This study investigates the morphology and thermo-mechanical properties of cross-linked polyethylene (PEX) pipes for potential use in high-temperature borehole thermal energy storage systems. Particular attention is given to a novel type of PEX pipe produced through photoinitiated cross-linking (PEX-e). Two formulations, PEX-e1 and PEX-e2, were analyzed and compared to peroxide-cross-linked polyethylene (PEX-a) and non-cross-linked bimodal polyethylene (PE100) pipes. The degree of cross-linking was evaluated via gel content, while cross-link density and molecular weight between cross-links were determined using dynamic mechanical analysis (DMA). Phase composition and molecular mobility were explored through 1H static nuclear magnetic resonance (NMR), and the melting and crystallization behavior was assessed by differential scanning calorimetry (DSC). Oxidative stability and degradation were examined by using Fourier transform infrared (FTIR) spectroscopy, oxidation induction time (OIT) measurements, and thermogravimetric analysis (TGA). Both PEX-e formulations achieved satisfactory cross-linking degrees and exhibited remarkable OIT values. However, significant differences in cross-link distribution were noted, with PEX-e2 showing a less uniform dispersion of cross-links, which resulted in a lower storage modulus. FTIR analysis indicated that oxidation products were formed in PEX-e1 during cross-linking, highlighting the need for further optimization of the formulation and processing conditions.

This study presents a comprehensive evaluation of the thermo-oxidative stability of crosslinked polyethylene (PEX) pipes designed for borehole thermal energy storage (BTES) systems, with a particular focus on a novel PEX type produced via a photo-initiated crosslinking process (PEX-e). Two formulations, PEX-e1 and PEX-e2, were assessed and compared to commercial peroxide-crosslinked polyethylene (PEX-a) and bimodal polyethylene (PE100) pipes. The pipes were aged in distilled water at the intended BTES service temperature for 210 days, with periodic analyses conducted to monitor antioxidant (AO) depletion and the formation of degradation products. Advanced analytical techniques were employed, including Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy, gel content analysis, colorimetry, differential scanning calorimetry (DSC), oxidation induction time (OIT), and dynamic mechanical analysis (DMA). FTIR analysis revealed the presence of degradation-related peaks on the pipe surfaces, while the formation of oxidation products in the bulk material was limited. Phase composition analysis showed that physical ageing dominated during the first 30 days, leading to increased crystallinity and enhanced lamellar thickness. Over time, chain scission emerged as the primary degradation mechanism, resulting in molecular weight reductions, with PEX-a being the most severely affected. No abrupt changes in phase composition or mechanical properties were observed after 210 days of ageing, indicating that the pipes remained in the induction phase of degradation. Interestingly, despite their high OIT levels, both PEX-e formulations exhibited accelerated AO depletion during prolonged exposure, suggesting the need for further optimization of PEX-e formulations to ensure long-term stability under demanding BTES conditions. 

The aim of this study was to develop and additively manufacture polypropylene-hemp fiber (PPHF) composites, which were composed of polypropylene (PP) and hemp fibers (HF) in various percentages (5%, 10%, and 20%). The objective was to examine the mechanical properties and water absorption behaviors of extruded PP, conventional filament PP and PPHF composites. The findings of the flexural and tensile tests provided important valuable information. In comparison to the other materials examined, extruded PP had the highest flexural modulus and strength, but filament PP had the lowest mechanical properties. The results showed that the 5% hemp PP composite exhibited the highest tensile strength, and the 20% hemp PP composite showed the highest Young's modulus. These results highlight how crucial hemp fiber content is in modifying the mechanical characteristics of a polymeric material to obtain the material with desirable properties for specific industry requirements.

The complexity of the vulcanized rubber makes it difficult to be degraded by microorganisms. It is believed that a microbial consortium can improve the efficiency of the biodegradation process. Fertile soil houses a plethora of microorganisms with innate ability to adapt to various chemical substances come into contact with its texture. Consequently, a soil sample which was in direct contact with tire wastes for more than 13 years was employed in this work to enhance the biodegradation of natural rubber (NR) gloves. The active soil microorganisms associated with the NR latex degradation were isolated and identified using 16S rRNA gene sequencing method. The biodegradation of NR gloves in the soil sample containing these bacteria was investigated and the results represented 87% and 79% weight loss in the examination and surgical gloves after 12 months of treatment, respectively. The total biodegradation was achieved after 13 and 15 months which was nearly half of the reported time in the landfill processes. Thermal gravimetric analysis (TGA) showed 15% incremental weight decrease for the treated samples after three months in comparison with the blanks and the FT-IR spectra approved the breaking of the cross-link sulfur bonds as well as the formation of carbonyl groups which indicated oxidative cleavage of double bonds of the polymer chain. A chemical mechanism for the biodegradation was suggested based on the obtained results to explain the higher efficiency of biodegradation in this work.

