Volume 39, Issue 4

Microstructural analysis is an important technique to study the extent of interaction between metal fillers and polymers. The aim of this study is to review the investigations on the microstructural properties of metal-reinforced polymer composites. Scanning Electron Microscope (SEM) operating at a magnification range of 2,500× is typically used for examining the microstructure of the composites. Microstructural analysis reveals two key qualitative informations, dispersion and interfacial adhesion. It was observed from the review that flaky metal fillers will maximise dispersion and interfacial adhesion hence leading to improved mechanical, tribological, electrical, and thermal properties of the composites. Utilizing ternary metallic components helps to eliminate aggregation because the cohesion of metal particles is limited. It is important that future microstructural studies evaluate nano-sized fillers as compared to micro-sized ones. Also, it is important to quantitatively correlate the arrangement of the fillers to macro-scale properties and finite element analysis is an important tool that can help achieving this.

Increasing environmental awareness and concerns about global warming have resulted in a significant demand for sustainable and eco-friendly resources, such as naturally available fibers, that can be suitable alternatives to petroleum/synthetic materials such as glass, carbon and Kevlar in reinforced composites. The exploration of natural fibers as reinforcements in composites is increasing in popularity, particularly in the development of transport and household components. However, natural fibers also have a few limitations that should be addressed appropriately, including lack of compatibility between fiber-matrix, fiber swelling, excess absorption of moisture, resistance to chemicals and fire. Consequently, various processes have been used to improve the fiber surface, to obtain a better fiber–matrix interface. The primary objective of this work is to review the impact that a 5 % NaOH (sodium hydroxide) treatment has on the chemical, mechanical, and thermal properties of natural fiber-reinforced composites (NFRC).

In this work, a new material (PP-Mag) was manufactured using pine pollen (PP) and cetyltrimethylammonium bromide (CTA-Mag). By combining PP and Maghnite with an epoxy resin (EP), innovative nanocomposite materials was developed. With different blend compositions, the effect of EP on the mechanical properties, polarisation tests, salt spray tests and morphological characteristics of the blends was studied. The storage modulus ( E ′) of EP is 2179 MPa, which increases to 2361 MPa with increasing PP-Mag content. The mechanical properties of the blends containing EP/wt%PP/Mag showed an improved performance due to a better adhesion between the two phases when EP is incorporated. It was shown that the PP/Mag materials present in the matrix improve the corrosion resistance according to the different polarisation tests and the salt spray test.

A hybrid composite incorporating veli karuvelam and peepal fibers was fabricated, with the addition of nanosilica as a filler to enhance composite performance. The impact of nanosilica and layering sequence on the physical properties of the composites was investigated. Initially, two types of hybrid composites i.e. peepal/veli karuvelam/peepal (PVP) and veli karuvelam/peepal/veli karuvelam (VPV) were developed by means of hand layup method, varying the layering sequence of veli karuvelam and peepal fibers. The PVP composite was identified as the most promising based on tensile strength (71 MPa), attributed to the optimal packing of high-strength peepal fibers. Subsequently, nanosilica was incorporated into the PVP composite at different weight percentages (1, 2 and 3), and its influence on composite performance was analyzed. The PVP composite containing 2 wt% SiO 2 showed impressive mechanical properties, with a tensile strength of 76 MPa, a flexural strength of 104 MPa, an impact strength of 4.5 kJ/m 2 , and a hardness of 89 on the Shore D scale. The findings indicate that a PVP composite containing 2 wt% SiO 2 has potential for use in engineering applications.

Extrusion is a key process in mechanical recycling. In a degassing step, volatile components, including all impurities and moisture, are removed from a polymer melt to ensure consistently high quality of the recyclates. Predicting devolatilization performance is therefore of interest in the design of degassing screws; in the plastics industry, it also plays an important role in the transition from a linear to a circular economy. Using two different devolatilization models, we first modelled the degassing process of a lab-scale twin-screw extruder and an industrial-scale recycling single-screw extruder. We then predicted the devolatilization performance of both machines, validated the results with experimental data obtained from emissions tests carried out with post-industrial and post-consumer polypropylene materials and performed linear regression analysis to compare our two models in terms of predictive quality. Our results showed that both models are equally suitable for reliable prediction of the devolatilization performance.

