Use of recycled product is important as it conserves natural resources and energy, reduces waste and pollution, and helps combat climate change. Now, the textile industry is seeking for sustainable alternatives to virgin polyester, understanding the quality and limitations of recycled fibers becomes essential. This study investigates the comparative performance of virgin and recycled polyethylene terephthalate (PET) fibers in order to enable the substitution of virgin polyester. The primary objective was to evaluate how recycling affects fiber structure and performance by evaluating single-fiber characteristics. Recycled PET fibers exhibited about 26% reduction in tensile tenacity compared to virgin fibers, but showed higher elongation at break and greater crimp stability. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that both the fibers retained identical chemical structure suggesting minimal chemical degradation. However, SEM imaging revealed that recycled fibers had rougher surfaces, increased diameter (~15.7 μm vs. ~14.7 μm), and visible surface defects, likely due to thermo-mechanical damage. These structural changes contribute to the lower yarn strength, higher nep formation, and processing difficulties observed in textile mills utilizing 100% recycled PET.

Poly(propylene carbonate) (PPC) is synthesized through the alternating copolymerization of propylene oxide (PO) and carbon dioxide (CO₂) and has been widely studied as a sustainable polymer material. Although PPC is known for its biodegradability, biocompatibility, high optical transparency, and gas-barrier property, its relatively low thermal stability and limited mechanical strength restrict its broader practical applications. To address these limitations, we designed a graft copolymer that integrates PPC with a mechanically robust and biodegradable backbone. Cellulose acetate (CA), a high-performance thermoplastic widely utilized in fiber and film applications, was employed as the backbone, and PPC segments were covalently introduced as side chains to construct CA-graft-PPC. The designed CA-graft-PPC was synthesized by the “grafting-from” strategy, in which the PO/CO₂ alternating copolymerization was conducted using CA as a macro-chain transfer agent. The molecular weight of the PPC side chains and the grafting density were systematically tuned by adjusting the monomer feed ratio and the degree of substitution of CA. Thermogravimetric analysis revealed a two-step degradation behavior corresponding to the PPC side chains and the CA backbone. Compared with neat PPC, CA-graft-PPC exhibited enhanced thermal stability. Tensile tests of PPC/CA-graft-PPC blend films demonstrated a slight improvement in tensile strength. The reinforcement effect depended strongly on the grafting density and side-chain length, reflecting the balance between chain entanglement and interfacial interactions.

Three-dimensional fibrous networks combine high porosity with a characteristic nonlinear J-shaped compressive response, yet the topological origins of this stiffening behavior remain elusive due to the complexity of their random architecture. Here we investigate the structural mechanism governing this response by integrating persistent homology (PH) analysis of X-ray computed tomography images with image-based finite element modeling. We demonstrate that persistent homology efficiently identifies fiber contact points and Side-by-side fused regions from tomographic images, enabling construction of a topology-faithful finite element model that successfully reproduces the J-shaped compressive response. Beyond structural identification, the resulting PH1 loop diameter distribution serves as a phenomenological descriptor of the underlying heterogeneity, qualitatively accounting for the sequential stiffness transition from large, compliant loops to small, stiff ones as compression progresses. This mechanism is corroborated by scaling analysis of the nominal stress-volume fraction relation, which reveals a structural evolution from an initial geometric contact regime (S ∝ϕ³) to a stable bending-dominated regime (S ∝ϕ²). Our findings suggest a topological framework for relating microscopic constraint networks to macroscopic mechanics, providing fundamental design principles for advanced disordered materials.