Coupling effect of molecular weight and crosslinking kinetics on the formation of rubber nanoparticles and their agglomerates in EPDM/PP TPVs during dynamic vulcanization

It is well-known that a fine dispersed rubber phase in thermoplastic vulcanizates (TPVs) is a key to obtain good mechanical properties and high elasticity of TPV products. Previous studies reported that the rubber nanodroplets formed during shearing blending can transform into rubber nanoparticles by in situ rapid crosslinking and these rubber nanoparticles spontaneously form agglomerates dispersed in a plastic matrix during dynamic vulcanization (DV). However, important influencing factors on the formation of rubber nanoparticles and their agglomeration during DV have not been reported yet. In this study, the coupling effect of the molecular weight (MW) of polypropylene (PP) and crosslinking kinetics including the crosslinking rate (CR) and crosslinking degree (CD) on the size of ethylene propylene diene monomer (EPDM) rubber nanoparticles and their agglomerates in EPDM/PP TPVs was systematically studied for the first time. The minimum diameter of EPDM nanodroplets was theoretically calculated by using the critical break-up law of viscoelastic melts for the blend with high MW PP or the critical capillary equation for the blend with low MW PP, and the real size of the EPDM nanoparticles was experimentally verified. Interestingly, the results show that the lower MW of the PP phase, lower CD and higher CR contribute to the formation of smaller rubber nanoparticles, whereas the higher MW of the PP phase and higher CD of the rubber phase contribute to the formation of smaller rubber nanoparticle agglomerates. This study provides guidance to optimize the microstructure of EPDM/PP TPVs for the preparation of high-performance TPV products.

Multidirectional Triple-Shape-Memory Polymer by Tunable Cross-linking and Crystallization

Medical fixing is one of the very important applications of the shape-memory polymer material, and the two important properties of the medical fixing material are that it perfectly fits the body during the fixing and easily detaches after being used. As the fixing and detachment are triggered by two independent stimuli in two opposite directions, it is necessary to develop multidirectional triple-shape-memory polymers. In this research, a series of polymer materials composed of trans-polyisoprene (TPI) and paraffin were prepared by melt blending and compression molding, and then the TPI was cross-linked by vulcanization. As a result of the large difference in the melting temperature and crystallization temperature between TPI and paraffin, the obtained polymer materials exhibit a triple-shape-memory behavior. According to the analysis of crystal behavior, microscopic morphology, and mechanical properties of the materials with different paraffin contents and TPI cross-linking density by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and dynamic mechanical thermal analysis, the shape-memory behavior of the obtained materials was tunable by the cross-linking density of TPI and the crystallization degree of TPI or paraffin. Compared with the traditional triple-shape-memory material, our samples are prepared in a more facile way and can recover at human body temperature (37 °C). Moreover, our TPI/paraffin material can realize more flexible multidirectional recovery, as well as can be reprogramed and used multiple times. To the best of our knowledge, there are few polymer materials reported, which can realize multidirectional recovery. These unique multidirectional and reprogramable properties will enable the application of this polymer material, especially in the medical fixing materials.

A silicone elastomer with optimized and tunable mechanical strength and self-healing ability based on strong and weak coordination bonds

A self-healable silicone elastomer is fabricated based on the synergistic effect of strong and weak coordination bonds.

Highly Stretchable Conductor by Self-Assembling and Mechanical Sintering of a 2D Liquid Metal on a 3D Polydopamine-Modified Polyurethane Sponge

A highly stretchable conductor was fabricated through dip-coating a new liquid metal (LM) electric ink on a polydopamine (PDA)-modified three-dimensional (3D) polyurethane sponge (PUS) followed by mechanical sintering. The LM was first sonicated to nanodroplets to reduce the consumption of LM and then modified by 3-mercaptopropionic acid (LMNPS-MPA) to improve the interfacial adhesion between LM and PUS. The denser and even distribution of LMNPS-MPA self-assembling on PDA-treated PUS (PUS-PDA) was successfully prepared via hydrogen bonding interactions. Mechanical sintering of 3D PUS-PDA coated by a two-dimensional (2D) LM layer was then conducted to obtain a continuous conductive network. Comparing with those of the reported 3D conductors, the resulting PUS-PDA-LM composite conductor shows both high electrical conductivity (478 S cm^-1) under a low LM consumption of 10 vol% and excellent conductivity stability with the relative resistance change, ΔR/R₀, of 2% at 50% strain under stretching deformation. The as-prepared PUS-PDA-LM composites were then successfully applied as flexible and stretchable light-emitting diode (LED) arrays with excellent conductivity and conductivity stability at different deformations. We believe that the 3D stretchable PUS-PDA-LM conductor has many potential applications in flexible sensors, flexible circuits, rollable displays, etc.

