Solvent-Free Synthesis Creates High-Performance Polyester Nanocomposites

Polyethylene terephthalate (PET) has established itself as a fundamental material within the modern plastics industry, celebrated for its exceptional versatility and robust mechanical properties, underpinning critical sectors from packaging to construction. While advances in polyester molecular design using organic monomers have expanded its utility, the escalating demand for sophisticated materials in optical and electronic applications necessitates the exploration of highly precise, advanced processing techniques. Incorporating inorganic components into polymer matrices has long been a strategy to enhance physical characteristics across diverse applications. Conventional processing methods, such as melt extrusion, typically involve sequential steps including polymer synthesis, nanofiller modification, and compounding. However, conventional processing methods face limitations, including significant energy consumption, and strategies involving organic solvents face challenges related to their utilization, removal, and recovery. Residual solvents pose risks by impairing interfacial bonding and altering phase morphology, creating a conflict between achieving high consumer performance and meeting environmental mandates for benign manufacturing.

To overcome these inherent limitations, researchers have increasingly turned to advanced techniques like solution blending and in-situ polymerization, aiming to exploit intricate dynamic interactions at the nanoscale. A key focus in this field is developing green and sustainable approaches to tailor interfacial interactions at the nano and molecular levels within polymer nanocomposites. This research introduces a novel, solvent-free, one-step dual in-situ strategy for synthesizing polyethylene terephthalate (PET) nanocomposites incorporating 0.2 wt% of an inorganic component. This innovative method leverages the development of a barium borate ester (BBE) precursor, which is soluble in ethylene glycol (EG), one of the primary polyester monomers. By utilizing the high-temperature and high-pressure conditions characteristic of polyester polycondensation, which effectively establishes an inorganic solvothermal environment, the in-situ growth of the inorganic precursor is achieved.

This dual in-situ strategy simultaneously integrates PET polymerization, inorganic component growth under solvothermal conditions, and their molecular hybridization within a single reaction system. This eliminates conventional multi-step processes—such as surface modification of fillers, separate polymerization, and compounding—thereby achieving substantial energy conservation and emission reduction. Furthermore, this approach directly addresses the critical challenges associated with solvent utilization, removal, and recovery for molecular-level interfacial engineering. The resulting method offers a highly sustainable fabricating route for enhancing the physical properties of polymer nanocomposites.

Initial characterization of the precursor system demonstrated the transformation of the inorganic monomer BBE into its inorganic component. Analysis of the EG/BBE solution showed Tyndall scattering, suggesting the presence of BBE as colloidal particles dispersed within EG, particularly at higher concentrations. This weak scattering implies that, under the conditions of the dual in-situ synthesis, BBE interacts with EG primarily at the molecular level rather than forming large colloidal aggregates. This molecular-level interaction is consistent with the electrical conductivity observed in the solution, which shares characteristics typical of colloidal systems. Furthermore, X-ray diffraction (XRD) analysis confirmed that following the synthesis, the inorganic monomer BBE undergoes transformation into crystalline inorganic phases, evidenced by the emergence of distinct diffraction peaks, although these peaks were initially undetectable in the final nanocomposite due to the extremely low filling percentage.

The influence of the in-situ growth of the inorganic component on the PET polymerization process was assessed by examining intrinsic viscosity and end carboxyl group content, which showed negligible differences between neat PET and the resulting nanocomposite. This confirms that the dual in-situ synthesis process does not compromise polymer chain propagation or introduce side reactions, suggesting that incorporating a low filling of inorganic component exerts minimal influence on PET polymerization kinetics. However, despite these structural stability results, the chain conformation within the nanocomposite underwent significant alteration. Molecular fluorescence spectroscopy and Fourier-transform infrared (FT-IR) spectra revealed subtle differences between the neat PET and the nanocomposite. Materials Studio simulations provided further insight, demonstrating that the boron atom within the inorganic component approaches the ether oxygen atom of the polymer chains. The intermolecular distance between the organic and inorganic phases in the hybridized nanocomposite (3.718 Å) was significantly lower than in the counterpart nanocomposite (4.589 Å), a behavior attributed to the electron-deficient nature of boron acting as a Lewis acid, selectively interacting with electron-rich oxygen atoms in the polyester chains.

These molecular interactions have profound effects on the physical properties of the material. The incorporation of the inorganic component, even at extremely low fillings, notably influences the motion of polyester chains. Differential Scanning Calorimetry (DSC) curves showed that the nanocomposite exhibits a higher glass-transition temperature (Tg) compared to neat PET. This is attributed to the hybrid interfaces acting as physical entanglements, effectively restricting chain motion. Moreover, the inorganic component functions as a nucleating agent, promoting crystallization and facilitating the formation of more perfect crystals at high temperatures. Consequently, the nanocomposite features a higher melting crystallization temperature (Tc), a higher melting temperature (Tm), a lower cold crystallization temperature (Tcc), and a higher overall degree of crystallinity.

Morphological analysis using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the successful incorporation and dispersion of the inorganic phase. Although the low filling percentage made direct observation of shape and size difficult via SEM, energy-dispersive X-ray spectroscopy (EDS) mapping confirmed the uniform dispersion of all four constituent elements: boron, carbon, oxygen, and barium. TEM images revealed a well-defined normal distribution pattern with particle sizes primarily ranging from 1 to 5 nanometers, indicating precise control over particle size during the synthesis. Critically, the interfacial region was not simply categorized as neat PET or the inorganic component, but rather as significant interfacial domains featuring molecular-scale organic-inorganic hybridization, or hybrid interfaces.

The superior material characteristics of the nanocomposite were further quantified through mechanical and dielectric testing. Compared to neat PET, the nanocomposite demonstrated significant enhancements in mechanical performance, including a 30% increase in tensile strength, a 75% increase in elongation at break, and an 18% increase in impact strength. These improvements result from the hybrid interfaces acting as stress-dissipating networks, entangling numerous polymer chains and creating pathways for stress-induced unthreading during fracture. Furthermore, the nanocomposite exhibited significantly superior overall dielectric properties. At 1 kHz, the nanocomposite achieved a dielectric constant of 5.95, roughly twice that of neat PET. Simultaneously, the nanocomposite showed a much lower dielectric loss and leakage current. The breakdown strength increased from 582.6 MV/m for neat PET to 617.1 MV/m for the nanocomposite. These combined characteristics result in a superior energy-storage density, with the nanocomposite reaching an energy density of 15.03 J/cm³ at 650 MV/m, which is approximately 2.5 times that of neat PET film.

Subject of Research: Development of sustainable, solvent-free synthesis for high-performance polyester nanocomposites.

Article Title: Scalable high-performance polyester nanocomposites via solvent-free one-step dual in-situ synthesis

Article References: Sun, N., Zhang, M.-M., Liang, Q.-Q., Li, J.-L., Li, Y.-T., Jiang, Y., Zhou, K., & Zhang, Q.-P. (2026). Scalable high-performance polyester nanocomposites via solvent-free one-step dual in-situ synthesis. Results in Engineering, 32, Article 113585. https://doi.org/10.1016/j.rineng.2026.113585

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113585

Keywords: Polyester Nanocomposites, Sustainable Chemistry, Solvent-Free Synthesis, Polyethylene Terephthalate, Dielectric Properties, Mechanical Strength, In-situ Polymerization, Green Engineering, Scalable, high-performance, polyester, nanocomposites