| Films are one of the important agricultural production materials in China.However,the problem of residual film pollution caused by the mass use of traditional polyethylene(PE)films is becoming more and more serious.It is necessary to develop and apply biodegradable films.Poly-(butylene adipate-co-terephthalate)(PBAT)has excellent film-forming properties and has become the mainstream material for preparing biodegradable films.However,the water vapor barrier property of PBAT film is poor,which limits its application in agriculture.So it is necessary to improve the water vapor barrier property of PBAT films.In this study,the nano-fillers composite method and the polymers blending method are selected to improve the water vapor barrier property of PBAT film,starting with mica and polypropylene carbonate(PPC)for modification,and using ethylene-vinyl acetate copolymer wax(EVA wax)to solve the problem of mica’s poor dispersion in PBAT.Two kinds of modified biodegradable films were prepared:PBAT/EVA-mica composite films and PBAT/PPC blend films.What’s more,field application evaluation experiments of dwarf kidney bean were carried out on the two kinds of modified biodegradable films.The results are as follows:(1)The addition of modified mica,EVA-mica,could enhance water vapor barrier properties,mechanical properties,and anti-aging properties of PBAT films.Compared with the EVA-mica with other sizes,the EVA-mica with 1250 mesh had the best modification effect on PBAT films.When the content of EVA-mica with 1250 mesh was 2%,the water vapor barrier property of PBAT/EVA-mica films was the best,and this film was numbered M2-2.The water vapor permeability of the M2-2 film was 119.87 g/(m~2·24h),which was 80.09%lower than that of PBAT films.The tensile load and tear load of the M2-2 film were 20.00 N and 5.10 N,respectively.They were 26.82%and 2.24%higher than those of PBAT films respectively.The water vapor permeability,tensile load and tear load of the M2-2film after 100 hours of aging were 72.96%,34.51%,and 6.75%higher than those of PBAT films,respectively.EVA-mica was in the form of a single-layer sheet,and the surface was covered with EVA wax.The thermal stability of EVA-mica could meet the requirement of film production.The dispersibility of EVA-mica in the PBAT was??better than that of mica,which could form more uniform water barrier layers.At the same time,EVA-mica could play a role in heterogeneous nucleation to promote crystallization,increase the proportion of crystalline areas with better water barrier properties,and enhance the water vapor barrier property of PBAT/EVA-mica films.Compared with PBAT films,the crystallite size of PBAT/EVA-mica film was increased by 156.93%,and the crystallinity was increased by 20.22%.(2)When the content of PPC was 10%,the comprehensive properties of PBAT/PPC films were good,and this film was numbered P2.The water vapor permeability of the P2 film was 386.31g/(m~2·24h),which was 35.85%lower than that of PBAT films.The tensile load of the P2 film was11.85 N,and the tear load was 3.55 N.The water vapor barrier property and tear load of the P2 film after 100 hours of aging were 47.88%and 21.33%higher than those of PBAT films,respectively.PPC was distributed in a spherical phase in PBAT/PPC films,which could extend the diffusion path of water vapor in films.At the same time,PPC and PBAT were not completely compatible,and PPC could play a role of heterogeneous nucleation to promote crystallization,improve the crystallization area with good water resistance,and further improve the water vapor barrier property of PBAT/PPC films.When the content of PPC was 10%,the crystallinity of PBAT/PPC films was the highest,and this film was the P2film.The crystallinity of the P2 film was 15.88%higher than that of PBAT films.The crystallite size of the P2 film was 97.45%higher than that of PBAT films.(3)In the field application evaluation test of dwarf kidney bean,the degradation rate of the M2-2film and the P2 film was slower than that of PBAT films.The start degradation data of the M2-2 film and the P2 film were 10 days later and 15 days later than that of PBAT films in the field,respectively.The data when the M2-2 film and the P2 film reached level 2 degradation were 5 days later and 20 days later than that of PBAT films in the field,respectively.The water vapor barrier property and the mechanical property of the M2-2 film and the P2 film in the field degradation process were always better than those of PBAT films,and the reduction of mechanical properties of the M2-2 film and the P2film in the field was smaller than that of PBAT films.The water vapor barrier property of the M2-2 film and the P2 film in the later stage of the field demolition was 35.08%and 42.42%higher than that of PBAT films,and their mechanical properties were 77.38%and 30.16%higher than that of PBAT films,respectively.The mechanical properties of PBAT films,the M2-2 film and the P2 film were decreased by 69.10%,47.91%,and 63.76%,respectively.Compared with PBAT films,the seedling period of dwarf kidney bean covered with the M2-2 film and the P2 films was 2 days earlier,and the vine period was 9 days earlier.After 75 days in the field,the plant height of dwarf kidney beans covered with the M2-2 film and the P2 film was 6.13%and 9.08%higher than that with PBAT films,respectively.The weight of single pod of dwarf kidney bean covered with the M2-2 film and the P2 film was 5.65%and6.11%higher than that of PBAT films,and the number of pods per plant was both 8.11%higher than that with PBAT films,respectively.The yield of dwarf kidney bean covered with the M2-2 film and the P2 film was 10.57%and 11.43%higher than that with PBAT films,respectively.Compared with PBAT films,the M2-2 film and the P2 film could better promote the growth and development of dwarf kidney bean,speed up its growth period,and significantly increase the yield of dwarf kidney bean.In conclusion,two modified biodegradable films with good water vapor barrier properties,PBAT/2%-1250 mesh-EVA-mica films and PBAT/10%-PPC films,were prepared and screened by nano-filler composite method and polymer blending method in this study.The water vapor barrier properties of these two modified films were 80.09%and 35.85%higher than that of PBAT films respectively.The adding of EVA-mica and PPC separately could increase the hydrophobic layer in the middle layer,and play a role of heterogeneous nucleation to increase the crystallinity of PBAT,thereby reducing the water vapor transmission rate of the PBAT mulching film.This study clarified that the two modified biodegradable films could promote the growth and development of the dwarf kidney bean and significantly increase its yield in field applications. |
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