Volume 40, Issue 7

In this study, silicone rubber foam (SF) was prepared through cross-linking and foaming. The effects of ethanol content on the SF were investigated in terms of the physical properties, static cushioning properties, dynamic thermomechanical properties, and dynamic fatigue properties. The cell structure was characterized using scanning electron microscopy and its relationship with the SF properties was analyzed. With increasing ethanol content, the cell diameter increases gradually and its uniformity deteriorates. Moreover, the density, tensile strength, and elongation at breaking of the SF samples gradually decrease. In addition, with the increase of strain and stress, the cushioning coefficient of SF decreases initially and then increases, and the fatigue times worsens with increasing ethanol content. However, fatigue process has little effect on the cushioning performance of SF, which means the SF can be used as reusable packaging materials and thereby reduce environmental pollution.

In this research, three modified chitosan-based hydrogels are synthesized, i.e., a crosslinked chitosan hydrogel and semi- and fully-interpenetrating polymer network (IPN) chitosan hydrogels fabricated using poly(N-vinyl-pyrrolidone). A non-modified chitosan hydrogel was also synthesized as a control. These samples were compared regarding their swelling behavior and mechanical properties. The hydrogels were characterized by Fourier Transform Infrared (FTIR) analysis and microscopy observations. The effect of crosslinking on the swelling capacity and on the swelling kinetics were evaluated in distilled water, simulated gastric fluid (SGF), and simulated intestinal fluid (SIF) at 37 °C, and the data were interpreted using various kinetic models. Finally, the mechanical properties were evaluated based on the tensile strength using a universal tensile testing machine. The results revealed that the swelling process conformed to the Schott model (pseudo-second-order kinetics), with Fickian diffusion as the diffusion mechanism type. The hydrogels all showed similar trends in their swelling kinetics. However, the full-IPN hydrogel exhibited the lowest equilibrium swelling capacity and the highest swelling rate. The mechanical test results indicate that the crosslinking model affects the resulting tensile strength.

The bead foaming behavior of ether- and an ester-based Tensor Processing Unit (TPU) resins were investigated in a lab-scale reactor using supercritical CO 2 as the blowing agent. The samples were saturated at various saturation temperatures and the effects of hard segment crystallization during the saturation on the foaming behavior of the TPU samples were explored. The results revealed that the different HS crystallization tendencies and possible CO 2 solubility differences in two TPU grades led to their different foaming behaviors. The ester-based TPU could be foamed within a wider saturation temperature range and revealed an easier cell growth and foam expansion while the ether-based TPU showed a more limited cell growth behavior and hence processing window. The effect of pre-annealing and hence the isothermally induced HS crystallization on the foaming behavior of the ether-based TPU and the influence of depressurization rate on the foaming behavior of ester-based TPU was also explored.

Polymer dispersed liquid crystalline (PDLC) membrane with intrinsic thermal conductivity was prepared by dispersing liquid crystalline polysiloxane containing crosslinked structure (liquid crystalline polysiloxane elastomer (LCPE)) into polyvinyl alcohol (PVA). Chemical structures were characterized by Fourier transform infrared (FT-IR) and 1 H-NMR, and microscopic structures were analyzed by polarizing optical microscope (POM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The thermal conductivity of PDLC membrane was characterized by hot disk thermal constants analyzer, and the tensile properties were measured by tensile testing machine. Thermal properties were characterized by differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA). The results show that LCPE was dispersed in PVA uniformly, and the mesogenic monomer of LCPE formed microscopic ordered structures in PDLC membrane. Meanwhile, hydrogen-bond interaction was formed between LCPE and PVA chain. Both microscopic-ordered structure and the hydrogen-bond interaction improved the phonon transmission path, and the thermal conductivity of PDLC membrane was up to 0.74 W/m⋅K, which was 6 times higher than that of pure PVA film. PDLC membrane possessed proper tensile strength and elongation at break, respectively 5.18 MPa and 338%. As a result, PDLC membrane can be used as thermal conductive membrane in electronic packaging and other related fields.

