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The melt–mixing of polylactide (PLA) with micro- and/or nanofillers is a key method used to obtain specific end-use characteristics and improvements of properties. So-called "insoluble" CaSO4 (CS) β-anhydrite II (AII) is a mineral filler recently considered for the industry of polymer composites. First, the study proves that AII made from natural gypsum by a specifically thermal treatment is highly stable compared to other CS forms. Then, PLAs of different isomer purity and molecular weights (for injection molding (IM) and extrusion), have been used to produce "green" composites filled with 20–40 wt.% AII. The composites show good thermal and mechanical properties, accounting for the excellent filler dispersion and stability. The stiffness of composites increases with the amount of filler, whereas their tensile strength is found to be dependent on PLA molecular weights. Interestingly, the impact resistance is improved by adding 20% AII into all investigated PLAs. Due to advanced kinetics of crystallization ascribed to the effects of AII and use of a PLA grade of high L-lactic acid isomer purity, the composites show after IM an impressive degree of crystallinity (DC), i.e., as high as 50%, while their Vicat softening temperature is remarkably increased to 160 °C, which are thermal properties of great interest for applications requiring elevated rigidity and heat resistance. [ABSTRACT FROM AUTHOR]

The objective of the study is the preparation and comprehensive characterization of novel high performance polylactide (PLA)-based composites designed with specific impact properties. Highly filled composites were obtained by melt-blending PLA and 40 wt % anhydrite II (AII) microfiller, the dehydrated form of calcium sulfate hemihydrate, a by-product having as origin the lactic acid (LA) fabrication process. The toughness of PLA-AII composites was improved by addition of a selected impact modifier (IM) based on ethylene-acrylate copolymer (Biomax® Strong 100, noted BS). PLA-AII composites containing (10 wt %) BS were prepared using two procedures: (1) the direct melt blending of all components in a single step and (2) the previously coating of AII by BS, followed by mixing of coated filler with PLA. These approaches were carried out to modify the phase structure and to determine their influence on the final composite properties. As reference samples, PLA and PLA-BS blends were accounted. The miscibility and phase morphology (differential scanning calorimetry and scanning electron microscopy), thermal stability (thermogravimetric analysis), and thermomechanical properties (DMTA, tensile, and impact tests) were investigated to explain the toughening mechanism in the BS-modified composites. Noticeable, an attractive threefold increase of impact strength with respect to the composite without modifier and remarkable thermomechanical performances were assessed. The composite obtained using BS-coated AII showed better properties (e.g., impact strength of 5.4 kJ/m2), improvements ascribed to the good filler dispersion and effective modification of interfacial regions (PLA-filler) by the BS-layer. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Reinforcing of polylactide (PLA) with fillers can be an interesting solution to reduce its global price and to improve specific properties. Starting from calcium sulfate (gypsum) as by-product of the lactic acid fermentation process, novel high performance composites have been produced by melt-blending PLA and this filler after a previous specific dehydration performed at 500°C for min. 1 h. Due to PLA sensitivity towards hydrolysis, it has first been demonstrated that formation of β-anhydrite II (AII) by adequate thermal treatment of calcium sulfate hemihydrate is a prerequisite. Then, the modification of filler interfacial properties with different coating agents such as stearic acid (SA) and stearate salts has been considered. The effect of surface treatment on molecular, thermal and mechanical properties has been examined together with the morphology of the resulting composites. To take advantage of the improved lubricity and better wetting characteristics, the filler was coated by up to 2% (by weight) SA. The coating of the filler leads to PLA–AII composites that surprisingly exhibit thermal stability, cold crystallization and enhanced impact properties. Such remarkable performances can be accounted for by the good filler dispersion as evidenced by SEM–BSE imaging of fractured surfaces. As far as tensile proprieties are concerned, notable utilization of uncoated filler or filler coated by stearate salts leads to PLA–AII composites characterized by higher tensile strength and Young's modulus values. The study represents a new approach in formulating new melt-processable grades with improved characteristic features by using PLA as polymer matrix. [ABSTRACT FROM AUTHOR]

