Volume 39, Issue 1

Polylactic acid has the potential to be an alternative to petroleum-based materials in the food packaging industry. In this study, the effect of zinc oxide nanoparticles, polyethylene glycol 400, and Tween 80 as plasticizers on the properties of polylactic acid films was investigated. In order to study the mechanical properties more accurately, the tests were repeated for four months. An experimental design method was used to investigate the effects of additives on the measurement factors and finally to choose the optimal combination with the help of the TOPSIS technique. The results showed that the addition of different materials increased the opacity, most of which being related to P400/ZnO (6.82 ± 0.07 mm −1 ). The presence of plasticizers increases the hydrophilicity of the film and the water vapor permeability. The highest contact angle (85.33° ± 4.00) and the lowest water vapor permeability (0.074 ± 0.002 g mm/kPa h m 2 ) were related to neat PLA film. The lowest modulus of elasticity, the highest tensile strength and elongation at break were related to P400/T80/ZnO (1.18 ± 0.17 GPa, first month), PLA/ZnO (96.28 ± 3.17 MPa, fourth month), and P400/ZnO (76.82 ± 27.22 %, first month), respectively. The effect of plasticizers was significant in most of the measurement factors, but the effect of nanoparticles was significant in some cases such as opacity and contact angle. The results of an ANOVA analysis showed that the effect of film type on the mechanical properties was significant, and the effect of storage time was only significant on the elongation at break. According to the results obtained from the TOPSIS technique, P400/ZnO was chosen as the combination with the best features among the produced films.

The modified polyurethane foam (PUF) with ammonium lignosulfonate was prepared by one-step water foaming method. The effects of ammonium lignosulfonate on its thermal stability and smoke suppression were investigated by thermogravimetric analysis, pyrolysis kinetics analysis, smoke density (Ds) and smoke toxicity analysis. The results showed that the addition of 15 % ammonium lignosulfonate (PUFA15) had the lowest mass loss of PUFs and the highest integral programmed decomposition temperature (870.8 °C). Its activation energy was the highest according to the Flynn-Wall-Ozawa method (110.1 kJ/mol), Kissinger method (181.1 kJ/mol), Starnk method (106.3 kJ/mol) and Coats-Redfern method (149.7 kJ/mol). In addition, PUFA15 had the lowest Ds (34.43) and the highest transmittance (66.74). This indicated that PUFA15 had good thermal stability and smoke suppression properties. The research results had a reference value for exploring the production of environmentally friendly PUF by biomass modification.

Rigid polyurethane foams (RPUFs) were prepared using biomass soybean oil-based polyol and ammonium polyphosphate (APP) as raw materials. The effects of APP on the thermal stability and combustion performance of soybean oil-based polyol-modified RPUFs were investigated by thermogravimetric analysis, pyrolysis kinetic analysis, limiting oxygen index (LOI) test, cone calorimetry (CONE), scanning electron microscopy (SEM), and smoke density (Ds). The results showed that the modified RPUF with 20 wt% APP (RPUF-S3-20) had the lowest mass loss, the highest integrated programmed decomposition temperature and the highest activation energy. In addition, RPUF-S3-20 had the lowest Ds (30.9), the highest light transmittance (61.4 %), the lowest heat release rate (602.7 kW/m 2 , 506.8 MJ/m 2 , and 847.3 kW/m 2 ) and the total heat release (18.3 MJ/m 2 , 21.4 MJ/m 2 , and 31.4 MJ/m 2 ), which showed that RPUF-S3-20 had good thermal stability and flame retardant performance. The current results can provide an effective reference for the preparation of environmentally friendly RPUF by bio-based modification.

In state-of-the-art predictive engineering software for injection molded fiber composites, it is challenging to discuss the effect of fiber properties, including fiber content and aspect ratio, on the shell-core fiber orientation and anisotropic flow front. Recently, the flow-fiber coupled model of informed isotropic (IISO) viscosity was proposed for simulating the realistic flow-induced fiber orientation. At present, one attempts to improve the IISO viscosity in relation to fiber content and aspect ratio. Therefore, injection molding simulations of 30 wt% and 50 wt% short glass fiber-reinforced Polyamide66 (30 wt% SGF/PA66 and 50 wt% SGF/PA66) are performed in the IISO flow-fiber couple 3D-FVM (three-dimensional finite volume method) computation under the fixed aspect ratio of a r  = 20. As a result, the predicted fiber orientation distributions are in good agreement with related experimental data, while the core width is increased with fiber contents. In addition, the anisotropic ear flow occurs at the higher content. Based on shear viscosity of 30 wt% SGF/PA66, one can directly alter fiber content as 50 wt% SGF/PA66 in the IISO computation to anticipate the reliable trend of fiber orientation and flow behavior. When the a r  = 20 short fiber is lengthened as the a r  = 50 long fiber, the core obviously becomes the wider. It is significant to investigate the difference between the decoupled and coupled computation, as well as the influence of the flow-fiber coupled and fiber orientation model parameters.

