Volume 43, Issue 4

Environmentally friendly foams have been studied extensively to handle the plastic pollution caused by disposable tableware. Herein, biodegradable poly (lactic acid) (PLA) – poly (butylene adipate-co-terephthalate) (PBAT) composites were first fabricated by melt blending, in which a reactive chain extender (ADR) was incorporated to enhance the interfacial compatibility and melt strength, a nucleating agent (TMC) was applied to improve the crystallinity. Subsequently, the foaming behavior of the composites was investigated via supercritical CO 2 foaming. Specifically, a spherulite and shish-kebab-like nanoporous structure was observed from PLA and PLA/TMC foams, respectively, when the soaking temperature was far below melting temperature. With an increase of foaming temperature, the unmelted completely crystals served as physical cross-linking points, also contributing to a high melt strength. Combined with chain extension reaction of ADR, the PLA–PBAT/ADR/TMC foams showed the largest cell diameter and expansion ratio, which were 19 μm and 8.9, respectively. Furthermore, the heat resistance of PLA–PBAT/ADR/TMC foams was also significantly improved, owing to the high crystallinity induced by TMC. Consequently, the composite foams with superior heat resistance and toughness were obtained to broaden its application as biodegradable disposable tableware for hot food.

Carrageenan fibers crosslinked with trivalent metal ions (Al 3+ or Fe 3+ ) were prepared into carrageenan fiber paper (Al/CAP, Fe/CAP) by the Rapid Kothen method, and their flame-retardant mechanism and flame retardancy were studied through LOI, VF, SEM, CONE, and TGA testing. The results showed that Al/CAP exhibited good flame retardancy and thermal stability, and its LOI value reached 52%. Meanwhile, the afterflame time and afterglow time of Al/CAP were 0 and 1 s, respectively, which indicated that it was not ignited and almost had no smoldering phenomenon. The flame-retardant performance of Fe/CAP is inferior to that of Al/CAP, with LOI of 32, but the total smoke emission (TSP) of Fe/CAP is lower in cone calorimetry test. Thus, CAPs (especially Al/CAP) can be widely used in the flame-retardant paper industry, due to their flame retardancy and environmental protection.

In this study, multi-wall carbon nanotube (MWCNT) reinforced acrylonitrile butadiene styrene (ABS) nanocomposite filaments are produced. Filaments are examined through thermogravimetric analysis (TGA) and definitive scanning calorimetry (DSC) analysis. Produced nanocomposite filaments are used in the fused deposition modeling (FDM) process to manufacture parts. Wear tests are conducted on 3D-printed parts using wear test apparatus with an attached heating module under different ambient temperatures. Hence, the influence of CNT reinforcement, along with different FDM process parameters and varying test conditions on the wear behavior of 3D-printed ABS-CNT parts, are examined. Worn surfaces of the specimens are examined by scanning electron microscopy (SEM). Nonlinear autoregressive exogenous (NARX) models are proposed for the prediction of the wear behavior of 3D-printed ABS-CNT nanocomposites. While wear rate is taken as output, ambient temperature and amount of nanofiller are accounted as input parameters along with the variation of coefficient of friction (COF) which is obtained from measured frictional force and three input-one output model structure is proposed for NARX. The use of multiple input-single output (MISO) model structure and examining the wear behavior of 3D-printed ABS-CNT samples under different wear test conditions with different FDM process parameters are the novelties in this work.

The blended composites with ultra-high molecular weight polyethylene (UHMWPE) as the matrix polymer, sodium polyacrylate (PAANa), and tetraphenyltin (Ph 4 Sn) as fillers were prepared by hot compression molding process. The friction and wear behavior of GCr15 balls with composites mating pairs under the seawater environment was explored, and the friction and wear mechanism was analyzed. The results show that adding PAANa, a polyelectrolyte material, can effectively reduce the friction coefficient of UHMWPE/PAANa/Ph 4 Sn composites. The wear resistance of composites increased significantly with increasing Ph 4 Sn content compared with pure UHMWPE, and the best wear resistance was observed at 1% content. The primary wear mechanism of UHMWPE/PAANa/Ph 4 Sn composites changed from adhesive wear of pure UHMWPE to plastic deformation at lower PAANa and Ph 4 Sn contents and finally to adhesive wear and spalling. This work provides a theoretical basis for preparing and applying other polymer blend composites.

