Preparation Process And Flame Retardant Properties Of Miscanthus Floridulus/Bio-Based Epoxy Resin Composites

Climate and environmental concerns require reducing the use of traditional high-carbon emitting petroleum-based plastics.Biodegradable composite materials derived from biomass offer significant environmental advantages and cost-effectiveness,making them a research hotspot in the composite materials field.This thesis uses the rich source of Miscanthus floridulus as raw material and improves the flame retardancy of bio-based epoxy resin by nitrogen-phosphorus co-ordination complex metal ion modification to prepare bio-based composite materials,thereby improving the flammability of epoxy resin.Through chemical modification of Miscanthus floridulus and preparation of composite materials,this study investigates the curing reaction process and its impact on mechanical,thermal,and combustion properties,resulting in the preparation of composite materials with excellent flame retardancy,as well as good mechanical and thermal properties.The main research content and results are as follows:（1）Structural characterization and performance research of Miscanthus floridulus（MF）,providing theoretical basis for the utilization of MF biomass materials.Three components of Miscanthus floridulus,stem,leaf,and tassel,were selected for component and structural research,and compared the differences in composition,structure,and crystallinity.In terms of major components,all three parts are composed of cellulose,hemicellulose,and lignin,with stem having the highest proportion of cellulose and tassel having the highest proportion of lignin.The differences in elemental composition among the three components are not significant,with carbon being the main element,followed by oxygen,and the sum of carbon and oxygen accounting for more than 95%.In addition,there are trace elements such as nitrogen,phosphorus,and sulfur.In terms of functional group composition,stem,leaf,and tassel all contain characteristic functional groups such as hydroxyl,carbonyl,and benzene ring,and stem and tassel also have their unique functional groups,aromatic ether in stem and N-H,-CH₃,-CH₂-in tassel.In terms of crystal structure,the main crystal structures of these three components are caused by the typical I-type structure of natural cellulose,with the highest crystallinity in stem,followed by leaf and the lowest in tassel.In terms of thermal stability,stem has the best low-temperature thermal stability,while tassel has the best high-temperature thermal stability,mainly related to the composition ratio of cellulose and lignin in the material and crystallinity.The low-temperature stability of stem is better due to its higher cellulose crystallinity,while the high-temperature stability of tassel is mainly due to its higher lignin content.（2）The first part of the study revealed that Miscanthus floridulus stems have a high proportion of cellulose,numerous pores,high crystallinity,and good thermal stability,making them more suitable for biomass flame retardant modification.The surface modification of MF fibers was achieved through vacuum-pressure impregnation of polyethyleneimine（PEI）and phytic acid（PA）by electrostatic self-assembly,followed by the introduction of barium ions to prepare a Miscanthus-based expanded flame retardant（PEI-PA-Ba-MF）.This surface modification method helps to enhance the fiber’s thermal stability.Analysis of the curing reaction kinetics of the Miscanthus floridulus/bio-based epoxy resin system revealed that the addition of both unmodified and modified fibers lowers the activation energy（E_a）of the epoxy resin,with E_a showing a gradient decrease with increasing amount.This indicates that surface modification of MF promotes the curing reaction of the bio-based epoxy resin.The optimal curing process for this system was determined to be 90℃ for 6 h followed by 135℃ for 1 h.（3）Pure bio-based composite materials（EP/PEI-PA-Ba-MF）were prepared using the above curing process.The thermal properties of the composite materials with different flame retardant additive ratios were analyzed,and the results showed that the composite material containing 15%surface-modified MF fibers（EP/15PEI-PA-Ba-MF）exhibited excellent flame retardancy.The flame retardancy level reached the highest V-0 rating according to the UL-94 standard,with an oxygen index of 26.4%.The peak heat release rate（pHRR）,total heat release（THR）,smoke release rate（SPR）,and total smoke production（TSP）were reduced by 71.90%,61.85%,55.0%,and 60.94%,respectively,compared to EP.The residual carbon rate at 800℃ was 15%,and the generation rate of harmful gases was reduced,while smoke generation was suppressed.The flame-retardant mechanism is that in combustion,MF acts as a natural carbon source,PEI generates flame-retardant gases,which dilutes the concentration of combustible gases,and also has a foaming effect,forming an expanded,porous carbon layer.PA captures the free radicals generated during combustion,inhibiting chain reactions,and generates a phosphorus-containing carbon layer that insulates heat and gas exchange.Ba²⁺catalyzes the carbon layer,further improving its quality.In terms of mechanical properties,the tensile,bending,and impact strengths of EP/15PEI-PA-Ba-MF were 43.78MPa,64.91 MPa,and 15.71 KJ/m²,respectively.Although slightly lower than pure EP,they increased by3.35%,11.26%,and 10.24%,respectively,compared to unmodified composite materials with the same ratio.