In the category of biopolymers, polylactide or polylactic acid (PLA) is one of the most promising candidates considered for future developments, as it is not only biodegradable under industrial composting conditions, but it is produced from renewable natural resources. The modification of PLA through the addition of nanofillers is considered as a modern approach to improve its main characteristic features (mechanical, thermal, barrier, etc.) and to obtain specific end-use properties. Iron oxide nanoparticles (NPs) of low dimension (10–20 nm) such as magnetite (Fe3O4), exhibit strong magnetization in magnetic field, are biocompatible and show low toxicity, and can be considered in the production of polymer nanocomposites requiring superparamagnetic properties. Accordingly, PLA was mixed by melt-compounding with 4–16 wt.% magnetite NPs. Surface treatment of NPs with a reactive polymethylhydrogensiloxane (MHX) was investigated to render the nanofiller water repellent, less sensitive to moisture and to reduce the catalytic effects at high temperature of iron (from magnetite) on PLA macromolecular chains. The characterization of nanocomposites was focused on the differences of the rheology and morphology, modification, and improvements in the thermal properties using surface treated NPs, while the superparamagnetic behavior was confirmed by VSM (vibrating sample magnetometer) measurements. The PLA−magnetite nanocomposites had strong magnetization properties at low magnetic field (values close to 70% of Mmax at H = 0.2 T), while the maximum magnetic signal (Mmax) was mainly determined by the loading of the nanofiller, without any significant differences linked to the surface treatment of MNPs. These bionanocomposites showing superparamagnetic properties, close to zero magnetic remanence, and coercivity, can be further produced at a larger scale by melt-compounding and can be designed for special end-use applications, going from biomedical to technical areas. [ABSTRACT FROM AUTHOR]

Due to the added value conferred by zinc oxide (ZnO) nanofiller, e.g., UV protection, antibacterial action, gas-barrier properties, poly(lactic acid) (PLA)–ZnO nanocomposites show increased interest for utilization as films, textile fibers, and injection molding items. The study highlights the beneficial effects of premixing ZnO in PLA under given conditions and its use as masterbatch (MB), a very promising alternative manufacturing technique. This approach allows reducing the residence time at high processing temperature of the thermo-sensitive PLA matrix in contact of ZnO nanoparticles known for their aptitude to promote degradation effects onto the polyester chains. Various PLA–ZnO MBs containing high contents of silane-treated ZnO nanoparticles (up to 40 wt.% nanofiller specifically treated with triethoxycaprylylsilane) were produced by melt-compounding using twin-screw extruders. Subsequently, the selected MBs were melt blended with pristine PLA to produce nanocomposite films containing 1–3 wt.% ZnO. By comparison to the more traditional multi-step process, the MB approach allowed the production of nanocomposites (films) having improved processing and enhanced properties: PLA chains displaying higher molecular weights, improved thermal stability, fine nanofiller distribution, and thermo-mechanical characteristic features, while the UV protection was confirmed by UV-vis spectroscopy measurements. The MB alternative is viewed as a promising flexible technique able to open new perspectives to produce more competitive multifunctional PLA–ZnO nanocomposites. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the potential flame retardant effect of different metallic phytates as biosourced phosphorous additives for poly(lactic acid) (PLA). Starting from sodium phytate, the sodium cations were replaced by aluminum, iron or lanthanum cations as attested by elemental analysis. PLA-metallic phytate composites containing 20 or 30 wt% of additives were produced by melt blending in an internal mixer and their fire properties, thermogravimetric resistance have been characterized as well as the PLA chain degradation occurring during melt processing. The most significant flame retardant effect, observed by cone calorimeter test, was obtained when aluminum phytate was used. Cone calorimeter testing combined with pyrolysis combustion flow calorimetry (PCFC) analysis indicated that the barrier effect was more significant in the case of PLA filled with aluminum phytate. However, aluminum phytate proved to be responsible for PLA chain degradation during melt processing. Combinations of metallic phytate and native sodium phytate overcame this negative effect and allowed for limiting the thermal degradation of PLA during melt processing while preserving good fire performances, i.e. significant pHRR reduction and V-2 classification in UL-94 test. [ABSTRACT FROM AUTHOR]

Abstract: For the first time, an in-situ degradation monitoring system for biodegradable polymers is reported in present work. The proposed concept is based on a conductive biodegradable polymer composite, where carbon nanotubes (CNTs) are incorporated in poly(lactic acid) (PLA) in order to develop an intelligent biocomposite system that can sense biodegradation. Changes in electrical resistivity of the PLA/CNT nanocomposites were successfully correlated with degradation levels of the biopolymer. PLA/CNT nanocomposites demonstrated excellent degradation sensing abilities at CNT concentrations around the percolation threshold, with resistivity changes of about four orders of magnitude with biodegradation. In contrast to many other stimuli, biodegradation resulted in a reduction in resistivity due to an increased CNT network density after partial removal of the amorphous phase of the polymer matrix. [Copyright &y& Elsevier]

