The impact of degradation on plastics is a critical factor influencing their properties and behavior, particularly evident in polyethylene (PE) and polypropylene (PP) and their blends. However, the effect of photoaging and thermal degradation, specifically within recycled polyethylene (rPE) and recycled polypropylene (rPP), on the thermo-mechanical and thermostability aspects of these blends remains unexplored. To address this gap, a range of materials, including virgin polyethylene (vPE), recycled polyethylene (rPE), virgin polypropylene (vPP), recycled polypropylene (rPP), and their blends with different ratios, were comprehensively investigated. Through a systematic assessment encompassing variables such as melting flow index (MFI), functional groups, mechanical traits, crystallization behavior, microscopic morphology, and thermostability, it was found that thermo-oxidative degradation generated hydroxyl and carboxyl functional groups in rPE and rPP. Optimal mechanical properties were achieved with a 6:4 mass ratio of rPE to rPP, as validated by FTIR spectroscopy and microscopic morphology. By establishing the chemical model, the changes in the system with an rPE–rPP ratio of 6:4 and 8:2 were monitored by the molecular simulation method. When the rPE–rPP ratio was 6:4, the system’s energy was lower, and the number of hydrogen bonds was higher, which also confirmed the above experimental results. Differential scanning calorimetry revealed an increased crystallization temperature in rPE, a reduced crystallization peak area in rPP, and a diminished crystallization capacity in rPE/rPP blends, with rPP exerting a pronounced influence. This study plays a pivotal role in enhancing recycling efficiency and reducing production costs for waste plastics, especially rPE and rPP—the primary components of plastic waste. By uncovering insights into the degradation effects and material behaviors, our research offers practical pathways for more sustainable waste management. This approach facilitates the optimal utilization of the respective performance characteristics of rPE and rPP, enabling the development of highly cost-effective rPE/rPP blend materials and promoting the efficient reuse of waste materials.

Recycled polyethylene (r‐PE) is a promising recycled polymer modifier for asphalt, yet its inherent non‐polar property leads to poor interfacial compatibility with asphalt matrix, triggering phase separation, particle agglomeration and degraded low‐temperature cracking resistance. In this work, waste high‐density polyethylene plastic bottles were adopted as raw material, and two functionalized r‐PE modifiers bearing ester (–COOR) and carboxyl (–COOH) groups were synthesized through melt‐grafting. Modified asphalt specimens with modifier dosages ranging from 1% to 5% were prepared by high‐speed shearing with 70# base asphalt. Conventional performance tests, storage stability evaluation, dynamic shear rheometer tests, Fourier transform infrared (FTIR) and SEM micro‐characterization were carried out. Combined with matrix‐based multiple regression and quantum‐chemical molecular simulation, this study quantitatively separated the weighting effects of functional‐group type and modifier dosage, and comparatively revealed the interfacial modification mechanisms. The results demonstrate that functionalization significantly enhances the interfacial interaction between r‐PE and asphalt, and r‐PE‐COOH achieves better overall performance. At the optimal dosage of 3% (under the experimental conditions of this study), r‐PE‐COOH‐modified asphalt has a 5 °C ductility of 32.0 cm, which is 18.5% higher than r‐PE‐COOR modified asphalt and 47.5% higher than unfunctionalized r‐PE modified asphalt. Within the dosage range of 1%–5%, r‐PE‐COOH‐modified asphalt maintains a softening‐point difference below 2.1 °C and exhibits superior rutting resistance according to rheological tests. Regression analysis identifies modifier dosage as the dominant factor governing rheological properties, whereas functional‐group type exerts a secondary influence. Microscopic and simulation results indicate that r‐PE‐COOH forms stable cross‐linked networks via esterification reaction with polar components in asphalt, while r‐PE‐COOR mainly interacts through physical adsorption. Both modifiers construct the dual ‘cross‐linked network‐particle anchoring’ structure to improve compatibility. This study provides theoretical support for the molecular design of sustainable recycled‐polymer asphalt modifiers.

Growing demand for pavement maintenance promotes reclaimed asphalt pavement (RAP) recycling, yet multi-scale comparative research on rejuvenators remains limited. This study compared a commercial bio-based Rejuvenator A and a petroleum-based Rejuvenator B to reveal how chemical compositions control asphalt regeneration. Following JTG 3410-2025 standards, asphalt binders underwent extended RTFOT aging (75, 112.5, and 150 min) and were externally blended with rejuvenators at 5%, 7.5%, and 10% by binder mass. A multi-scale framework combining macro tests, interfacial characterization, SARA fraction analysis, ATR-FTIR, and molecular dynamics (MD) simulations was established. Results indicated that the two rejuvenators acted via different mechanisms. Rejuvenator B contained 31.64% saturates and restored aged asphalt mainly through physical dilution and softening. This rejuvenator formed 0–80 hydrogen bonds dominated by weak C–H···O interactions, and the corresponding rejuvenated asphalt yielded a CII of 0.293. It was effective for 75 min-aged binders yet produced more oxidation products after re-aging. Conversely, Rejuvenator A, characterized by 68.10% aromatics and 20.17% resins, exhibited a 3–5° lower equilibrium contact angle, and a roughly 13% shorter relative penetration time than Rejuvenator B. Its network of 150–250 hydrogen bonds effectively disrupted asphaltene aggregates, reducing the CII to 0.180. Consequently, Rejuvenator A successfully restored 112.5 min- and 150 min-aged asphalt with significantly lower secondary oxidation. These performance differences were governed by aromatic and polar fractions rather than feedstock origins. While quantitative findings are sample-specific, the established framework provides theoretical references for engineering rejuvenator selection and high-performance regenerant design.