This study aimed to develop novel hybrid composites with graphene (Gr) fillers incorporated in the epoxy (E) matrix with Caesar weed fiber (CF), and roselle fiber (RF) as reinforcements. Compression molding methods were used to fabricate hybrid composite materials with a variable-weight graphene filler in a constant fiber epoxy matrix. On the basis of the results, the mechanical characteristics of the composite with 6 wt% Gr exhibited the greatest flexural strength, tensile strength, and impact strength. This occurred because 6 wt% Gr particles are more uniformly dispersed in an epoxy matrix, resulting in better compatibility between reinforcement and matrix, thus increasing the mechanical properties. The composite with 8 wt% Gr filler reinforcement had the maximum hardness rating and the lowest percentage of water absorption. According to the results, adding graphene fillers to the CF/RF/E composite significantly improved the mechanical and water absorption performances. Scanning electron microscopy was used to examine the surfaces of the fabricated samples. The weight fraction of the graphene filler was optimized to enhance the mechanical properties of the composite for use in various engineering applications, such as automobile, defense, marine, sports, and musical instruments.

This study aimed to evaluate the impact of nanoparticle inclusion and patch size on the bonding performance of single-strap repaired glass-reinforced composite plates through experimental investigations. Epoxy adhesive was modified with three different nanoparticles: nano-silica (NS), nano-graphene (NG), and nano-clay (NC) at varying weight contents. The patch repair performance of the test samples was evaluated using two patch ratios (Patch diameter ( D )/Hole diameter ( d ) = 2 and 3) to explore the influence of patch size on repair effectiveness. GFRP composite base plates having a 10 mm diameter hole in the middle were patch repaired by using patches with the same material. Tensile tests were conducted to compare the tensile performance of the repaired composite samples, and the results were compared with the samples with and without holes. Based on the findings, it was noted that samples with a larger patch ratio ( D / d  = 3) can withstand higher tensile loads compared to those with a patch ratio of 2. Moreover, it was found that the specimen repaired with 3 % by weight NC-filled epoxy adhesive showed the greatest increase in tensile load value. This increase was recorded at both patch rates, with a percentage improvement of 2.8 and 19.54 % compared to pure epoxy adhesive. Also, it was observed that when the patch ratio was 3, the 3 % NS-filled adhesive showed an increase of 3.3 %. On the other hand, all combinations of NG-filled adhesive showed a decrease in maximum tensile load values.

The production of thermoplastic pellets using underwater die-face pelletizers is a widespread process in the thermoplastics compounding industry. One major challenge in this process is pellet agglomeration, which occurs when the polymer is pliable or easily deformed under heat. To tackle this issue, the non-Newtonian flow of a polymer, along with the turbulent flow of heating oil and heat transfer through the die, are modeled using three-dimensional (3D) computational fluid dynamics (CFD) calculations in ANSYS Fluent. The computational model is validated by comparing its predictions of temperature and pressure using two models with and without a slip method, to experimental measurements from an industrial-scale pelletizer, resulting in a maximum error of <3 % for temperature and <16 % for pressure. The efficiency of the underwater die pelletizer is typically evaluated based on the rate at which it produces pellets. Minor variations in operational parameters, such as the inlet mass flow rate and temperature of the polymer, the temperature of the heating oil, and the water temperature, can greatly affect the quality of the final product. Firstly, contours of pressure, velocity and temperature are presented to understand their impact on pellet agglomeration. However, to more specifically link pellet quality, i.e. pellet agglomeration rate, to the input conditions, the study develops a non-dimensional parameter called the pellet agglomeration number (PAN), as a non-linear function of three other non-dimensional numbers: Reynolds number, Euler number, and a non-dimensional temperature. The values of PAN at the exit and inlet are shown to correlate well with the experimentally measured pellet agglomerations, thereby demonstrating the usefulness of PAN in not only differentiating between good and bad pellet quality but also determining apriori the appropriate operating conditions leading to fewer pellet agglomerations in commercial pelletizers.

Corotating twin-screw extrusion is widely used for many applications in mixing and compounding. While the flow conditions in the different screw elements are now well known and accurately modeled, the melting mechanisms, i.e. the transition between solid and molten polymer, are much less understood and are still the subject of debates. In this review paper, experimental observations from the literature are first presented and commented, followed by the proposed theoretical approaches. It will be concluded that a satisfactory model considering the different mechanisms involved in the melting step has yet to be elaborated, unlike what exists for the single screw extrusion.

Bamboo and its hybrid composites were made using the hand lay-up method to evaluate the change in mechanical and physical properties that occurred through filler addition. Density measurements and tensile test results showed an increment in values when a certain percentage of silicon carbide (SiC) was added. As the SiC percentage grows from 0 to 6 %, the density of the hybrid composite increases from 1.15 to 1.36 gm/cc whereas tensile strength increases from 37 MPa to 42 MPa when 4 wt% SiC is added in 20 wt% of the bamboo composite. The scanning electron microscopy (SEM) analysis of tensile fractured samples further supported the improvement in tensile characteristics. To examine the impact and hardness characteristics, composites were subjected to the Charpy impact test and hardness test. 4 wt% of SiC addition in 20 wt% of the bamboo composite decreased the impact strength from 28.79 to 27.43 (×10 −3  kJ/m 2 ) and increased the hardness from 44 to 55 Hv. The composites’ water absorption behavior demonstrated that the addition of filler lifts the composite’s resistance to absorbing water, preserving the composites’ dimensional firmness and mechanical qualities.