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Abstract <p>The physicochemical principles of the bromination of ultra-high molecular weight polyethylene (UHMWPE) have been investigated. The conditions and regimes for conducting the process have been substantiated, and the kinetic characteristics of the process have been studied. Possible mechanisms of the UHMWPE bromination reaction have been considered. The experimental data from the UHMWPE bromination process were characterized using known kinetic models. The kinetic constants of the equations describing the bromination process were calculated. It was established that the Elovich model most adequately describes the process under study. It has been proposed that the bromination of UHMWPE is a three-stage process. In the first stage, molecular bromine migrates from the solvent medium to accessible adsorption centers. The second stage involves chemisorption. The final stage is the direct free-radical bromination. It was found that the conditions of the chosen technology allow for the production of brominated UHMWPE (B-UHMWPE) containing from 10 to 46 wt % bromine. It was shown that partial polymer degradation occurs during the process, resulting in a decrease of the initial polymer molecular weight by approximately 2.54 times. The IR spectra of brominated UHMWPE, alongside absorption bands for methyl and methylene group vibrations, contain absorption bands for C–Br bond vibrations (absorption maxima at 540, 614 cm<sup>–1</sup>). Scanning electron microscopy revealed that the supramolecular structure of B-UHMWPE differs from that of UHMWPE, showing some densification of structural elements with a simultaneous increase in their size distribution. Energy-dispersive X-ray analysis confirmed the presence of bromine and its uniform distribution throughout the UHMWPE volume. X-ray photoelectron spectroscopy (XPS) established that in the spectrum of the B-UHMWPE sample, besides the carbon line, peaks appear at 286.9 and 288.4 eV, corresponding to the (C–Br) bond. Also, in the Br3<i>d</i> region, a doublet is observed with a binding energy of the Br3<i>d</i><sub>5/2</sub> component equal to 70.5 eV, which is characteristic of bromine atoms covalently bonded to carbon atoms (Br–C). The mechanical characteristics of B-UHMWPE and a polymer composite material (PCM) based on UHMWPE with B-UHMWPE were investigated. It was found that the strength characteristics of B-UHMWPE are understandably inferior to those of the initial UHMWPE due to the decrease in molecular weight. The introduction of up to 9.5 wt % B-UHMWPE into the UHMWPE polymer matrix allows for an increase in the elastic modulus of the PCM by 1.4 times but does not lead to a statistically significant change in the elongation at break and tensile strength. Thus, B-UHMWPE can be used as a promising modifier for improving the deformation-strength parameters of UHMWPE-based composite materials.</p>

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Study of the Kinetics and Mechanism of the Bromination Reaction of Ultra-High Molecular Weight Polyethylene

  • 期刊论文

  • 发表日期：

    2025年6月1日

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  • R. V. Borisova,
  • A. M. Spiridonov,
  • T. A. Okhlopkova,
  • A. G. Alekseev,
  • S. N. Danilova,
  • V. P. Reshetnikov,
  • Yu. I. Borisov,
  • A. A. Okhlopkova

摘要

Abstract

The physicochemical principles of the bromination of ultra-high molecular weight polyethylene (UHMWPE) have been investigated. The conditions and regimes for conducting the process have been substantiated, and the kinetic characteristics of the process have been studied. Possible mechanisms of the UHMWPE bromination reaction have been considered. The experimental data from the UHMWPE bromination process were characterized using known kinetic models. The kinetic constants of the equations describing the bromination process were calculated. It was established that the Elovich model most adequately describes the process under study. It has been proposed that the bromination of UHMWPE is a three-stage process. In the first stage, molecular bromine migrates from the solvent medium to accessible adsorption centers. The second stage involves chemisorption. The final stage is the direct free-radical bromination. It was found that the conditions of the chosen technology allow for the production of brominated UHMWPE (B-UHMWPE) containing from 10 to 46 wt % bromine. It was shown that partial polymer degradation occurs during the process, resulting in a decrease of the initial polymer molecular weight by approximately 2.54 times. The IR spectra of brominated UHMWPE, alongside absorption bands for methyl and methylene group vibrations, contain absorption bands for C–Br bond vibrations (absorption maxima at 540, 614 cm–1). Scanning electron microscopy revealed that the supramolecular structure of B-UHMWPE differs from that of UHMWPE, showing some densification of structural elements with a simultaneous increase in their size distribution. Energy-dispersive X-ray analysis confirmed the presence of bromine and its uniform distribution throughout the UHMWPE volume. X-ray photoelectron spectroscopy (XPS) established that in the spectrum of the B-UHMWPE sample, besides the carbon line, peaks appear at 286.9 and 288.4 eV, corresponding to the (C–Br) bond. Also, in the Br3d region, a doublet is observed with a binding energy of the Br3d5/2 component equal to 70.5 eV, which is characteristic of bromine atoms covalently bonded to carbon atoms (Br–C). The mechanical characteristics of B-UHMWPE and a polymer composite material (PCM) based on UHMWPE with B-UHMWPE were investigated. It was found that the strength characteristics of B-UHMWPE are understandably inferior to those of the initial UHMWPE due to the decrease in molecular weight. The introduction of up to 9.5 wt % B-UHMWPE into the UHMWPE polymer matrix allows for an increase in the elastic modulus of the PCM by 1.4 times but does not lead to a statistically significant change in the elongation at break and tensile strength. Thus, B-UHMWPE can be used as a promising modifier for improving the deformation-strength parameters of UHMWPE-based composite materials.