Preparation Of Bionic Porous Sponge Substrates Modified By Polycaprolactone Study On Its Performance

Soilless cultivation is a cultivation method that requires integration and sustainability and is rapidly developing in arid or water-scarce regions around the world.Polyurethane sponges are widely used in the construction industry,automobiles,agriculture,and other fields due to their many advantages,such as light weight,low cost,and simple manufacturing.The non-degradation of traditional polyurethane sponges will cause pollution to the environment and an irreversible impact on ecology,and degradable modification is required.Polycaprolactone is a thermoplastic crystalline polyester obtained by ring-opening polymerization of caprolactone,is a fully biodegradable material,has good biocompatibility,and non-toxicity,is widely used in the medical field.At present,polycaprolactone polyurethane sponge has the advantages of degradability and toughness,but it has the disadvantages of poor water absorption and low compression strength.At the same time,it cannot provide nutrients for plants,so it needs further modification to meet the requirements of soilless cultivation substrate.In this study,polycaprolactone glycol(PCL-2000),polycarbonate glycol(PCDL-2000),4,4’-diphenylmethane diisocyanate(MDI)and potassium humate(KHA)were used as the main raw materials,and a series of degradable soilless sponge substrates PCL-PCDL-PUF and PCL-PCDL-PUF/KHA were prepared by the one-step method.To increase the nutritional function of the matrix,nitrogen(L-tyrosine)and phosphorus(disodium β-glycerophosphate)were prepared to modify PCL-PCL-PUF/KHA sponge matrix(N-PCL-PCDL-PUF/KHA,P-PCL-PCDL-PUF/KHA).Infrared spectroscopy,nuclear magnetic resonance hydrogen spectroscopy,thermal stability,mechanical properties,XRD,XPS testing and water absorption and water retention performance,pore size,and porosity analysis were performed on the four synthetic matrices.Enzymatic degradation was used to explore the degradation performance of materials and their effects on the physiological and biochemical indexes of lettuce planting during use.The results of the study are as follows:(1)PCDL-PUF/KHA was modified with biodegradable material polycaprolactone(PCL-2000)in a one-step method.A series of degradable PCL-PCDL-PUF/KHA sponge substrates were prepared by mixing PCL/PCDL according to mass ratios of 0:10,2:8,5:5,8:2 and 10:0.FT-IR,XRD and XPS were used to demonstrate the successful preparation of degradable porous sponge matrix.When the mass ratio of PCL/PCDL was 5:5,the optimal apparent density was 65.58 kg/m3,the optimal porosity was 96.58%,the average pore size was 0.40±0.10 mm,the compressive strength was 0.012 MPa,and the water absorption factor was 112.24 g/g.It was found that the introduction of humic acid potassium through physical blending would not affect the thermodynamic properties of PCL-PCDL-PUF/KHA sponge.Although its apparent density,porosity,pore size distribution and compressive strength were reduced,its water absorption and retention properties were improved.After exploration,it was found that the optimal formula of synthetic PCL-PCDL-PUF/KHA sponge was 50 g PCL,50 g PCDL,2.0 g silicone oil L-580,1.4g/0.4 g A33/T-12,4.0 g H2O and 1.0 R-value.(2)PCL-PCDL-PUF/KHA sponge has degradation properties but cannot have positive effects on plants.Therefore,nitrogen-containing small molecules(L-tyrosine)and phosphorus-containing small molecules(disodiumβ-glycerophosphate)that can be absorbed by plants were chemically modified into PCL-PCDL-PUF/KHA sponge.FT-IR,NMR,XRD and XPS proved that the synthetic PCL-PCDL-PUF/KHA sponge matrix modified by nitrogen and phosphorus was successfully prepared.XRD analysis showed that the amount of nitrogen and phosphorus modified did not affect the crystallization properties of the composite.Through polarizing microscope observation,uniform small pores appeared on the surface of the sponge.When the nitrogen modifier content was 3%,the optimal apparent density was 65.69 kg/m3,the porosity was 85.58%,and the pore size distribution was 0.96±0.17 mm.After thermal performance analysis,the residual carbon content was the lowest,the maximum thermal decomposition temperature was 320.73℃,the water absorption ratio was 125.24 g/g,and the water retention capacity was the best.When the amount of phosphorus modifier was 1%,the maximum apparent density was 59.68 kg/m3,the porosity was 89.14%,and the pore size distribution was 0.91±0.13 mm.The increase of phosphorus modifier dosage will not affect the thermodynamic properties of P-PCL-PCDL-PUF/KHA sponge.The optimal compressive strength was 0.014 MPa and the optimal water absorption ratio was 115.62 g/g.In the overall analysis,the apparent density,porosity,and pore size distribution of the N-PCL-PCDL-PUF/KHA sponge were better than those of the P-PCL-PCDL-PUF/KHA sponge.(3)After 6 months of enzymatic degradation performance of the four sponge matrices prepared,the degradation rate of P-PCL-PCDL-PUF/KHA was 16.67%,the degradation rate of N-PCL-PCDL-PUF/KHA sponge was 10.97%,the degradation rate of PCL-PCDL-PUF/KHA sponge was 10.0%.and the degradation rate of PCL-PCDL-PUF sponge was 8.04%.The morphology of the matrix was observed by SEM,and it was found that the matrix surface was wrinkled and the bubble was torn.Cream lettuce was grown using synthetic PCL-PCDL-PUF,PCL-PCDL-PUF/KHA,N-PCL-PCDL-PUF/KHA,P-PCL-PCDL-PUF/KHA sponge,and at 42 days of planting,The chlorophyll content of N-PCL-PCDL-PUF/KHA sponge lettuce was 0.48 g/g,and the soluble protein content of P-PCL-PCDL-PUF/KHA and N-PCL-PCDL-PUF/KHA sponge lettuce was similar to vitamin C.The experiments showed that the modified N-PCL-PCDL-PUF/KHA and P-PCL-PCDL-PUF/KHA could promote the growth of lettuce,degrade slowly during lettuce planting and release small molecules containing nitrogen and phosphorus to provide nutrients for lettuce.