Polymer International最新文献

This study developed a freshness indicator based on poly(vinyl alcohol) (PVA) and a biohybrid (BH) of Laponite® and anthocyanins adhered to linear low-density polyethylene (LLDPE) using cold atmospheric plasma (CAP). LLDPE was treated with CAP for 0 to 300 s, which resulted in an increased surface energy, characterized by an important increase in its polar component up to 120 s of treatment, due to the formation of polar groups on the surface of LLDPE. No changes in mechanical properties and water vapor permeability of LLDPE were observed. LLDPE–PVA–BH films were more homogeneous if BH was added before the acidification of the film-forming solution due to more negative zeta potential and lower particle size of BH in basic medium. Indicators made with BH were able to maintain color after 8 weeks of exposure to light, while those made with anthocyanin extract had fully degraded after 3 weeks. The freshness indicator's color changed from purple to blue and finally to green when exposed to ammonia hydroxide (30% NH₃) and from purple to blue when exposed to a simulant liquid of spoiled meat (0.03% NH₃). Similar color variance was observed when the indicator was applied to monitor shrimp freshness, changing from purple to blue when the shrimp pH reached pH 7.6. Thus, bilayer films of LLDPE–PVA and natural BH produced using CAP have potential food packaging applications. © 2024 Society of Chemical Industry.

A combination of experimental and simulation methods is adopted to study the relationship between micro-stress and micro-strain of a single spherulite upon uniaxial tensile deformation. To verify the simulation results and establish a suitable spherulite model, large-sized isotactic polypropylene spherulite is first cultured with isothermal crystallization, whose structural deformation upon application of uniaxial tension is recorded using a polarizing optical microscope. A nanoindenter is used to measure the elastic modulus of the spherulite and amorphous region, preparing the property parameters for numerical simulation. Modeling and meshing of the single spherulite are conducted with the finite element software ABAQUS. The entire deformation of the spherulite is analyzed with fixed strain as the boundary condition, and the microscopic stress and strain distribution inside and outside of the spherulite is obtained. The higher micro-stress region mainly locates at two poles in the equatorial direction, where might be the origin of craze. Generally, the simulation result is basically consistent with the experimental deformation process, which provides a new idea for the study of microscale structure and performance. © 2024 Society of Chemical Industry.

Soft sensors are flexible and stretchable, and because of this, they can be used on a wide range of surfaces, regardless of their size or shape. Such sensors may have applications such as in human–robot interaction, healthcare, soft robotics and human motion detection, where they can sense their surroundings and provide information. In this work, a soft piezoresistive sensor inspired by human finger ridges has been fabricated with liquid metal (EGaIn) electrode-filled embedded microchannels on elastomeric material (Ecoflex 0030) and characterized for a pressure range of 0 to 280 kPa at different compression rates. The sensitivity of the elastomeric sensor increases and the limit of detection (LOD) decreases with a reduction in compression rate. In this work, microchannels on soft and stretchable elastomers are cast on a metallic mold prepared using the micromilling method. This method reduces the complexity of developing microchannels on the soft material using the metallic mold. The sensor has microchannels with a cross-section of 200 μm × 200 μm, an active sensing area of 10 × 10 mm² and overall dimensions of 15 × 15 × 2 mm³. At a low compression rate, this sensor exhibits a maximum sensitivity of 0.126 kPa⁻¹ and a high linearity of 0.98, a LOD of 68 Pa, a response time of 30 ms and stability for 10 000 consecutive cycles at 100 kPa load. The developed sensor was shown to successfully differentiate various objects (soft to hard) based on the feedback it received when it was deployed on the gripper of an industrial manipulator. © 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Melanins are macromolecular pigments widely spread in many living organisms, with unique physical and chemical properties. Specifically, their conductive properties have drawn attention for applications in different devices; however, the electrochemical response is equally necessary for designing technologies in sustainable bioelectronics. In this sense, we report a comparative study of the redox electrochemical properties of non-functionalized and sulfonated melanins in different pH environments. The electrochemical response was investigated using cyclic voltammetry, electrochemical impedance spectroscopy, dielectric permittivity and AC/DC conductivity at pH 3, 5 and 7. The voltammetric currents were higher at low pH, in agreement with the known proton transport properties of melanins. The effect of pH on electrochemical properties was slightly more significant in non-functionalized pigments. Melanins with a higher 5,6-dihydroxyindole carboxylic acid/5,6-dihydroxyindole ratio showed high DC current and low impedance. No significant difference was observed in the dielectric relaxation process between the different samples. © 2024 Society of Chemical Industry.

