Volume 39, Issue 5

The concept of residence time distribution (RTD) is crucial in many chemical engineering applications. In the case of co-rotating twin-screw extrusion, it is an important process parameter, particularly when dealing with reactive systems, degradation issues, or scale-up problems. In this review paper, after introducing the basic notions concerning RTD, the various measurement methods are detailed. Then, experimental results on the influence of the main parameters of the extrusion process (screw speed, feed rate, barrel temperature, screw profile, etc.) are presented. Finally, the various theoretical approaches to describe and/or predict RTD are reviewed.

The length and distribution of comonomers with short-chain branching (SCB) have a significant influence on the crystallization behavior and crystal structure of polymers, as well as the mechanical properties of the material. This study investigates the crystallization behavior and properties of linear low-density polyethylene (LLDPE) samples with similar density, molecular weight, and branching degree but varying SCB distributions. The results show that LLDPE with butene as the comonomer has a stronger ability to suppress crystallization compared to LLDPE with hexene as the comonomer due to its more uniform SCB distribution. Additionally, among LLDPEs with comonomers of octene, hexene, and butene, the LLDPE with the most uniform SCB distribution exhibits the weakest crystallization ability. Small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) results indicate that LLDPE with more uniform distribution of SCB has smaller long-period and more regular lamellar structure. Therefore, LLDPE with more uniform SCB distribution exhibits weaker inhibition ability towards crystallization, leading to less agglomerated phases and weaker phase separation, resulting in higher tear strength.

Zinc stannate (ZS) was prepared for flame retardant modified rigid polyurethane foam (RPUF). The flame retardancy and thermal stability performance of the modified RPUFs were investigated by limiting oxygen index (LOI), cone calorimeter (CONE), smoke density (Ds) test and thermogravimetric (TG) differential thermal analyzer. The LOI of RPUF5-7.5 AL/7.5 ZS with 5 wt% hydrolyzed keratin (HK), 7.5 wt% aluminum hypophosphate (AL) and 7.5 wt% ZS increased from 26.1 % to 27.2 %. At 50 kW/m 2 radiant intensity, RPUF5-7.5 AL/7.5 ZS had the lowest peak heat release rate (PHRR) and heat release rate (THR), which were 108.17 kW/m 2 and 2.56 MJ/m 2 , respectively. In addition, RPUF5-7.5 AL/7.5 ZS had the highest initial decomposition temperature of 191.24 °C and the largest activation energy (E) of 148.16 kJ/mol. Under flameless condition, the maximum Ds of RPUF5-7.5 AL/7.5 ZS was 31.25, and its light transmittance was also the highest, i.e., 57.89 %. Therefore, ZS/AL was selected as a synergistic flame retardant system to modify the RPUF, and promotes the development of high-performance building materials.

There is currently considerable interest in high-density polyethylene (HDPE)/ultra-high-molecular-weight polyethylene (UHMWPE) blends as recyclable all-polyolefin materials with favorable mechanical properties that can be processed by continuous melt-mixing. Optimal mixing is required to improve the mechanical properties of polymer blends by ensuring their dispersibility and low degradation. In the present study, we investigated the effects of mixing temperature on the dispersion and degradation behaviors of HDPE/UHMWPE blends. Neat HDPE and a HDPE blend comprising 5 % UHMWPE were obtained by melt-mixing while changing the input energy in an internal batch mixer under a nitrogen atmosphere. The temperature of the mixer was set at 200 °C for neat HDPE, and at 180, 200, and 220 °C for the HDPE/UHMWPE blends. Optical microscopy and thermal analysis revealed that the dispersion of UHMWPE in HDPE was accelerated at higher mixing temperatures. However, in the high input energy range, mixing at 200 °C resulted in the most favorable dispersion. Gel permeation chromatography and rheological measurements suggested that chain scission and branching/crosslinking due to degradation were accelerated at higher mixing temperatures, even when mixing in a nitrogen atmosphere. Chemiluminescence measurements suggested that chain scission and branching/crosslinking were caused by an initial oxidation reaction. Furthermore, for the same input energy, the maximum shear stress increased as the mixing temperature decreased, but the mixing time and thermal history increased as the mixing temperature increased. The results suggest that in a blend comprising HDPE and UHMWPE, mixing at the molecular level due to high temperature and fine dispersion of UHMWPE due to shear stress proceed simultaneously. On the other hand, the results also confirmed that degradation was more influenced by the promotion of oxidation due to high temperatures and prolonged mixing than by shear stress.

This work comparatively studied the electrical, morphological, and thermal properties of polyphenylene sulfide/multiwalled carbon nanotubes (PPS/CNT) composites prepared by compression molding (CM) and microinjection molding (μIM), respectively. The subsequent samples were termed as CM composites and microparts, respectively. Results revealed that the electrical conductivity of PPS/CNT microparts was lower than that of CM PPS/CNT composites, which was ascribed to the difference in shearing which affected microstructural evolution. In addition, SEM observations revealed that the distribution of CNTs became better in the PPS/CNT microparts, which was related to the prevailing higher shearing effect in μIM. The tensile strength of PPS/CNT microparts dropped for filler concentrations ≤2 wt% and it started to increase after reaching 10 wt%; in comparison with the PPS/CNT microparts, the tensile strength of CM PPS/CNT samples exhibited an opposite trend when the filler concentration was ≤3 wt%. After that, the tensile strength showed a monotonic increase with increasing CNT concentration. Both the uniform distribution of CNT and increase of crystallinity were crucial to improving the tensile strength of PPS/CNT moldings. This work showed that PPS/CNT moldings with good electrical conductivity and mechanical performance can be molded at relatively high filler concentrations, which is critical for applications in demanding engineering sectors.

