Polymer composites are widely used in indoor and outdoor applications owing to their high strength-to-weight ratio, corrosion resistance, and design flexibility. However, exposure to environmental factors such as ultraviolet (UV) radiation, humidity, temperature fluctuations, and biological agents significantly affect their long-term durability and performance. In this review, we comprehensively examine the degradation mechanisms of polymer composites under both natural and accelerated weathering, with particular emphasis on degradation mechanisms, characterization techniques, and durability assessment. We critically discuss the fundamental degradation mechanisms, including photo-oxidation, hydrolysis, polymer chain scission, crosslinking and interfacial debonding. We also evaluated accelerated weathering techniques, conducted under standardized testing conditions, for their ability to simulate long-term outdoor exposure within significantly shorter timeframes, by controlling key environmental parameters such as UV radiation, humidity, and temperature. We also examine the influence of reinforcements, including natural fibres, synthetic fibres, and nanofillers, on the weathering resistance of polymer composites. Attention is given to natural fibre–reinforced composites because their inherent hydrophilicity promotes moisture absorption, accelerating degradation and weakening the fibre–matrix interface. Furthermore, we critically evaluate the effects of weathering on the mechanical properties, crystalline structure and barrier performance of polymer composite films, and discuss recent advances in enhancing weather resistance through hybridization, surface modification, and the incorporation of stabilizing additives. Finally, the review highlights the key challenges and future research directions for the development of durable, high-performance, and sustainable polymer composite systems for long-term outdoor applications.

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Electrospinning is a widely used technique for manufacturing nanofibers from polymers. The formation of continuous fibers during the drawing of a viscous solution typically depends on entanglements between polymer chains, making thermoplastics the preferred choice. In this study, we have shown that thermosetting polymers such as epoxy, which have crosslinked covalent bonds, can also be electrospun. The resulting fibers have diameters ranging from 150 nm to 6 μm. Tensile mechanical properties of fibers with diameters varying between 410 nm and 4 μm are compared with those of molded epoxy bulk. The electrospun fibers exhibit approximately 555% higher strength, 300% greater stiffness, and a strain of about 109% compared to the equivalent properties of bulk epoxy. When compared with brittle molded bulk, these fibers showed ductile properties. We also observed a correlation between the fiber diameter and the mechanical properties. The molecular morphology of the fibers was monitored and analyzed using polarized micro-Raman spectroscopy to detect molecular orientation. A comparison with epoxy fibers of different diameters from previous studies was conducted to better understand the size effect. This study shows, explains and models the evolution of epoxy molecular morphology from the solution (soft matter) to fiber (solid-state), explaining the transition from brittle to ductile in epoxy fibers, and clarifying the molecular mechanisms that lead to improved mechanical properties.

Polyimide (PI) fiber is a promising and high-performance polymer fiber with high temperature resistance and low density; however, much energy is needed during the thermal imidization process. Here, PI fiber with excellent mechanical properties and high-temperature resistance was fabricated via the dry-jet wet spinning method for polyamic acid (PAA) precursor fiber, followed by stretching and thermal imidization reaction at a lower temperature. With the increase of the stretching ratio, the mechanical properties of the PI fiber increase significantly. When the stretching was twice as long, the tensile strength and initial modulus of the fiber were as high as 6.23 and 114.13 cN·dtex^–1, respectively. Fourier transform infrared results revealed that all samples were completely imidized at 260 °C. The resulting PI fibers exhibit only 5% weight loss at 539.53 °C, and its limiting oxygen index (LOI) can reach up to 32.6%, showing excellent high temperature resistance and flame-retardant properties as well as commendable mechanical performance, which compare favorably with those of other imidization methods.

The environmental and ecological concerns drive researchers to synthesize functional materials using components from natural resources. Nanocellulose (NC), derived from plants, marine animals, or microorganisms, is a green material attracting attention due to its abundance, biocompatibility, and biodegradability. NC’s interstice properties enable the synthesis of functional nanocomposites in forms like aerogels, foams, paper, sheets, or hollow filaments. This review briefly describes NC classification and production while comprehensively presenting its mechanical, rheological, optical, and electrical properties, offering foundational knowledge for future research. Additionally, it highlights recent developments in NC-based products across fields such as papermaking, water treatment, civil engineering, electronics, cosmetics, food, and medicine. For the first time, this paper explores recent advances in NC molecular simulation, providing insights into structure, arrangement, and interactions through molecular dynamic simulation. Finally, future prospects for NC-based applications are discussed to encourage studies addressing current challenges.