Lignin-reinforced Functionality Of Biomass Based Liquid Mulching Film

In modern agriculture,polyethylene mulch film was used to keep soil temperature and humidity stable,control weeds and pests,so as to increase the yield and quality of crops.However,the unreasonable disposal of plastic mulch film has caused environmental problems such as soil pollution and soil degradation.As a substitute for polyethylene mulch film,eco-friendly biomass liquid mulching film has received more and more attention.Biomass liquid mulching film is a kind of spray-able mulching film which formed by special processing of natural polymer such as crop straw,animal and plant collagen.Compared with traditional polyethylene mulch film,biomass based liquid mulching film show poor barrier property and function,which limits its application in agricultural production.To solve this problem,lignin with high reactivity,anti-UV and anti-oxidation properties was selected as the reinforcing agent to biomass liquid mulching film.In this study,two typical industrial lignin were selected to enhance the barrier properties,heat preservation and weed control function of biomass liquid mulching film by adopting structure design or chemical crosslinking strategy,respectively.（1）Firstly,focusing on the problem of poor barrier properties of biomass liquid mulching film,industrial dealkaline lignin was selected to improve the barrier performance of liquid mulching film.However,the poor water solubility of industrial dealkaline lignin limited its application in liquid mulching film.Therefore,a facile cyanoethylation technique route was proposed to improve the water-solubility of industrial dealkaline lignin.Inspired by the mussel layered structure,the obtained cyanoethyl lignin（CEL）was used as biomimetic binder to couple with cellulose nanowhiskers（CNW）and form CEL@CNW building block.Then CEL@CNW building block was mixed with water-soluble polymer polyvinyl alcohol（PVA）to fabricated liquid mulching film with oxygen and UV barrier properties.It was shown that cyanoethyl group can replace a small part of phenolic hydroxyl group in lignin,and improve the water solubility of lignin by destroying the strong hydrogen bond of lignin,while remaining its UV barrier property and antioxidant activity.In addition to acting as functional additive,it was proposed that the CEL incorporation mediated the layered structure of liquid mulching film thus significantly enhancing its overall barrier performance.The PVA/CEL@CNW liquid mulching film showed excellent UV barrier（reached ⁰% transmittance at 200 nm with 10 wt% of CEL@CNW）and oxygen barrier ability(oxygen transmission rate reached ⁰.12 cm³ m^-2d^-1kPa^-1 with 5 wt% of CEL@CNW),so it could be used for the protection of photosensitive avermectin pesticide against photo-degradation.The application potential of the fabricated PVA/CEL@CNW liquid mulching film was verified through the good soil water resistance property and the facilitation of corn seed germination and seedling growth.This work provided a new strategy to valorize industrial waste lignin through water-soluble lignin pursuing,while tailoring a technique platform for the fabrication and application of barrier liquid mulching film toward a more sustainable agriculture.（2）As for the poor heat preservation and weed control function of biomass liquid mulching film,lignin-containing cellulose nanofiber（LCNF）from biomass refining industry was selected and modified to strengthen the heat preservation and weed control function of biomass liquid mulching film.Among them,LCNF was prepared by DES pretreatment coupled sanding nanocellulost technology,and Fe₃O₄ nanoparticles were loaded in situ to construct structural units with photothermal conversion function,which could be used to enhance the heat preservation and weed control function of gelatin based liquid mulching film.The results showed that the residual lignin in LCNF had a small negative effect on the crystallinity and water retention properties of LCNF,but it did not restrict the cellulose nanofibrillates.Moreover,the phenol hydroxyl group in the residual lignin enhanced the reactivity of LCNF,which was conducive to the loading of Fe₃O₄ on LCNF.The obtained LCNF@Fe₃O₄ was an ideal material for the preparation of functional liquid mulching film.The Gel/LCNF@Fe₃O₄ composite film designed with chemical crosslink strategy has excellent mechanical and barrier properties.LCNF@Fe₃O₄ was used as functional building block with photo-shielding and photothermal conversion performance,play an important role in reducing the light transmittance and improving the photothermal conversion effect of liquid mulching film.The Gel/LCNF@Fe₃O₄ liquid mulching film can effectively inhibit the germination of weed seeds and promote the growth of maize seedlings,which were expected to be applied in agricultural production as thermal insulation and weeding mulch film.