Preparation And Properties Of Substrate For Growth And Culture Of Biodegradable Polymer Composites

Soilless cultivation can effectively prevent soil continuous cropping obstacles and soil-borne diseases,improve crop yield and quality,save water and fertilizer,save labor,not limited by natural conditions,its application and development has attracted more and more attention in the world.At present,soilless cultivation at home and abroad has too large initial investment,difficult preparation of nutrient solution,complicated management,complicated technology,non-biodegradable,high production cost.The growth and culture substrate of biodegradable polymer composite developed in this paper is a soilless culture substrate of double cross-linking and double network hydrogel,which integrates fertilizer and substrate with controllable holes.The production cost is low,and it can solve the problems of single nutrient of growth culture substrate and difficult degradation of growth culture substrate material,which may cause secondary pollution to the environment.In this study,polyvinyl alcohol(PVA)and sodium alginate(SA)solutions were used as raw materials,and chemical pore-making agent calcium carbonate(Ca CO₃)and pore-making agent citric acid(C₆H₈O₇)were used to prepare Ca²⁺-PVA/SA-Mu controllable pore double cross-linking double network hydrogel culture matrix by chemical pore-making assisted low-temperature pore-making method.The effects of conventional hydrogel SA/PVA and different proportion of growth medium on fresh weight,dry weight and emergence rate of seedlings were studied in rapeseed culture experiment.The change of structure,mechanical properties and weight loss rate of biodegradable polymer composites with different ratios of SA and Ca²⁺in different days was studied,and the performance of plant growth substrates with different ratios was systematically studied.The specific experimental research content of this dissertation is described as follows:(1)Using PVA and SA solutions as raw materials,the pore-making agent calcium carbonate(Ca CO₃)and the pore-making agent citric acid(C₆H₈O₇)as chemical pore-making agents,and the pore-making assisted low-temperature pore-making method were used to prepare Ca²⁺-PVA/SA controllable pore double cross-linking double network hydrogel medium.By adding hydroxymethylurea(MU)and calcium dihydrogen phosphate(Ca(H₂PO₄)₂)to provide nutrients for plant growth,a soillless culture matrix with Ca²⁺-PVA/SA-MU fertilizer with controllable holes and a double cross-linking double network hydrogel was prepared.(2)Rape culture contrast experiment was set with conventional hydrogel SA/PVA,SA:Ca²⁺=10:1,20:1,30:1,40:1,50:1 Ca²⁺-SA/PVA-MU double cross-linked double network hydrogel culture substrate.The effects of conventional hydrogel SA/PVA and growth substrate with different ratio of SA and Ca²⁺on fresh weight,dry weight and seedling emergence rate of seedlings were studied.The germination rate of Ca²⁺-SA/PVA-MU double cross-linked double network hydrogel was better than that of conventional SA/PVA hydrogel culture substrate.When SA:Ca²⁺-MU=40:1,the germination rate of rapeseed seeds reached100%on the 5th day,and the fresh and dry weight was heavier on the 7th day,the root length was longer and the growth was the best.(3)The change of N,P release rate,structure,mechanical properties and weight loss rate of the growth matrix with different ratio of SA and Ca²⁺was studied.The cumulative release rates of N and P of biodegradable polymer composites in water showed that the cumulative release rates of N and P were the highest when SA:Ca²⁺=10:1,and the lowest when SA:Ca²⁺=40:1.SEM images of SA:Ca²⁺=40:1 biodegradable polymer composites before planting,after seedling and 20 d showed that the porosity of SA:Ca²⁺=40:1biodegradable polymer composites had little change and remained relatively good with the increase of days.At the same time,the amount of pores to meet the needs of plant respiration.Compressive strength tests showed that the compressive strength increased as the number of days increased.The weight loss rate of biodegradable polymer composites with SA:Ca²⁺=10:1-50:1 in soil increased first and then decreased.