Morphologies, Compatibilization and Properties of Immiscible PLA-Based Blends with Engineering Polymers: An Overview of Recent Works.

Poly(L-Lactide) (PLA), a fully biobased aliphatic polyester, has attracted significant attention in the last decade due to its exceptional set of properties, such as high tensile modulus/strength, biocompatibility, (bio)degradability in various media, easy recyclability and good melt-state processability by the conventional processes of the plastic/textile industry. Blending PLA with other polymers represents one of the most cost-effective and efficient approaches to develop a next-generation of PLA-based materials with superior properties. In particular, intensive research has been carried out on PLA-based blends with engineering polymers such as polycarbonate (PC), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and various polyamides (PA). This overview, consequently, aims to gather recent works over the last 10 years on these immiscible PLA-based blends processed by melt extrusion, such as twin screw compounding. Furthermore, for a better scientific understanding of various ultimate properties, processing by internal mixers has also been ventured. A specific emphasis on blend morphologies, compatibilization strategies and final (thermo)mechanical properties (tensile/impact strength, ductility and heat deflection temperature) for potential durable and high-performance applications, such as electronic parts (3C parts, electronic cases) to replace PC/ABS blends, has been made.

Unraveling Ammonia and Trimethylamine Uptake on Conductive Doped Polyaniline.

Polyaniline (PAni)-based sensors are a promising solution for ammonia (NH3) detection at the ppb level. However, the nature of the NH3-PAni interaction and underlying drivers remain unclear. This paper proposes to characterize the interaction between doped PAni (dPAni) sensing material and NH3 by using a Knudsen cell. First, to characterize the dPAni interface, the probe-gas method, i.e., titration of surface sites with a gas of specific properties, is deployed. The dPAni interface is found to be homogeneous with more than 96% of surface sites of acid nature or with hydroxyl functional groups. This result highlights that basic gases such as amines might act as interfering gases for NH3 detection by polyaniline-based sensors. Second, the adsorption isotherms of NH3 and trimethylamine (TMA) on dPAni are reported at ambient temperature conditions, 293 K. The uptake of NH3 and TMA on dPAni follows a Langmuir-type behavior. This approach allows for the first time to quantify the uptake of NH3 and TMA on gas-sensor materials and determine typical Langmuir adsorption parameters, i.e., the partitioning coefficient, KLang, and the maximum surface coverage, Nmax. The corresponding values obtained for NH3 and TMA are Klang (NH3) = 19.7 × 10-15 cm3 molecules-1 Nmax (NH3) = 11.6 × 1014 molecules cm-2, KLang (TMA) = 7.0 × 10-15 cm3 molecules-1 Nmax (TMA) = 5.0 × 1014 molecules cm-2. KLang and Nmax values of NH3 are higher than those of TMA, suggesting that NH3 is more efficiently taken up than TMA on dPAni. The results of this work suggest that strong hydrogen bonding drives the performance of a polyaniline-based gas sensor for NH3 and amines. In conclusion, the Knudsen cell approach allows reconsidering the fundamentals of NH3 interactions with dPAni and provides new insights on drivers to enhance sensing properties.

Rheological Considerations in Processing Self-Reinforced Thermoplastic Polymer Nanocomposites: A Review.

The present review relates to the field of nanocomposite materials comprising a thermoplastic nanofibrillar phase dispersed in a matrix that is also thermoplastic. The fact of forming the nanofibrillar phase in situ during melt processing gives it the role of a reinforcing nanofiller for thermoplastic materials. This paper discusses the major factors influencing the formation of self-reinforced nanofibrillar polymer composite (NFC) materials throughout manufacturing steps. More specifically, the rheological considerations allowing the prediction of the in situ nanofibrillation during melt blending and post-processing as well as the methods of production of these polymer nanocomposites are described. The major challenges related to the future development in the field of NFCs are addressed. The concept of self-reinforced nanofibrillar polymer materials shows great potential in lightweight eco-design processes and represents a new approach to polymer nanocomposite recycling for a variety of industrial applications.

Solvent-Free Design of Biobased Non-isocyanate Polyurethanes with Ferroelectric Properties.

Increasing energy autonomy and lowering dependence on lithium-based batteries are more and more appealing to meet our current and future needs of energy-demanding applications such as data acquisition, storage, and communication. In this respect, energy harvesting solutions from ambient sources represent a relevant solution by unravelling these challenges and giving access to an unlimited source of portable/renewable energy. Despite more than five decades of intensive study, most of these energy harvesting solutions are exclusively designed from ferroelectric ceramics such as Pb(Zr,Ti)O3 and/or ferroelectric polymers such as polyvinylidene fluoride and its related copolymers, but the large implementation of these piezoelectric materials into these technologies is environmentally problematic, related with elevated toxicity and poor recyclability. In this work, we reveal that fully biobased non-isocyanate polyurethane-based materials could afford a sustainable platform to produce piezoelectric materials of high interest. Interestingly, these non-isocyanate polyurethanes (NIPUs) with ferroelectric properties could be successfully synthesized using a solvent-free reactive extrusion process on the basis of an aminolysis reaction between resorcinol bis-carbonate and different diamine extension agents. Structure-property relationships were established, indicating that the ferroelectric behavior of these NIPUs depends on the nanophase separation inside these materials. These promising results indicate a significant potential for fulfilling the requirements of basic connected sensors equipped with low-power communication technologies.

