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Quality R & D
Shi Xian Study 12 | Professor Ni Xiuyuan of Fudan University: The environment of UV curable epoxy materials is unstable? Try loading polyol into clay nanotubes
UV-curable epoxy materials are widely used in the fields of coatings, electronics industry, and 3D printing technology. However, high flammability is one of the major problems with materials. During the combustion process, the photoinitiator remaining in the UV curing material can generate active free radicals, which accelerates the combustion degradation process of the polymer. Intumescent flame retardants are often used for the flame retardancy of UV-cured epoxy materials, but the disadvantage is that the polyol as a carbon source is too absorbent and affects the mechanical properties of epoxy materials.
In response to this, Professor Ni Xiuyuan of Fudan University and his research team, Dr. Zhengcheng Cheng, used a method of loading polyol into clay nanotubes to effectively improve the hygroscopicity of the polyol and successfully prepare environmentally stable UV-curable epoxy materials.
Halloysite nanotubes (HNTs) have good compatibility in polar polymers and are often used as nanocarriers. HNT can form a network structure during the combustion process, which is conducive to the improvement of flame retardancy. In this study, the researchers first prepared a modified halloysite tube (HNT-P) by vacuum adsorption, which replaced the air in the lumen of HNT with pentaerythritol (PER) solution by sonication and loaded HNT with PER . APP and HNT-P are then added to the UV curable epoxy resin (EP) in different ratios. A homogeneous mixture, namely an EP / HNT-P composite, is prepared by continuous stirring. In addition, the researchers also prepared EP / HNT / PER composites by adding PER and HNT in the usual way; in order to facilitate the later stage of HNT-P composites and HNT and PER directly added to the composite's moisture resistance.
Researchers test and analyze the combustion properties and hygroscopicity of composite materials:
The composition and LOI test results of pure EP, EP / HNT-P and EP / HNT / PER composite materials are listed in Table III. The LOI value of pure EP is only 18, which has high flammability; APP / HNT-P (EP / HNT-P) UV curable epoxy resin. With the increase of APP / HNT-P, the LOI value increases significantly. With 35wt% APP / HNT-P added, the LOI value of EP / HNT-P can reach 28.2. The simple blend of EP / HNT / PER composites has a LOI of only about 20. The results show that the two components in HNT-P have a good synergistic flame retardant effect.
In addition, the CC test results show that compared to pure EP, the TTI of 25% by weight of EP2 increased from 24s to 33s, and the pHRR and THR decreased from 1002.4 kM / m2 and 104.1 MJ / m2 to 562 kM / m2 and 51.8 MJ, respectively. / m2, showing lower flammability. APP / HNT-P may have the following reactions during the combustion process, leading to the improvement of combustion performance.
The maximum hygroscopicity (Mmax-m) of the test material characterizes the hygroscopicity of the material (Figure 5). Compared with EP / HNT / PER, the Mmax-m of EP / HNT-P decreases from 2.08wt% to 0.87wt at 40 ° C. %, A decrease of 58.2%. When the temperature was raised to 85 ° C, it decreased from 5.68 wt% to 2.90 wt%, a decrease of 48.9%. In addition, the water absorption (Figure 6) test at 85 ° C, the maximum water absorption (Mmax-w) decreased from 7.83 wt% of EP / HNT / PER to 6.42 wt% of EP / HNT-P. The results show that EP / HNT-P composites have better moisture resistance and water resistance than EP / HNT / PER composites.
Finally, the researchers tested the storage modulus of EP / HNT / PER and EP / HNT-P by adding DMA to the two composite materials. The former softens the resin due to the hydrophilic nature of the PER, and the latter has been loaded to the latter due to the hydrophilic PER. In HNT, the softening effect is reduced. The results show that the use of HNT-P can effectively inhibit the water absorption of PER.
Overall, this study of loading PER with HNT and synergistically modifying the flame retardancy and water resistance of UV-cured epoxy resins with APP has been very successful. By mounting PER in hollow nanotubes to form a new structure, the problems of moisture sensitivity and the like of polyols were effectively alleviated.