Abstract:The influence of solid-state drawing on the morphology of melt-spun poly(L-lactic acid) (PLLA) tapes, and the accompanying changes in mechanical and degradation behaviour have been studied. Mechanical properties are found to be strongly dependent on both applied draw ratio and drawing temperature. Moduli of these highly oriented tapes are significantly increased compared to as-extruded tapes at both ambient and elevated temperatures. Interestingly, drawing leads to a significant increase in elongation to break (~3 times) and toughness (~13 times) compared to as-extruded tapes. Structural and morphological characterization indicates strain-induced crystallization as well as an increase in orientation of the crystalline phase at small strains. Upon further stretching, an "overdrawing" regime is observed, with decreased crystalline orientation due to the breakage of existing crystals. For fixed draw ratios, a significant increase in Young's modulus and tensile strength is observed with increasing drawing temperature, due to a higher crystallinity and orientation obtained for tapes drawn at higher temperatures. FT-IR results indicate no crystal transformation after drawing, with the α-form being observed in all tapes. Hydrolytic degradability of PLLA was significantly reduced by solid-state drawing.

Since the discovery of graphene, various industries such as aerospace and automotive are trying to utilize this fascinating nanofiller to enhance components' performance. An important issue in the processing of nanoengineered composites is the interaction and potential filtration of nanofillers by the porous microfibre preform during liquid moulding processing. Here we demonstrate the filtration effect of graphene nanoplatelets (GNPs) during resin infusion of nanoengineered hierarchical composites, and for the first time we have successfully quantified this filtration effect by both electrical and optical methods. In addition, an alternative spraying method to deliver GNPs into composite laminates was also evaluated.

Smart heating devices with reliable self-regulating performances and high efficiency, combined with additional properties like mechanical flexibility, are of particular interest in healthcare, soft robotics, and smart buildings. Unfortunately, the development of smart heaters necessitates managing normally conflicting requirements such as good self-regulating capabilities and efficient Joule heating performances. Here, a simple and universal materials design strategy based on a series connection of different conductive polymer composites (CPC) is shown to provide unique control over the pyroresistive properties. Hooke's and Kirchhoff 's laws of electrical circuits can simply predict the overall pyroresistive behavior of devices connected in series and/ or parallel configurations, hence providing design guidelines. An efficient and mechanically flexible Joule heating device is hence designed and created. The heater is characterized by a zero temperature coefficient of resistance below the self-regulating temperature, immediately followed by a large and sharp positive temperature coefficient (PTC) behavior with a PTC intensity of around 10 6 . Flexibility and toughness is provided by the selected elastomeric thermoplastic polyurethane (TPU) matrix as well as the device design. The universality of the approach is demonstrated by using different polymer matrices and conductive fillers for which repeatable results are consistently obtained.the merits of plastics and conductive fillers. [1] Their capability of detecting and responding to external stimuli has offered a range of promising applications by performing both sensing (damage, [2] strain, [3] humidity, [4] vapor, [5] degradation, [6] and current-limiting), [7] and actuating (artificial muscles, [8] and electroactive shape memory) [9] functions. In particular, CPCs are practical choices for pyroresistive applications like self-regulating heaters, temperature sensors, and safe battery switches, due to their capability of changing electrical resistivity upon heating. [10] Since their introduction in the late 1970s, self-regulating heating devices have been widely adopted in applications like domestic heaters and deicing units. These smart heaters can operate at a nearly constant temperature over a broad range of voltage and dissipative conditions by utilizing the positive temperature coefficient (PTC) effect. The PTC effect, where the electrical resistivity increases with increasing operating temperature, is the main property that enables self-regulating heating. [11] The PTC phenomenon is generally explained by the mismatch of thermal expansion between the polymer matrix and the filler. [12] When the temperature increases and exceeds a certain threshold, the continuous network formed by the conductive fillers is disrupted. Due to expansion of the polymer matrix, the electrical conductivity and the current passing through the sample are reduced, regulating the temperature within a desired range. [13] Great efforts have been made to design PTC materials that p...

High performance transparent polymeric materials are of great interests in many fields including automotive and electronics. Conventional transparent plastics like polycarbonate (PC) and poly(methyl methacrylate) (PMMA) possess relatively unsatisfactory mechanical performance, while high performance polymeric systems like solid-state drawn high-density polyethylene (HDPE) typically have an opaque appearance, limiting applications where both mechanical and optical properties are required. In this study, we successfully combined high transparency and high strength in HDPE films by carefully controlling processing parameters

The fracture toughness of a noncontinuum fibrous network produced by electrospinning polyamide 6 nanofibers is investigated. The mechanical properties of the nanofiber network is observed to be independent of various incorporated macroscopic crack lengths, resulting in an apparent increase in fracture toughness with increasing crack length as evaluated using conventional fracture mechanics. Strain mapping of the nanofiber network indicates stress delocalization mechanisms operating around these macroscopic cracks in the network. The deformation behavior of the nanofiber network will therefore depend on the volume of fibers being loaded in the network and not the number of fibers in the cross-sectional width defining continuum sample mechanics. These results indicate a propensity for both the synthetic electrospun nanofibrous network in this work and potentially other nanofibrous networks to resist failure from macroscopic cracks incorporated within the material.

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The ionoSolv pretreatment generates a cellulose pulp by extracting hemicellulose and lignin using low-cost ionic liquids. In this study, cellulose pulp was obtained from Miscanthus × giganteus using the protic ionic liquid triethylammonium hydrogen sulfate [N2220][HSO4] with 20% water as a co-solvent and characterised in detail for its material properties as a function of pretreatment severity. We measured the particle size distribution, porosity and crystallinity of the unbleached pulps and the molar weight distribution of the cellulose contained within. We report that the surface area increased and the size of the pulp particles decreased as ionoSolv processing progressed. While the native cellulose I structure was maintained, the average degree of polymerisation of the cellulose was reduced to a DPn of around 300, showing the cellulose polymers are shortened. We correlate the pulp properties with enzymatic saccharification yields, concluding that enzymatic saccharification of the cellulose after ionoSolv pretreatment is mainly enhanced by removing hemicellulose and lignin. We also observed that overtreatment deteriorated saccharification yield and that this coincides with cellulose fibrils becoming coated with pseudolignin redeposited from the ionic liquid solution, as demonstrated by FT-IR spectroscopy. Pseudolignin deposition increases the apparent lignin content, which is likely to increase chemical demand in bleaching, suggesting that both glucose release and material use benefit from a minimum lignin content. Overall, this study demonstrates that cellulose pulps isolated with ionoSolv processing are not only a promising intermediate for high-yield release of purified glucose for biorefining, but also have attractive properties for materials applications that require cellulose I fibrils. Graphic abstract

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