Study On Depolymerization Of Larix Gmelinii Proanthocyanidins With Palladium-based Catalyst

Proanthocyanidins are one of the most important secondary metabolites in plants.They have abundant sources of renewable raw materials and are promising plant product raw materials that can be developed into a variety of functional chemicals.However,due to the shortcomings of high degree of polymerization and large molecular weight of proanthocyanidins,their application fields are greatly restricted.In this paper,Pd/C-SO₃H and Pd/SO₄^2-/ZrO₂ were used as catalysts for the catalytic hydrogenolysis of proanthocyanidins.The average degree of polymerization and the yield of depolymerization were used as indicators to evaluate the effect of catalytic depolymerization.The depolymerized product and polymer materials were combined to prepare a new type of thermally-induced conductive shape memory material.The research work carried out is as follows:The activated carbon was sulfonated to C-SO3H,and Pd was supported in the C-SO3H framework by a reduction method.The multi-functional composite catalyst was used to catalyze the depolymerization and extraction of larch bark proanthocyanidins.After X-ray diffraction?XRD?,pHysical adsorption analyzer?BET?,scanning electron microscope?SEM?,thermogravimetric analyzer?TG?characterization and stability test,it was found that the catalyst Pd/C-SO₃H was successfully prepared,and has good thermal stability,cycling and acid and alkali resistance.In the experimental range,the best depolymerization conditions are:reaction temperature 220?,reaction time 2h,hydrogen pressure 5MPa,catalyst dosage is 0.25%?g/mL?,At this time,the average degree of polymerization of the depolymerized product was 3.14,and the depolymerization yield was 55.58%.Ultraviolet spectroscopy?UV?,infrared spectroscopy?FTIR?,and nuclear magnetic hydrogen spectroscopy?1H NMR?showed that the depolymerized product was still a condensed flavanol-like polypHenol structure,and the basic structural units were the same before and after depolymerization,and did not change.The main way to break the bond is to break the C4-A8 bond.X-ray pHotoelectron spectroscopy?XPS?and inductively coupled plasma mass spectrometry?ICP-MS?analysis showed that the content of Pd in the depolymerized product was very small,meeting the national food safety standards.Anti-oxidation performance experiments show that the anti-oxidation of the depolymerized product is not only stronger than before depolymerization,but also stronger than the common antioxidant 2,6-di-tert-butyl-4-methylpHenol?BHT?.The scavenging rate of the depolymerized product to DPPH·radicals can reach 77.1%,and the scavenging rate to ABTS·radicals can reach 98.4%.The zirconium oxychloride octahydrate was hydrolyzed into Zr?OH?4,and then sul fated into a SO₄^2-/ZrO₂ support.Pd was supported in the SO₄^2-/ZrO₂ framework by reduction method.The multifunctional composite catalyst was used to catalyze depolymerization of larch bark.After X-ray diffractometer?XRD?,specific surface area analyzer?BET?,scanning electron microscope?SEM?,X-ray pHotoelectron spectroscopy?XPS?,thermogravimetric analyzer?TG?characterization and stability test,it was found that the catalyst Pd/SO₄^2-/ZrO₂ was successfully prepared,and has good thermal stability,cycling and acid and alkali resistance than Pd/C-SO₃H.In the experimental range,the optimal depolymerization process conditions are:reaction temperature 220?,reaction time 3h,hydrogen pressure 5MPa,and catalyst dosage is 0.25%?g/mL?.At this time,the average polymerization degree of the depolymerization product is 1.91.The polymerization yield was 74.46%.Ultraviolet spectroscopy?UV?analysis and molecular weight distribution?GPC?analysis showed that the molecular weight of the depolymerized product had a significant decrease,and it was still a condensed flavanol polypHenol structure,and the basic structural unit was not damaged.Experiments with reducing ability,DPPH·,ABTS·free radical scavenging ability showed that the anti-oxidation performance of the depolymerized products and proanthocyanidins before depolymerization were stronger than the antioxidant 2,6-di-tert-butyl-4-methylpHenol?BHT?,The scavenging rate of DPPH· free radicals by the depolymerization products can reach 89.5%,and the scavenging rate of ABTS·free radicals can reach 99.2%.Finally,the depolymerized product was solvent blended with nitrile rubber?NBR?to develop a conductive shape memory material?L-NBR?with thermal response effect.The material can be repeatedly deformed and recovered under conditions above the glass transition temperature?50??.With the increase of the content of depolymerization products,the glass transition temperature of L-NBR gradually increased;FTIR analysis showed that chemical cross-linking occurred between the depolymerized product and the nitrile rubber;When the content of the depolymerized product is 20%,the shape memory effect of L-NBR is the best,the mechanical tensile properties,the aging resistance and the UV resistance are the best.Thermogravimetric?TG?analysis shows that L-NBR greatly improves the understanding of the thermal stability of the polymer.In addition,a layer of silver nanoparticles was coated on the surface of the L-NBR to give it conductivity.The L-NBR was restored after multiple twists,and its conductivity was almost the same as before the twist,indicating that the new thermotropic conductive shape memory material was successfully prepared.The material can be stretched and twisted.It is not only an electrical conductor,it can maintain the pHysical properties of rubber elastomers,and it has excellent antioxidant and UV resistance of proanthocyanidins,which can be applied to the electronic skin and intelligent components of modern simulation robots.