In the present study, a simple yet efficient approach to the preparation of polystyrene nanocomposites based on a natural Algerian organophilic clay, called Maghnite, was addressed. The dispersion of the PS matrix polymer in the organophilic clay sheets was optimised. The resultant organic clays have been used for the preparation of PS nanocomposites by in situ polymerization. Both organic clays identified as Mag-CTA (0.5CEC) and Mag-CTA (2.5CEC) were used. The properties of the PS/Mag-CTA nanocomposites were studied using various physicochemical techniques (XRD, FTIR, TGA, TEM). Structural and thermal measurements were carried out on these materials. It was shown that the structural design of the surfactant influences both the morphological and thermal profile of the resulting nanocomposites. Optimization of the thermal behaviour was observed at a weight content of 5 % for both types of clay. The results of the gel permeation chromatography analysis of the nanocomposites showed that the presence of Maghnite-CTA reduced the average molecular weight as well as the average particle size of the PS. The best performance in terms of Young’s modulus, impact resistance and tensile strength was obtained from nanocomposites with 5 % organic content. The presence of organics causes the MFI of SP to decrease.

The development of heat dissipating composite materials for electronic systems can be expedited using alumina particles as modifiable polymer-matrix fillers. However, these composites are difficult to synthesize given the tradeoffs between thermal conductivity, insulating characteristics, and conduciveness to processing. To that end, the present study is focused on synthesizing environmentally friendly polyurethane films that could be cured by ultraviolet light within minutes, without requiring high-temperature heat treatment. Through the optimization of alumina modification, hybridization of thermally conductive fillers, filler content, and stirring time on the thermal conductivity of the polyurethane composites, this study improves the process for sustainability, low-cost, and convenient preparation. The experimental results confirmed that the use of surface modification and hybrid fillers is effective for enhancing the thermal conductivity, with the value of the polyurethane integrated with 50 wt% Al 2 O 3 and 5 wt% Al 2 O 3 –poly (catechol/polyamine) being 76.40 wt% higher than that of pure PU (0.44 W/mK). Additionally, the use of hybrid fillers resulted in superior mechanical and thermal properties (such as tensile strain, tensile strength, thermal expansion coefficient, and temperature resistance) compared with those of pure PU and films incorporated with only a single filler.

Zinc alginate (ZnAlg) was prepared and subsequently employed to modify ammonium ligninsulfonate-based polyurethane foams (PUFs). A range of analytical techniques, including thermogravimetry, integral programmed decomposition temperature, activation energy, smoke density, cone calorimetry and scanning electron microscopy, were employed to characterise the modified PUFs. The results demonstrated that PUFA15Z5 (15 % ammonium lignin sulfonate and 5 g ZnAlg) with the lowest mass loss exhibited the second-highest sample decomposition temperature (T 50 % ), second-highest peak temperature (T MAX2 ), IPDT and activation energy. Furthermore, the PUFA15Z5 sample exhibited the smallest smoke density (23.11) and the highest light transmittance (67.11 %). The peak heat release rate, total heat release, smoke production rate, total smoke release and four fire risk assessment indicators of PUFA15Z5 were the lowest, while its carbon residue was the densest. The results demonstrated that PUFA15Z5 exhibited the most favourable thermal stability, flame retardant properties and the lowest smoke toxicity. These findings provide a valuable reference for subsequent biomass-based flame retardant modified polyurethane foams (PUFs).

In this work, we have synthesized biocomposite films based on starch reinforced with microcrystalline cellulose (MCC) with different MCC/starch weight contents (0, 1, 3, 5, and 7 %). These films were characterized by various techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX), which showed dispersed and biocompatible structures for MCC and starch. It was found that the increase in MCC content (from 0 to 7 wt%) led to decreasing the water solubility, and reducing the absorption coefficients, transmission percentages and electrical conductivity. However, the improvement of dielectric and mechanical properties was demonstrated by decreasing the dielectric loss tangent and increasing the Young’s modulus, respectively making them suitable for dielectric and mechanical applications.

Additive manufacturing (AM) is a cost-effective method for fabricating structurally sound components. Fused filament fabrication (FFF) is a popular AM technique known for its design flexibility, minimal material wastage, and recyclability. Poly lactic acid (PLA) is a thermoplastic widely used in aerospace, biomedical, and automobile industries. Wood-PLA, incorporating wood fillers into PLA, finds applications in several industries. This research explores multilayered materials (MLM) for enhanced performance in various sectors such as aircraft, energy, and biomedical. Mechanical properties of MLM were investigated under different load conditions (tensile, bend, compressive). Properties simulated through Finite Element Method (FEM) showed minimal error (less than 1 %). Microscopic analysis, aided by scanning electron microscope (SEM) fractography, reveals a brittle mode of failure in the specimens. This study provides valuable insights into the mechanical behaviour of MLM, offering potential applications in diverse industries.