Study On The Performance Of Phenolic Foam Modified By Larch Tannin And Cork Powder

Phenolic resin foamed material has excellent thermal insulation performance and fire resistance,but its toxic and non-renewable raw material,high friability,easy pulverization,poor toughness,low mechanical performance,and other shortcomings limit its applications.Phenol was replaced with larch tannin in varying amounts to prepare larch tannin-based foamable phenolic resins and foamed materials,and the larch tannin-based phenolic resin foamed materials were modified by adding cork powder during foaming process in this research.The main conclusions were summarized as followed:(1)The composition,chemical structures and thermal stability of larch tannin were characterized by Fourier transform infrared spectroscopy,carbon nuclear magnetic resonance spectroscopy,and so on.The molecular structure of larch tannin was composed of dominant procyanidin units,a minor amount of prodelphinidin units,and polyphenol dimer units.A small proportion of substitution with glucose and gallic acid was detected in larch tannin.The different polymer chain length distributions of larch tannin can be up to 11 repeating units.The units of larch tannin were linked together by a C4-C8 bond,and the A-rings were mainly the type of phloroglucinol.The thermograms of larch tannin revealed two obvious mass losses.(2)The depolymerization processes of larch tannin under the acidic condition were studied.The chemical structures,molecular weight and thermal stability of depolymerization products were characterized.The optimized acid depolymerization conditions allowed the efficient depolymerization of larch tannin into monomers and/or oligomers at 60 0C,for 2 h,using 2-mercaptoethanol as the nucleophile,with 0.1 mol/L catalyst concentration.The thermal stability of depolymerized larch tannin was enhanced.Many compounds of molecular weight less than 600 Da,mainly dimers and monomers,were obtained under these reaction conditions.Compared with acid-catalyzed depolymerization,larch tannin obtained a better depolymerization effect under the condition of sodium sulfite,and its products are more suitable for the preparation of tannin-based phenolic resin and foamed material.(3)A green and environment-friendly sulfite alkaline depolymerization method was employed to depolymerize larch tannin to prepare larch tannin-based foamable phenolic resins and foamed materials.The spectra of the foamed materials were also similar to those of the resins,indicating a similarity in chemical structures.The fire resistance of larch tannin-based phenolic resin foamed materials was improved,but it exhibited poorer cell morphology,toughness,and mechanical performance,compared with pure phenolic resin foamed materials.(4)Cork powder reinforced foamed materials were prepared by adding cork powder during foaming process of larch tannin-based phenolic resins.Cork powder served as a nucleation agent during foaming process,and had a significant effect on the enhancement of foamed materials.The chemical structures of larch tannin-based phenolic resin foamed materials were similar to those of cork powder-reinforced larch tannin-based phenolic resin foamed materials.The cell morphology,mechanical performance,and toughness of the latter were improved.The foamed materials which exhibited the best comprehensive features was the larch tannin-based phenolic resin foamed materials reinforced with 1%cork powder,which presented a mean cell size of 221.41 ?m,and a cell density of 9.64×104 cells/cm3.The compression strength and modulus increased by 14.84%and 16.18%,respectively;the pulverization ratio and thermal conductivity of CLTPFs decreased by 18.4%and 32.29%,respectively,relative to those of unmodified larch tannin-based phenolic resin foamed materials.