As a skeleton material, polyester (PET) fiber can significantly improve the strength and durability of rubber composites, but the interfacial adhesion between polyester fiber and rubber is poor due to the chemical inertia of PET fiber surface. Resorcinol-formaldehyde-latex (RFL) impregnating solution is usually used to treat PET fibers, but RFL contains toxic components such as resorcinol, which is harmful to the human body. A simple and less toxic resin-impregnating system cresol-formaldehyde-latex (CFL) was obtained by alternating resorcinol with low-toxicity cresol and m-cresol formaldehyde resin was synthesized from m-cresol and formaldehyde. CFL (m-cresol formaldehyde resin latex) systems with different C/F mole ratios and CF resin/latex ratios were adopted to modify the surface of PET fibers. The strip peeling adhesive and the H pull-out test results indicated that the PET fiber/rubber adhesion strength increased with the increase in the formaldehyde dosage and the CF resin content, and the peeling force value and the H-pull-out force of treated PET/rubber composites reached 7.3 N/piece and 56.8 N, respectively. The optimal choice of CFL adhesive system was obtained, when the C/F mole ratio was 1/2 and the CF resin/latex weight ratio was 0.23. This environment-friendly CFL dipping emulsion can be used as a new surface modification strategy as it can remarkably enhance the interfacial adhesion of PET/rubber composites.
Individual monitoring is of great significance in efforts to protect the health of radiation workers and improve the level of radiation protection and management. This paper presents a retrospective analysis of occupational exposure to ionizing radiation from medical practice in the region of Hohhot, China, from 2004 to 2020. Results show that the average annual effective dose of occupationally exposed workers in medical practice significantly declined from 1.44 mSv in 2005 to 0.29 mSv in 2020 (Z = −5.23, P < 0.05). The number of medical radiation workers increased by 181%, the composition of radiation workers whose average annual effective dose exceeded 1 mSv decreased, and the number of radiation workers whose average annual effective dose was less than or equal to the minimum detection level (MDL) increased yearly over the 17-y study period. It was found that the dose of 1.106 mSv received by workers in interventional radiology is significantly higher than the doses of 0.52 mSv in dental radiology, 0.47 mSv in radiotherapy, and 0.33 mSv in all other medical uses (Z = 3.71, 9.13, 5.93, respectively; P < 0.05). The distribution ratios of workers in nuclear medicine and interventional radiology whose annual individual effective dose exceeded 5 mSv were 0.040 and 0.043, respectively, which are significantly higher than those in other occupational categories (χ 2 = 307.11, P < 0.05). It was also shown that the average annual effective dose of 0.67 mSv in interventional radiology is significantly higher than that of 0.17 mSv in radiotherapy (Z = 3.39, P < 0.05) in 2020. According to these observations, the exposure of radiation workers in medical practice in Hohhot meets the requirements of the China standard. This study shows that the status of radiation workers in medical practice has obviously improved during the period 2004-2020. However, it is still necessary to focus on the protection of groups with high occupational exposure risk, and the continuous improvement of protection measures, monitoring means, and radiation workers' training, especially for the workers in the fields of interventional radiology and nuclear medicine.
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