Processing of PVDF-based electroactive/ferroelectric films: importance of PMMA and cooling rate from the melt state on the crystallization of PVDF beta-crystals.

Poly(vinylidene difluoride) (PVDF) displays attractive ferroelectric/piezoelectric properties and its polar ß-crystals are specifically targeted for achieving electroactive applications. However, their direct crystallization from the melt state represents a challenging task that has never been addressed using melt-state processes. The use of poly(methyl methacrylate) (PMMA) is herein investigated to promote the PVDF polar ß-phase using melt-blending and extrusion-calendering technologies. The presence of the ß-phase is here confirmed by ATR-FTIR and WAXS experiments with blends at a PMMA content as low as 5 wt%. The key role of PMMA for the ß-phase crystallization from the melt state was unambiguously highlighted with the help of Flash DSC experiments in non-isothermal cooling mode from the melt state. PMMA is able to efficiently shift the α-to-ß crystal transition to lower cooling rates (>100-200 °C s-1), making the achievement of the PVDF polar ß-phase for these blends compatible with conventional processing tools. A crystal phase diagram is proposed for the PVDF/PMMA blends to highlight the dual effects of both PMMA and cooling rate on the PVDF crystallization during melt-processing. Ferroelectric properties were even observed for the blends containing PMMA up to 10 wt% with the highest remanent polarization obtained at 5 wt% PMMA. After 10 wt% PMMA, a progressive transition from ferroelectric to pseudo-linear dielectric behavior is observed more likely due to the presence of PMMA in the interlamellar amorphous phase of the polar PVDF spherulites as shown by SAXS experiments. In this work, we successfully demonstrated that PMMA plays a key role in the crystallization of PVDF polar crystals from the melt state, enabling large-scale and continuous extrusion processing of PVDF-based materials with attractive dielectric properties for sensing and harvesting applications.

Polylactide/Poly(ω-hydroxytetradecanoic acid) Reactive Blending: A Green Renewable Approach to Improving Polylactide Properties.

A green manufacturing technique, reactive extrusion (REx), was employed to improve the mechanical properties of polylactide (PLA). To achieve this goal, a fully biosourced PLA based polymer blend was conceived by incorporating small quantities of poly(ω-hydroxytetradecanoic acid) (PC14). PLA/PC14 blends were compatibilized by transesterification reactions promoted by 200 ppm titanium tetrabutoxide (Ti(OBu)4) during REx. REx for 15 min at 150 rpm and 200 °C resulted in enhanced blend mechanical properties while minimizing losses in PLA molecular weight. SEM analysis of the resulting compatibilized phase-separated blends showed good adhesion between dispersed PC14 phases within the continuous PLA phase. Direct evidence for in situ synthesis of PLA-b-PC14 copolymers was obtained by HMBC and HSQC NMR experiments. The size of the dispersed phase was tuned by the screw speed to "tailor" the blend morphology. In the presence of 200 ppm Ti(OBu)4, inclusion of only 5% PC14 increased the elongation at break of PLA from 3 to 140% with only a slight decrease in the tensile modulus (3200 to 2900 MPa). Furthermore, PLA's impact strength was increased by 2.4× that of neat PLA for 20% PC14 blends prepared by REx. Blends of PLA and PC14 are expected to expand the potential uses of PLA-based materials.

Stereocomplexation of polylactide enhanced by poly(methyl methacrylate): improved processability and thermomechanical properties of stereocomplexable polylactide-based materials.

Stereocomplexable polylactides (PLAs) with improved processability and thermomechanical properties have been prepared by one-step melt blending of high-molecular-weight poly(l-lactide) (PLLA), poly(d-lactide) (PDLA), and poly(methyl methacrylate) (PMMA). Crystallization of PLA stereocomplexes occurred during cooling from the melt, and, surprisingly, PMMA enhanced the amount of stereocomplex formation, especially with the addition of 30-40 % PMMA. The prepared ternary blends were found to be miscible, and such miscibility is likely a key factor to the role of PMMA in enhancing stereocomplexation. In addition, the incorporation of PMMA during compounding substantially raised the melt viscosity at 230 °C. Therefore, to some extent, the use of PMMA could also overcome processing difficulties associated with low viscosities of stereocomplexable PLA-based materials. Semicrystalline miscible blends with good transparency were recovered after injection molding, and in a first approach, the thermomechanical properties could be tuned by the PMMA content. Superior storage modulus and thermal resistance to deformation were thereby found for semicrystalline ternary blends compared to binary PLLA/PMMA blends. The amount of PLA stereocomplexes could be significantly increased with an additional thermal treatment, without compromising transparency. This could result in a remarkable thermal resistance to deformation at much higher temperatures than with conventional PLA. Consequently, stereocomplex crystallization into miscible PLLA/PDLA/PMMA blends represents a relevant approach to developing transparent, heat-resistant, and partly biobased polymers using conventional injection-molding processes.