini-extruder (T=180◦C and screw speed=100 RPM). The investigated formulations were: PLA/PHB with HLB12 ranging from 0.1 wt% to 5 wt% and PLA/PHB with Synperonic in the same range of content. Morphological, thermo-mechanical and rheological analyses were performed on each formulation in both case studies. Firstly, a correlation between the observed morphology and the screw profile was found; in particular, the milder screw profile was the best solution. This result is supported by rheological analyses: an increase of the storage modulus (G’) was obtained after the adding of Cloisite, while the unfilled PLA/PHB blend exhibits a shoulder in the G’ curve caused by the relaxation of the dispersed phase which is in form of droplets, showing the typical rheological response of an immiscible blend. In the second part of the study, the morphological and the rheological analyses showed that HLB 12 was more effective than Synperonic. In fact, the trend of G’ in this last formulation was similar to that of the uncompatibilized blend. Conversely, samples containing HLB 12 showed a different trend of G’ curve and a decrease of the curve slope in the terminal region can be observed, as well. This behaviour can be attributed to the obtainment of a complex morphology, significantly different from that of the neat blend PLA/PHB. Nevertheless, while for HLB 12 system, it was necessary the use of a solvent for their introduction into the extruder, the Synperonic presents the advantage of introducing a solid additive during the process. As far as the thermo-mechanical analyses are concerned, both types of compatibilizers induced excellent mechanical properties at high temperatures, resulting in an increased HDT value that allows to widen the application range of the obtained materials

Effect of the elongational flow on mechanical properties and thermal conductivity of polypropylene-boron nitride composite fibers

Polypropylene-based composites containing high loadings (up to 30 wt.%) of boron nitride (BN) were produced through melt compounding and then subjected to uniaxial elongational flow. The mechanical characterization of the obtained fibres indicated a progressive increase of their tensile properties with increasing the draw ratio. Furthermore, composites fibres exhibited enhanced thermal conductivity as compared to their isotropic counterparts. These results were ascribed to the effectiveness on the elongational flow in improving the filler dispersion; in fact, SEM observations pointed out the achievement of a more homogeneous morphology for the composites fibers, with the disappearance of BN agglomerates observed in the isotropic materials and some preferential orientation of the embedded fillers along the flow direction

PLA-PHB polymer blends: study on processing conditions and influence of compatibilizers

In the recent years, the concerns related to the environmental issues stimulated an increasing interest towards the application of biodegradable polymers. However, the use of these renewable resources, in alternative to the conventional petrochemical derived products, has some disadvantages such as limited thermo-mechanical properties. A possible and effective method to overcome some biopolymers limitations is the development of bio-based polymer blends