Stretchable electrodes are essential parts for flexible electronics which are widely applied in human health monitoring, wearable electronics, robotics etc. Conductive elastomer composites are good candidates for stretchable electrodes; however, it is a challenge to maintain the resistance of conductive elastomer composites during elongation due to the departure of filler networks. In this work, highly stretchable and conductive polydimethylsiloxane (PDMS)/nickel-coated graphite (NCG) composites were fabricated based on the filler sedimentation method, in which NCG was modified by the coupling agent of the end alkyl group (dodecyltriethoxysilane, DTES) and end vinyl group (vinyltriethoxysilane, VTEO), considering the force between the filler networks and filler–matrix interface. The DTES modified NCG mainly improved the filler–matrix interface, which made the resistance of the composites clearly increase with strain, while the VTEO mainly heightened the NCG networks and made the resistance of the composites insensitive to a strain of 114% when the NCG content was 23.1 wt%. These quite interesting results are closely related to the force between the filler networks and filler–matrix interface during strain and they were proved in detail through the mechanical and electrical hysteresis performance. This work presents a facile method from the concept of stability of filler networks during strain to prepare highly stretchable and conductive composites. © 2024 Society of Chemical Industry.

Current ionic polymer–metal composite (IPMC) actuators have severe actuation drawbacks (i.e. low force output and poor stability), hampering their applications. To address these issues, poly(ethylene glycol)-grafted graphene oxide (PEG-GO) is synthesized and incorporated into a Nafion matrix, thus producing a PEG-GO hybrid Nafion film with better physiochemical properties for fabricating a high-performance, low-cost IPMC actuator. The modification of PEG to GO not only prevents GO agglomeration and sedimentation, but also avoids loss of PEG in water. Driven by a 0.2 Hz, 2.5 V electric field, the hybrid IPMC actuator exhibits superior electromechanical behaviors, i.e. a swing angle of 110.3°, a blocking force of 6.89 mN and a stable working time of 485 s, respectively increasing by 92%, 209% and 294% when compared to a pure Nafion actuator. © 2024 Society of Chemical Industry.

Modern society relies heavily on producing commercial and industrial plastics to improve the quality and quantity of our lives. However, increased fire risks threaten commercial operations and the potential impact of high-performance electronic and transportation technologies that utilize polymeric materials. Despite significant monitoring and reduction of commonly used halogenated flame retardants, their worldwide usage still poses environmental hazards. Many non-halogenated flame-retardant compounds are viable additives for synthetic polymers; however, their incorporation often results in reduced composite homogeneity and mechanical strength. This review focuses on reactive flame retardants and the effect of polymer structure on inherent flame retardance in recent studies. The synthesis and characterization of polymeric systems (e.g. polyurethanes, polyamides, polyimides, polyesters and epoxy resins) are discussed in terms of structure–flame-retardant performance using a complement of analytical tools, including thermogravimetric analysis, cone calorimetry, limiting oxygen index and UL 94 testing. These commercially important polymeric systems represent a broad compositional space for future adaptation and the discovery of increasingly modular polymeric materials with, while also contributing to the fundamental understanding of unique combinations of gas- and condensed-phase mechanisms of flame retardance. © 2024 Society of Chemical Industry.