This research investigates the production of composite materials by utilizing a polystyrene-based resin (PBR) as the matrix and a blend of coconut fiber (CF) and rubber tire (RT) as fillers. The composites were produced in varying proportions, and their mechanical and chemical properties were characterized through hardness tests, Fourier-Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. The findings highlight the notable influence of filler type and proportion on the mechanical and chemical attributes of the composites. The hardness tests demonstrated a substantial enhancement in composite hardness with the incorporation of CF and RT fillers, with CF exerting a more pronounced effect. FTIR analysis disclosed the presence of aromatic and aliphatic groups in all composites, and the introduction of CF and RT particles led to the emergence of additional peaks. EDS analysis indicated that carbon was the predominant element in all composites, followed by oxygen, while the SEM images revealed a heterogeneous microstructure for all composites, with good dispersion of CF and RT particles in the PBR matrix. The resulting composites exhibit potential applications in diverse fields such as construction, automotive, and packaging.

In this work we investigate the influence of closed (“C”) or open (“O”) extrusion degassing, and low (5 MPa – “L”) or high (90 MPa – “H”) holding pressure during injection molding on the properties of wood-plastic composite (WPC) based on high-density polyethylene (HDPE) flakes compatibilized with 5 wt% maleic anhydride-modified polyethylene (MAPE), 5 wt% lubricant (Struktol ® TPW 113), and 40 wt% cashew nutshell powder (CNSP). Two reference compounds were extruded with closed degassing and injected at 90 MPa of holding pressure: (1) HDPE flakes extruded with 5 wt% MAPE and 5 wt% Struktol ® TPW 113 (HDPEad_C-H) and (2) HDPE flakes previously melt mixed in an internal mixer with 5 wt% CNSL (HDPEr/5CNSL) and then extruded with the same additive content (HDPEad/5CNSL_C-H). At 90 MPa holding pressure, the extract content of WPC slightly increased and CNSL acted as a lubricant and poor plasticizing agent, reducing the crystallinity and density of the additivated matrix (HDPEad_C-H), increasing the flow rate without significantly changing the tensile strength. On the other hand, low holding pressure (5 MPa) favored the volatilization and expansion of the residual CNSL in the WPC, which acted as a blowing agent improving filling of the mold cavity and avoiding sink marks. Sample extruded with open degassing (atmospheric pressure) did not significantly change the extract content, but favored CNSL diffusion from particles to matrix, which subsequently during injection molding led to its entrapment at the interface, resulting in low adhesion, especially at high holding pressure that hinders CNSL expansion and vaporization. These findings contribute to understand the role of residual CNSL of CNSP in WPC properties and thus, to strengthen the plastics recycling chain and reduce carbon footprint.

Intraocular lens (IOL) made on Polymethylmethacrylate (PMMA) has been irradiated by a UV lamp at different exposure times, in air and at room temperature. The macromolecular modifications induced in the lens have been investigated using attenuated total reflectance (ATR) coupled to Fourier transform infrared (FT-IR) spectroscopy and Optical spectroscopy. Particular attention was devoted to the study of chemical modifications by UV irradiation, which induced chain scissions in the superficial PMMA layers. Results demonstrated that the lens transmission to the visible radiation is not particularly reduced by a long exposition to UV radiation at a fluence of 200 mJ/cm 2 , up to 19 h.

In response to the problems of 3D printing, such as uneven wire discharge and easy clogging of printing nozzles in FDM (Fused Deposition Modeling) printing technology, this paper develops a screw extrusion 3D printing melting deposition system based on simulation. The simulation results show that the maximum deformation of the screw occurs at the tail end, with a maximum value of 0.04 mm, while the fluid pressure and the pressure on the surface of the screw gradually increase along the direction of extrusion, and the maximum pressure occurs near the nozzle, with a value of 0.13 MPa. The fluid pressure is positively correlated with the screw speed and negatively correlated with the screw pitch. The fitting formula is obtained by numerical simulation of the screw speed and the flow velocity at the nozzle outlet. Using a self-made screw extrusion 3D printing equipment, relevant experiments are conducted to explore the influence of different layer thicknesses and line spacings on the mechanical properties of printed samples, as well as the influence of printing speed on surface quality. It is found that layer thickness has a significant impact on the bending strength of printed samples, with a maximum value of 24.74 MPa and a minimum of 19.21 MPa. The bending strength decreases by 28.79 % from 0.6 mm to 1.0 mm layer thickness. The line spacing has a significant impact on the tensile strength of printed samples, with a maximum value of 27.22 MPa and a minimum of 21.16 MPa. As the printing speed increases, the surface roughness of the printed piece also gradually increases from Ra = 389.28 μm at v  = 30 mm/s to Ra = 535.45 μm at v  = 70 mm/s, an increase of 37.55 %.