Study Of Lignin On The Anti-aging Properties Of Polyolefin

Lignin is a kind of polymer, which is widely found in the cell wall of most land plants. Industrial lignin molecules contain multiple phenol structure, which can be used as antioxidant for polyolefin plastics. It can expand the application areas of industrial lignin and reduce the dependence on non renewable resources. It is full of great significance to realize the sustainable development of resources. The application of lignin and polyolefin plastic resin blend has been widely studied at present. However, the research on lignin as a functional additive for plastics has been rarely reported. In view of this, this paper attempts to use lignin as polyolefin plastics antioxidant and study the effect of the antioxidant properties of polyolefin plastics. This paper is devoted to exploring ways to improve the anti-aging performance of lignin and promoting the application of lignin in the plastic industry.In this study, different kinds of lignin were mixed with LDPE. The effects of Shuntai pine wood alkali lignin(SPAL), Xiangjiang pine wood alkali lignin(XPAL), Quanlin wheat alkali lignin(WAL) and Shengquan enzymatic hydrolysis lignin(SEHL) on the anti-aging performance of LDPE were studied. SPAL had the best protective effect on LDPE in thermal oxidative aging and UV aging. The conservation rate of the samples with 1% lignin after aging were up to 69.74% and 87.23% respectively. The efficiency of lignin absorption UV light had a positive correlation with its anti UV effect. The absorption efficiency of SPAL and XPAL on UV light were stronge, and its anti UV aging also had a better performance. In the high temperature environment, XPAL showed the best effect and the oxidation induction time(OIT) of XPAL has reached more than 7 minutes. The rheological test results showed that XPAL could sample storage modulus curve of "induction period", and the growth rate was relatively slow. It showed that XPAL had a better inhibitory effect on the aging of LDPE under high temperature environment. Therefore, high purity, high content of phenolic hydroxyl, low UV through the rate of pine wood(such as SPAL, xpal) was more suitable for polyolefin antioxidant.The different amounts of lignin were used to mix with different kinds of polyolefin materials and its anti-aging properties was studied. It showed that lignin could effectively improve the anti-UV aging properties of polyolefin materials, and had a small amplitude increase in anti thermalaging properties. In the UV aging environment, toughness of HDPE material with 2% lignin improved, and the conservation rate of fracture tensile rate reached 168% which was close to industrial light stabilizer. In the thermal oxidative aging environment, the conservation rate of fracture tensile rate of HDPE, LDPE and PP with 2% lignin reached 89.80%, 53.91% and 67.80% respectively. In the high temperature aging environment, adding 1% lignin could make the OIT of HDPE up to 22.4 minutes. But for LDPE and PP, it needed to add 3% lignin in order to make the oxidation induction period up to 15 minutes or more. Rheological test showed that lignin could reduce the aging rate of polyolefin in the high temperature condition. The anti-aging performance was still poor compared to industrial antioxidant 1010. Aiming at the disadvantages of lignin in the thermal aging condition of polyolefin protection ability insufficient, this paper discussed several methods to improve the lignin thermal aging properties.1% aluminum stearate, stearic acid, KH-570, MA-PE were used to improve lignin dispersion effect in LDPE and improve the anti-aging effect. Appearance observation and SEM observation showed that the effect of stearic acid was the best. Lignin distribution was uniform and no large particles were observed after adding 1% stearic acid. Increasing lignin dispersion could indirectly improve the ability of free radicals capture, and extend the OIT of LDPE. The OIT was 8.2 minutes after adding 1% stearic acid which increased by 1 minute compare to the control sample. At the same time, stearic acid and stearic acid aluminum could effectively increase the UV absorption ability of lignin. The UV transmittance dropped to 47.85% from 61.42% after adding 1% aluminum stearate.The different contents of antioxidant 1010 and lignin were compounded to improve the anti-aging effect of LDPE. The results showed that it was helpful to improve the anti-aging performance of lignin and 1010 antioxidant compound in LDPE. After adding 1% lignin and 0.1% antioxidant 1010, the LDPE conservation rate of fracture tensile rate reached 85.64%. Lignin and antioxidant 1010 compound could significantly improve the OIT of LDPE. The OIT of the sample which compounded 1% lignin and 0.05% antioxidant 1010 reached 36.5 minutes and it could meet the basic needs of industrial production.The mechanism of thermal aging resistance and UV resistance of lignin in polyolefin plastics were discussed. Phenolic compounds in lignin could capture free radicals and prevented the automatic oxidation cycle in polyolefin under the action of thermal oxygen. Lignin conjugated structure could absorb UV light, and played the role of UV shielding under the action of UV irradiation.The effects of lignin on anti-aging performance in polyolefin was studied in this paper. It found that the thermal aging resistance and UV resistance ablities in polyolefin could be improved by adding lignin. Lignin could be used as plastic antioxidant antioxidant. This research had important significance to solve the pulping black liquor pollution problems and to alleviate the problem of shortage of petrochemical resources. At the same time, it could broaden the application field of lignin in plastic industry.