Photothermal-Induced Self-Healable and Reconfigurable Shape Memory Bio-Based Elastomer with Recyclable Ability

Photothermal-induced self-healable and shape memory materials have drawn much attention due to the rapidly growing technical applications and environmental requirements. As epoxy natural rubber (ENR) is a kind of bio-based elastomer with good mechanical properties, weather resistance, and air impermeability, it is of great significance to incorporate ENR with recyclable, photothermal-induced self-healable and shape memory properties. In this study, we report a simple method to cross-link ENR with dodecanedioic acids (DAs) through esterification reaction, and during the cross-linking process, a little aniline trimer (ACAT, a kind of oligoaniline) was added at the same time. Then, the ENR-DA-ACAT vitrimers that were covalently cross-linked with recyclable, self-healable, and multiple responsive properties were obtained, which also possessed various functions. As a result of the transesterification reactions at elevated temperatures, the ENR-based vitrimers possess the ability to be reprocessed and self-healed, and the mechanical properties could be maintained even after three consecutive breaking/mold pressing cycles. Besides, the vitrimer is also responsive to near-infrared (NIR) light and pH with the introduction of ACAT, and we also find that ACAT can be used as a catalyst to accelerate the transesterification reaction. Moreover, it is demonstrated that the ENR-DA-ACAT vitrimer could also be used to construct the reconfigurable shape memory polymer; the shape fixing ratio and shape recovery ratio are both above 95% in the reconfiguration process, and the multistage shape memory performance can also be achieved by NIR irradiation, which will potentially lead to a wide application for ENR in the field of actuators.

Simultaneously improved dielectric and mechanical properties of silicone elastomer by designing a dual crosslinking network

A homogenous silicone dielectric elastomer with simultaneously improved dielectric and mechanical properties is synthesized by designing a dual crosslinking network.

[Adenocarcinoma in a Meckel's diverticulum with multiple liver metastases and gastrointestinal hemorrhage: a case report]

Meckel's diverticulum is the most common congenital anomaly of the gastrointestinal tract, affecting approximately 2% of the population. It is a true diverticulum occurring on the anti-mesenteric border of the distalileum, typically within 100 cm of the ileo-caecal valve. Neoplasms arising in Meckel's diverticula are uncommon, and those reported in the literature are mainly carcinoid tumors, followed by gastrointestinal stromal tumors (GIST) and benign leiomyomas. Adenocarcinomas are extremely rare. Tumors in Meckel's present non-specifically with gastrointestinal complaints, such as bleeding, obstruction, inflammation or perforation. The suspicion of a Meckel's tumor is often not thought of at the initial. In this article we describe a 57-year-old woman who presented with massive rectal bleeding and severe anemia, later found to be caused by a adenocarcinoma arising from Meckel's diverticulum. The tumor was unfortunately highly aggressive. Multiple liver metastases had already existed when we discovered the primary mass. Later we performed a partial resection of the ileumto cease the bleeding. Meckel's diverticulum and the tumor were resected simultaneously. The pathological diagnosis confirmed adenocarcinoma arising from the Meckel's diverticulum. The final stage was pT4NxM1, stage IV according to the Union for International Cancer Control (UICC) classification. After operation we gave the patient first-line, mFOLFOX6 chemotherapy, but it turned out to be not effective. Rapid progress of the liver metastases and suspicion of multiple lung metastasis in short time after therapy indicated a bad outcome. We believe this is the first case of adenocarcinoma in a Meckel's diverticulum to be reported in domestic literature. The diagnosis of Meckel's tumor should be considered as inpatients'acute gastrointestinal complaints; when found incidentally at laparotomy, it should be carefully examined for any gross abnormality and resection should be considered.