The recent technology of geopolymer concrete is a substitute material for ordinary portland cement concrete which is produced from the polycondensation reaction of aluminosilicate materials with alkaline activator solutions. The cost of river sand is high since the demand for the same is also high. Manufactured sand is used as a replacement material for river sand in geopolymer concrete. This paper mainly focuses to find the properties of fly ash (FA) – based geopolymer concrete under ambient cured temperature like compressive strength, stress strain behaviour, modulus of elasticity, Poission’s ratio and impact resistance. The result of geopolymer concrete is compared with ordinary portland cement concrete. The elasticity modulus and Poission’s ratio of geopolymer concrete are lower than conventional concrete. The Stress-strain behaviour of geopolymer concrete is similar to conventional concrete. The impact resistance of geopolymer concrete is very good when compared with conventional concrete.

The citrate-based thermoset elastomer is a promising candidate for bone scaffold material, but the harsh curing condition made it difficult to fabricate porous structure. Recently, poly (1, 8-octanediol-co-Pluronic F127 citrate) (POFC) porous scaffold was creatively fabricated by chitin nanofibrils (ChiNFs) supported emulsion-freeze-casting. Thanks to the supporting role of ChiNFs, the lamellar pore structure formed by directional freeze-drying was maintained during the subsequent thermocuring. Herein, bioactive glass (BG) was introduced into the POFC porous scaffolds to improve bioactivity. It was found the complete replacement of ChiNF particles with BG particles could not form a stable porous structure; however, existing at least 15 wt% ChiNF could ensure the formation of lamellar pore, and the interlamellar distance increased with BG ratios. Thus, the BG granules did not contribute to the formation of pore structure like ChiNFs, however, they surely endowed the scaffolds with enhanced mechanical properties, improved osteogenesis bioactivity, better cytocompatibility as well as quick degradation rate. Reasonably adjusting BG ratios could balance the requirements of porous structure and bioactivity.

Taking into account the fact that since the 1970s frontal polymerization (FP) reactors in flow have been the subject of our study, the work gives a brief chronology of the development of FP reactors for the synthesis of high molecular polymers, polymeric hydrogels with cross-linked structure, their advantages and drawbacks. The reasons for the impossibility of the practical implementation of tubular FP reactors in flow for the synthesis of polymers are established. The possibility of implementation of tubular FP reactors for the synthesis of polyacrylamide hydrogels (PAH) capable of absorbing and releasing large amount of water is presented. The paper also presents some data on the methods for the synthesis of PAHs with prescribed properties in tubular continuous FP reactors by way of using nano-additives and regulating the kinetics of the synthesis process. As a result, the synthesis process of PAHs with the required properties both in the absorption and release of water, and in the physical-mechanical properties was carried out in frontal tubular-type reactors in flow, and the water absorption kinetic curves and physical-mechanical properties of the obtained hydrogels are presented.

In order to investigate the effect of the slot ends of the melt-blowing die on the three-dimensional airflow field distribution and the fiber draft, the numerical calculation was carried out. The computational domain of the slot die was established with Gambit, and the flow field was calculated using FLUENT. Compared with the experimental data collected by a hot-wire anemometer, the numerical calculation results are credible. The results show that the slot end face has a certain influence on the three-dimensional flow field distribution under the melt-blowing die. The air velocity and temperature in the center region are quite different from those near the slot-end face. As the distance from the center of the flow field increases, the velocity and temperature on the spinning line begin to decrease. The velocity and temperature distributions of the spinning lines in the central area and nearby areas are almost the same; the temperature and velocity values on the spinning lines near the slot end are the lowest. The distribution characteristics of the three-dimensional airflow field could affect the uniformity of the fiber diameter and the meltblowing products.

Pultrusion is considered to be a cost efficient method for developing composite structures. It facilitates the fabrication of uniform cross-section products with improved fiber alignment, mechanical properties, good surface characteristics, etc. In order to ascertain the crashworthiness, the pultruded composites shall be able to resist impact loads, and in this concern, the energy absorption capacity of the pultruded composites must be explored. This article presents the experimental and numerical investigation of the crushing behavior of polyester based pultruded composite with rectangular cross section. Pultruded rectangular tubes with e-glass/polyester composites have been developed for this study. The cross-section of the tubes was developed into two triggering profiles, the uniform edge around the section and the tulip pattern. The tubes were subjected to impact loads, and the effect of these triggering profiles on the energy absorption capacity of the tubes has been investigated. The testing of all composites has been carried out at three different impact velocities (10, 20 and 45 mm/min). The results have revealed the dependence of crushing behavior of the tubes on the loading velocity and the triggered profiles. Lower peak load and high specific energy absorption (SEA) was observed in the tube with tulip pattern profile. The results obtained from the simulation have also shown consistency with the real-time experiments.