Polyurea (PU) elastomers have attracted considerable attention in the field of protective polymeric coatings. In this work, a dithiol-terminated boronic ester was synthesized and used to incorporate dynamic boron–oxygen (B–O) bonds in the PU main chain based on thiol isocyanate while amino-terminated polydimethylsiloxane (PDMS) was introduced to retain good chain flexibility. The modified PU elastomer was found to have a microphase-separated structure in which the hard blocks served as physical crosslinks. The glass transition temperature (T_g) slightly increases when dynamic B–O bonds exist while further introduction of PDMS soft segment can lower T_g to −55.63 °C. The introduction of dynamic B–O bonds and diminished hydrogen bonding led to a decrease in mechanical strength and elongation at break. Interestingly, the simultaneous incorporation of PDMS and dynamic B–O bonds is favorable for strain rate dependence and suppressing stress relaxation. The potential for bond-exchange interactions between the dynamic B–O bonds and hydroxyl groups on metal surfaces substantially improved the adhesion of the PU elastomer to metal substrates. Therefore, our work can offer valuable insights for the structural design of functional PU coatings tailored for anti-impact applications. © 2024 Society of Chemical Industry.

The development of biobased and functionalized monomers along with eco-friendly photopolymerization processes represent promising methods for the development of renewable and more environmentally friendly thermosets. Thiol–ene ‘click’ photopolymerization is particularly advantageous in this regard; however, the materials derived from this method often exhibit low glass transition temperatures (T_g) and unsuitable thermomechanical properties for applications at room temperature. Herein, we report the synthesis of biobased allyl derivatives from quercetin, a renewable flavonoid compound widely available in fruits, vegetables and plants. We demonstrated the isolation of tetra- and penta-allylated quercetin (Q1 and Q2, respectively) and their subsequent photoactivated thiol–ene polymerization. By introducing a biobased thiol curing agent (PTTMP) derived from glycerol and mercaptopropionic acid, we produced fully biobased crosslinked thermosets with high content of aromatic moieties provided by the framework of the monomers. Real-time infrared spectroscopy showed the effective thiol–ene photopolymerization of Q1 and Q2 and PTTMP with conversions of 60% and 75%, respectively, after 15 min of UV irradiation. Due to the modulated crosslinking degree from the allyl group functionalization in the monomers, the biobased crosslinked networks showed storage moduli from 420 to 739 MPa, thermal stability from 220 to 257 °C and T_g values ranging from 75 to 90 °C. This work outlines straightforward strategies for creating biobased thermosets that overcome the limited thermomechanical properties of thiol–ene networks and offer potential antimicrobial and antioxidant properties. © 2024 Society of Chemical Industry.

Myocardial infarction is one of the main causes of death worldwide. After myocardial infarction, the damaged area is typically occupied with non-contractile scar tissue owing to the limited ability of cardiac cells to proliferate. Cardiac patches can potentially restore heart function by providing sufficient electrochemical properties to the damaged area and supporting the differentiation into and proliferation of cardiac cells. In this study, we developed for the first time a poly(mannitol sebacate) (PMS) based scaffold combined with 1% (w/w)multi-walled carbon nanotubes (MWCNTs) to produce a biocompatible cardiac patch by the solvent casting method. We characterized the resultant PMS-MWCNT scaffold in terms of chemical, physical, mechanical and electrical properties. The PMS/MWCNT patch revealed appropriate hydrophilicity, elasticity close to that of the target tissue, and electrical conductivity suited for a cardiac patch. The cytocompatibility of the composite was confirmed by the successful attachment and proliferation of human umbilical cord mesenchymal stem cells (HUC-MSCs). The PMS/MWCNTs further contributed to the differentiation of HUC-MSCs by significant overexpression of cardiac-specific proteins, i.e. troponin T and connexin 43, in the presence of 5-azacytidine. The findings of this study could be of assistance in the use and development of PMS-based composites as cardiac patches for myocardial tissue engineering applications. © 2024 Society of Chemical Industry.