Highlights: [•] Nanocomposites of PLA and surface-treated ZnO rod-like nanoparticles. [•] Changes in PLA inherent permeation properties dependent on temperature and loading. [•] Good antibacterial activity against Gram-positive and Gram-negative bacteria. [•] The antibacterial performance was found to be time-dependent. [Copyright &y& Elsevier]

Abstract: Preparation of PLA based nanocomposites was carried out by using two different nanofillers: expanded graphite and organically modified montmorillonite. The addition and co-addition of these nanofillers to PLA using the melt-blending technique provides nanocomposites that showed significant enhancements in rigidity, thermal stability and fire retardancy of the polymer matrix. The presence of dispersed graphite nanolayers in PLA significantly accelerated the polyester crystallization, whereas the essential increase of thermal resistance is mainly connected to the addition of organoclay. The structure of the nanocomposites was examined by Wide Angle X-ray Scattering Analysis and Transmission Electron Microscopy. The improvement of thermal and mechanical properties obtained by the presence of both nanoparticles in PLA were associated to the good (co)dispersion and to the co-reinforcement effect, whilst the fire retardant properties were found to be related to the combined additive action of both nanofillers. [Copyright &y& Elsevier]

Abstract: Composites have been produced by melt-blending biodegradable polylactide (PLA) with commercially available expanded graphite (EG). Using different techniques of addition, the manifold effects of EG on PLA molecular, thermo-mechanical and fire-retardant properties were evaluated. The EG nanofiller provides PLA composites with competitive functional properties. They have a high rigidity, with Young''s modulus and storage modulus increasing with EG content. They also have excellent thermal stability while preserving the glass transition and melting temperature of the original PLA matrix. Purification and pre-dispersion of EG nanofiller proved beneficial for preserving PLA molecular weights and led to improved mechanical performance. The presence of dispersed graphene nanolayers in PLA significantly accelerated the polyester crystallization process. The flame retardant properties also displayed improvements with a large decrease in the maximum rate of heat release as recorded by cone calorimetry, whereas the horizontal burning test (UL94 HB) was successfully passed revealing non-dripping and char formation. [Copyright &y& Elsevier]

Abstract: Large amounts of stable β-anhydrite II (AII), a specific type of dehydrated gypsum and a by-product of lactic acid production process, can be melt-blended with bio-sourced and biodegradable polylactide (PLA) to produce economically interesting novel composites with high tensile strength and thermal stability. To enhance their toughness, while preserving an optimal stiffness, selected low molecular weight plasticizers (bis(2-ethylhexyl) adipate and glyceryl triacetate) and polymeric adipates with different molecular weights have been mixed with a specific PLA (l/d isomer ratio of 96/4) and 40wt% of AII using an internal kneader. Addition of up to 10wt% plasticizer into these highly filled compositions can trigger a fourfold increase of the impact strength with respect to the compositions without any modifier, cold crystallization properties and a significant decrease of their glass transition temperature. Moreover, these ternary compositions (PLA–AII–plasticizer) are clearly characterized by easier processing, notable thermo-mechanical performances and good filler dispersion. This study represents a new approach in formulating novel melt-processable polyester grades with improved characteristic features using PLA as biodegradable polymer matrix. [Copyright &y& Elsevier]

Abstract: Starting from calcium sulfate (gypsum) as a fermentation by-product of lactic acid fermentation, novel high performance composites have been produced by melt-blending polylactide (PLA) and previously dried calcium sulfate hemihydrate in a Brabender bench scale kneader at 190°C. Due to PLA sensitivity towards hydrolysis, it has first been demonstrated that formation of β-anhydrite II (AII) by adequate thermal treatment of calcium sulfate is a prerequisite. Then, the effect of filler content and mean diameter on thermal, mechanical and impact properties has been examined together with the morphology of the resulting materials. It shows that high tensile performances and impact strength are maintained up to a filler content of 20wt% without any increase of PLA crystallinity. Interestingly enough and provided that AII particles with a mean diameter of ca. 10μm were considered as PLA fillers, tensile and impact properties proved to be maintained at a very acceptable level at filler content as high as 50wt%. Such remarkable mechanical behavior can be accounted for by the excellent filler dispersion throughout the polyester matrix and much favorable interactions between CaSO4 particles and ester functions of PLA chains as evidenced by the use of predictive mathematical models for composite mechanical properties and SEM–BSE imaging of fractured surfaces. [Copyright &y& Elsevier]