Bioderived Rubber-Cellulose Nanocrystal Composites with Tunable Water-Responsive Adaptive Mechanical Behavior

Adaptive mechanical behaviors in nature have inspired the development of synthetic adaptive composites, with those responsive to water particularly relevant for biomedical applications. Polymer nanocomposites containing cellulose nanocrystals (CNCs) are prime examples of water-responsive mechanically adaptive materials. Although CNCs are biobased, the matrixes of these composites are exclusively petroleum-based synthetic elastomers, in sharp contrast to their biological counterparts. In this work, we attempted to probe the possibility of using bioderived rubber(s) as the matrix to fabricate CNC-nanocomposite with water-responsive adaptive mechanical behaviors. Specifically, natural rubber (NR) and epoxidized natural rubber (ENR) were used as the composite matrixes. Our results show that the water-responsive sensitivity and reversibility of ENR composites is much more drastic than that of NR composites. This is attributed to the strong CNC-polymer interaction (hydrogen bonding) for ENR, which leads to better filler dispersion and the formation of an extra CNC-polymer network in addition to the CNC-CNC filler network present in the NR composite. The synergistic effect of the dual networks plays a key role in tuning the mechanical properties and water-responsive sensitivity for various potential biomedical applications. Our study further provides guidance to make use of renewable resources to produce high value added water-responsive nanocomposites.

Unique microstructure of an oil resistant nitrile butadiene rubber/polypropylene dynamically vulcanized thermoplastic elastomer

This paper reports on the microstructure, morphological evolution and the properties of oil resistant nitrile butadiene rubber (NBR)/polypropylene (PP) thermoplastic vulcanizates (TPVs) prepared by dynamical vulcanization (DV).

Association of IL-18 polymorphisms with rheumatoid arthritis: a meta-analysis

Interleukin-18 (IL-18), an important proinflammatory cytokine, has been reported to play a potential pathological role in rheumatoid arthritis (RA). Results from previous studies on the association between IL-18 polymorphisms and RA are conflicting. To clarify this, an updated meta-analysis of all available studies on IL-18 polymorphisms and RA was conducted. Eligible articles were identified by searching databases, including PubMed, Ovid, Cochrane Library, EMBASE, and China Knowledge Resource Integrated Database, for the period up to May 1, 2015. The pooled odds ratios (ORs) with 95% confidence intervals (95%CIs) were used to assess the strength of association in the homozygote, heterozygote, dominant, recessive, and additive models. The software STATA (Version 13.0) was used for statistical analysis. Finally, 14 articles were included in the present meta-analysis. The IL-18 -607C/A polymorphism showed pooled ORs and 95%CIs for the homozygote model (AA vs CC: OR = 0.598; 95%CI = 0.395-0.907), and the association between the IL-18 -137G/C polymorphism and RA showed pooled ORs and 95%CIs for the homozygote (CC vs GG: OR = 0.699; 95%CI = 0.364-1.342) and heterozygote (CG vs GG: OR = 0.924; 95%CI = 0.803-1.064) models. In summary, the current meta-analysis, which was based on the most current studies, showed that the -607A/C, -920C/T, and -105A/C polymorphisms in IL-18 were significantly associated with increased RA risk. However, the -137C/G polymorphism was not associated with RA risk under any genetic model. More evidence is needed to support or deny such a conclusion.

Properties and unique morphological evolution of dynamically vulcanized bromo-isobutylene-isoprene rubber/polypropylene thermoplastic elastomer

We studied the microstructure, morphological evolution and the corresponding mechanism, and the properties of BIIR/PP TPV.

Largely improved electromechanical properties of thermoplastic dielectric elastomers by grafting carboxyl onto SBS through thiol–ene click chemistry

Modified SBS with largely improved electromechanical properties is prepared by grafting carboxyl groups onto the polybutadiene domains using a simple, effective and controllable photochemical thiol-ene click reaction.