High density polyethylene (HDPE)/graphene nanocomposites were successfully synthesized by compounding of HDPE, as polymer matrix, with hexamethylenediamine functionalized graphene. The resulting nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA) techniques. SEM characterization confirmed the good dispersion (homogeneous and uniform) of graphene in the polyethylene matrix. The TGA technique revealed a slight improvement in thermal resistance. Functionalized graphene improved a better thermal stability of HDPE (up to 6 °C) than non-functionalized graphene (up to 2 °C). Mechanical tensile and torsion tests showed that HDPE/functionalized graphene nanocomposites exhibit high tensile strength and low torsional strength compared to HDPE/non-functionalized graphene nanocomposites. Compared to pure HDPE, the Young’s modulus increased by 80% and 30%, whereas, the torsion modulus increased by about 34% and 44% for the HDPE/functionalized and HDPE/non-functionalized graphene, respectively. Regardless of this increase, it can be seen that the torsion modulus of HDPE/non-functionalized graphene is much higher than that of HDPE/functionalized graphene.

In the thermal energy storage area, microencapsulated phase change material (MPCM) is getting more popular among researchers. When phase change materials (PCMs) shift from one phase to another at a specific temperature, a significant quantity of thermal energy is stored. The PCM application focuses on upgrading worldwide energy conservation efforts in light of the rapidly dwindling fossil fuels. The thermal energy supplied by PCM is significantly influenced by the choice of supporting materials and encapsulation methods. A solution to the volume change issues of PCM, phase separation, and leakage is the PCM microencapsulation technique. One of the most common methods to increase the effectiveness of thermal storage material is attained by using PCM with microencapsulation. The preparation processes and thermal characteristics of the MPCM are summarized in this paper. This paper gives information about MPCM with its types, properties, testing, and characterizations. Tables describe specific examples of PCM with thermal properties. Applications in various fields are defined. This review gives as much information to help and be useful for new researchers in the field of thermal management systems to guide their future research.

Fatigue crack growth in polymers is analyzed using the two-parametric approach. Polymers deform by crazing, viscoelastic deformation, or brittle fracture, contributing to crack growth. The analysis shows that irrespective of the nature of the deformation of the material ahead of the crack tip, the crack growth rate data can still be represented by the L-shaped curves in the Δ K – K max plane defining two limiting variables Δ K * and K max * . Thus, as in metals and alloys, the L-shaped curves depict the intrinsic fatigue behavior. The analysis further confirms that the load ratio effects in all materials are intrinsic to fatigue. A simple method for the prediction of these L-shaped fatigue curves is proposed.

The formation of a stable gas layer is to have a significant effect on polymer gas-assisted extrusion (GAE). Previously, for vertical extrusion forming, the gap intake method was used, which tends to result in very short stabilization times for the gas layer. In this study, the effect of two gas intake modes was compared based on horizontal sheet extrusion. The results show that stabilization of the gas layer is easily achieved in the vertical gas-assisted die by introducing gas first. However, when using parallel die, the gas distributes the melt uniformly along the surrounding velocity and the gas layer can be stable for a long time. Moreover, disrupting the process sequence also makes it easy to achieve gas layer stability without affecting the tability of the gas layer in the subsequent extrusion. And, during low-speed extrusion, the flow inertia of the polymer melt is used to extend the flow channel of the gas-free–assisted section into the gas-assisted section to overcome the gravity of the polymer melt and smoothly extrude it in the parallel gas-assisted die. The parallel die can be considered for the production of GAE of daily profiles and can be used to improve quality.