Green composites, renowned for their biodegradable and recyclable attributes, have recently gained substantial prominence. Their sustainability, eco-friendliness, and lightweight characteristics position them as a compelling alternative to conventional plastic-based materials. This study delves into the mechanical performance, encompassing tensile, flexural, and Charpy impact test properties, of jute and flax thermoplastic composite laminates. Additionally, it explores the flexural behavior of sandwich composites reinforced with jute and flax fabrics individually. To accomplish this, we manufactured various composite laminates, including jute/PP, flax/PP (64.2 % fiber mass fraction), flax/PP (45.0 % fiber mass fraction), and plasma-treated flax/PP (PTF/PP) composite laminates using compression molding techniques. We also crafted sandwich composites by integrating flax and jute natural fabrics as reinforcements into a polypropylene (PP) matrix for the sandwich surface layer, along with recycled polyethylene terephthalate (PET) foam as the core material. This allowed for a comprehensive comparative analysis of their functional properties. In addition to mechanical testing, the differential scanning calorimetry (DSC) analysis was conducted on various composite laminates to evaluate the crystallinity levels and melting behavior of PP within these diverse formulations. Further characterizations included Fourier transform infrared (FTIR) spectroscopy and digital imaging analysis. Our experimental results unequivocally demonstrated the superior performance of Flax/PP composite laminates over Jute/PP composite laminates in terms of flexural, tensile, and impact properties. In the context of sandwich composites, Flax/PP/PET foam exhibited the highest force resistance, along with superior bending strength and modulus when compared to Jute/PP/PET foam. Notably, Jute/PP/PET foam displayed a higher incidence of delamination and breakage. Interestingly, both sandwich composites demonstrated nearly identical properties in the impact test. Furthermore, plasma treatment of flax composite laminates had a beneficial effect on specific mechanical properties, leading to an 8.6 % enhancement in flexural strength (54.09 MPa) compared to the performance of flax/PP (45.0 % fiber mass fraction) laminate.

Nanocomposites of latex and nanocellulose represent a significant advancement in material science. The research explores the semi-batch approach for the synthesis of colloidal nanocomposite latexes, facilitating scalability and reproducibility. The urgent need to replace non-degradable plastics with sustainable alternatives has driven research towards biobased and biodegradable materials. The colloidal nanocomposite latex demonstrates potential as a coating for barrier applications. We have been conducting research on scalability of manufacturing colloidal nanocomposites of vinyl acetate and cellulose nanocrystals. Chemical bonds between poly (vinyl acetate) and CNCs, stability, swelling, drying rate, water vapor transition rate, and topography of the final film have been investigated. The colloidal nanocomposite demonstrates potential as a coating on cellulosic substrates such as paper and cardboard. The colloidal nature of the nanocomposite allows for uniform coating deposition, ensuring consistent barrier performance across the substrate surface. Higher drying rate and lower water vapor transition rate for certain periods measured for nanocomposites. There was no obvious aggregation for CNCs which have been extracted through sulfuric acid hydrolysis. The reduction of hydroxyl groups showed successful bonding between CNCs and poly (vinyl acetate). Immersing the films of nanocomposites in water showed stability of the film, while poly (vinyl acetate) film disintegrated by water adsorption. Cellulose nanocrystals changed the surface topography of the films, and the roughness increases by increasing the dosage of CNCs. This research contributes to the development of eco-friendly alternatives to non-degradable plastics, paving the way for a more sustainable future.

Polyethylene (PE) is a low-cost and versatile material for pipe applications. However, when it comes to at elevated temperatures, the use of PE is restricted due to its propensity to crack under stress and to undergo thermo-oxidative degradation reactions (ageing)1. Cross-linked polyethylene (PEX) has been appointed as a promising alternative to solve these limitations1. There are several different cross-linking processing methodologies for polyethylene pipes. The most usual methods are based on peroxide (PEX-a), silane (PEX-b) and irradiation (PEX-c). Additionally, photo-induced cross-linking (PEX-e), has recently garnered attracted significant commercial interest, but there is still very little information in the literature regarding this novel material. Recent findings appoint to hot water as being the key component element driving the ageing mechanism in PEX-a pipes used for hot water transportation. However, further investigation of the effects of ageing on PEX properties over time is of high importance. Accordingly, the present work aims to evaluate the properties of different types of PEX pipes as a function of ageing. PEX-a, two formulations of PEX-e and PE pipe samples were submersed in distilled water at 95°C for 150 days. Samples were removed periodically and the effect of degradation on the properties was measured by differential scanning calorimetry (DSC), oxidation induction time (OIT), dynamical mechanical thermal analysis (DMA) and tensile tests. Initial results showed that the OIT values for PEX-a before ageing were considerably lower than for the other materials but remained overall the same after 60 days of ageing. For the two formulations of PEX-e, a considerable decrease in OIT was observed, indicating that stabilizing additive hydrolysis was high for this PEX type under these conditions.