Specific Ion Effects on the Enzymatic Degradation of Polyester Films

Soil environment on earth contains a variety of ions,which are expected to play a vital role in the biodegradation of plastics discarded in the environment.In this work,poly(butyleneadipate-co-terephthalate)(PBAT)is employed as a model biodegradable plastic to study the specific ion effects on the enzymatic degradation of polyester plastics.The results show that the specific ion effects on the enzymatic degradation rate of the PBAT films and on the catalytic rate constant for the enzymatic hydrolysis of the ester bonds are strongly dependent on temperature and ionic strength.Both the enzymatic degradation rate and catalytic rate constant decrease following the trends Na^(+)>K^(+)>Ca^(2+)and Cl^(-)>SO_(4)^(2-)>NO_(3)^(-)for cations and anions,respectively,indicating that the ion-specific enzymatic degradation of the PBAT films is closely correlated with the specific ion effects on enzymatic hydrolysis of the ester bonds.Our study shows that the specific ion effects on the enzyme activity can be understood by taking into account the ion-specific cation-anion interaction,ionic dispersion force,salting-out effect and salting-in effect.This study of specific ion effects on the enzymatic hydrolysis of the ester bonds and the resultant enzymatic degradation of the PBAT films would offer us a new clue to develop new biodegradable,environmentally friendly synthetic plastics.

Effects of biodegradable mulching films on soil hydrothermal conditions and yield of drip-irrigated cotton(Gossypium hirsutum L.)

The pollution of cotton fields by residual films is serious on ground that has been subjected to long-term drip irrigation in Xinjiang,China,and biodegradable mulches are therefore advocated as an alternative to plastic ones.In this study the mulching with biodegradable films under drip irrigation conditions in the extremely arid region of Xinjiang was investigated to determine the effects on soil hydrothermal conditions and cotton(Gossypium hirsutum L.)yield over two consecutive years(2019-2020)using plastic mulch made from polyethylene(PE)film and four types of biodegradable films,including black opaque oxidation-biodegradable film(M1),colorless transparent oxidation-biodegradable film(M2),black opaque fully biodegradable film(M3)and white translucent fully biodegradable film(M4),which had different levels of biodegradability(i.e.different degradation times and rates).The biodegradability,soil water contents,soil temperatures and cotton yields were compared between the degradable(M1 to M4)and PE films.The results indicated that M2 was degraded the quickest and showed the highest degree of degradation compared with the other degradable films and PE films.The degradation rates of the various mulching films were ranked in a descending order as M2,M4,M1,M3 and PE,but the PE mulch exhibited the best performance in terms of soil water and heat conservation throughout the growth period.The soil heat preservation and moisture conservation performance under biodegradable films mulching at the cotton seedling stage and budding stage was similar to that of PE film.The average soil temperature at a depth of 5 cm under mulching with the degradable films was 2.66°C-5.06°C(p<0.05)lower than that under traditional PE films at the flowering stage.At the late stage of cotton growth,the water content of shallow soil mulched with PE film was better for plant grown than that under the biodegradable films.The effect of film degradation on the shallow soil water content was much greater than that in deep soil,especially at a depth of 0-40 cm.However,in all treatments,the seedling rate and growth index of cotton under M2 were equivalent to that found under the PE film.Moreover,the cotton yield using M2 was slightly higher than that for the PE film.Compared with the PE film,the yield of cotton mulched with M1,M3 and M4 was decreased by 7.50%,6.45%and 2.83%in 2019,and 9.82%,6.48%,and 2.13%,in 2020,respectively.Therefore,based on the performance in improving cotton yield and maintaining soil moisture,the biodegradable transparent film(M2)with an 80 d induction period is recommended as a competitive alternative to plastic mulch to enhance crop yield and control soil pollution.

Degradability of biodegradable plastic films and its mulching effects on soil temperature and maize yield in northeastern China

Plastic film is an important resource in agricultural production,but it takes hundreds of years to degrade completely in natural environment.The large-scale use of plastic film will inevitably lead to serious environmental pollution.One way to solve the problem is to develop a substitutable mulching film,such as a biodegradable film that can ultimately be decomposed to water,carbon dioxide,and soil organic matter by micro-organisms.In this study,a 2-year experiment was conducted to determine the degradation properties of a biodegradable plastic film,including degradation rate,surface microstructure,tensile strength and elongation at break,and the effects of different mulching treatments on soil temperature and maize yield.The mulching experiment was conducted with three different biodegradable plastic films with different degradation rates,using a common plastic film and a non-mulched treatment as control.With the addition of the additives for degradation in the biodegradable plastic films,the degradation rates increased significantly,which were 7.2%-17.8%in 2017 and 18.1%-35.2%in 2018 after maize harvesting.However,the degradation occurred mainly on the ridge side.The decrease in tensile strength and elongation was proportional to the degradation rate of the degradable film.The SEM results indicated that the surface microstructures of the biodegradable films were loose and heterogeneous after maize harvesting.Biodegradable plastic film mulching increased the soil temperature at soil depths of 5 cm,15 cm,and 25 cm,over the maize’s entire growth period,by 3.1℃-3.2℃ in 2017 and 1.2℃-2.1℃ in 2018 compared with the non-mulched treatment.The biodegradable plastic film increased the maize yield by 10.4%-14.3%in 2017 and 11.6%-24.7%in 2018.The soil temperature and maize yield increases were statistically significant;however,with respect to maize qualities,there were no statistically significant increases among the five treatments.This study shows that biodegradable plastic film can be used as a substitute for common plastic film.However,the ingredients in biodegradable plastic films should be improved further to ensure that they can be degraded completely after crop harvest.

Effects of degradable films with different degradation cycles on soil temperature,moisture and maize yield

Photo biodegradable film is an ideal degradable mulch film with synergistic effect of photo-degradability and biodegradability.To examine the covering effects of different films,maize was cultivated in the field with three kinds of degradable films(DF)mulching which had different degradation cycles(DF No.1,No.2 and No.3),with common plastic film mulching and no filming mulching(open ground)as comparison.The degradation rates and degrees of degradable films were examined,and the effects of different films on soil temperature,soil moisture,maize yield and relevant characteristics in each treatment were analyzed.The results indicated that the degradable films had good degradability,and the weight loss rate in 100 d for DF No.1,No.2,and No.3 were 22.31%,19.46%,and 15.63%,which were 4.16,3.63,and 2.92 times of the plastic film,respectively.In the early period of maize growth,the degradable films had good warming effects on soil,which were similar with the plastic film.The effect of DF No.2 on soil water conservation was slightly better than that of DF No.1 or No.3,similar with that of the plastic film.The soil water contents in 0-140 cm depths were significantly higher for DF No.2 than that for the open ground(p<0.05).The degradable films could significantly promote the ear development of maize,improve the ear characteristics,shorten the bald tip,and increase kernel number per plant(KNP)and 1000-kernel weight(TKW).The grain yields(GYs)for DF No.2,No.1,and No.3 were significantly improved,with 35.15%,31.35%,and 30.07%higher than that the open ground respectively(p<0.05).With no significant difference between DF and the plastic film,the GY was increased more for DF No.2 than that for DF No.1 and No.3.The degradable films fulfilled successfully all the functions of the plastic film,thus they were recommended as viable option to the plastic film due to their good degradability.