Design Of Phosphorus-containing Flame Retardants And Research On Performance And Mechanism Of Unsaturated Polyester Composites

Unsaturated polyester resins(UPR)present excellent properties such as easy processing,high strength and chemical corrosion resistance.Thus,they are widely used in construction,transportation and other fields.However,there are many shortcomings in their application:UPR composed of hydrocarbons is easily ignited and generates a lot of heat and smoke hazards;The commonly used styrene diluents are volatile and cause environmental pollution,and also present problems such as flammability and high smoke density during combustion;The glass fiber used in the reinforcement system is prone to cause"wick effect"and poor bonding,which deteriorates the flame retardant and mechanical properties;The raw materials of composite materials are derived from petroleum-based monomers,which are susceptible to resource shortage and restrict their development.This paper is based on the design concept of high efficiency,safety and environmental protection,combined with the composition and structural characteristics of UPR materials,and adopts the technical means of additive flame retardant,reactive flame retardant and interface regulation to prepare flame retardant UPR composites,and systematically study its thermal stability,thermal degradation,flame retardant performance and flame retardant mechanism.The specific research work includes the following aspects:1.The effects of different phosphorus valence states,flame retardant element combination and content,and main/side chain structure of the additive flame retardant system on the thermal performance,flame retardant performance and flame retardant mechanism of UPR are studied.Preparation of polymeric flame retardant with various structures(PCH3-S?PB-S?PO-S?PCH3-A?PB-A and POA)by polycondensation between phosphorous dichloride compounds(phenyl d i ch 1 oroph osph ate,phenylphosphonic dichloride,methylphosphonic dichloride)and glycol compounds(bisphenol S and bisphenol A).First,the thermal stability of the polymerized flame retardant and the flame retardant unsaturated polyester composite was evaluated.During the heating process,there is an interaction between flame retardants and unsaturated polyester matrix through the transesterification reaction and the ?-scission mode of the styrene segment.In UL-94,15 wt%of PCH3-S would make the composites to reach V0 level.With 20 wt%of PB-S,the PHRR and THR values can be reduced by 71.66%and 77.67%.The thermal decomposition process of flame retardant and unsaturated polyester can be analyzed from gas phase and condensed phase.It has been found that flame retardants containing sulfone groups and+3 valent of phosphorus structures can release SO2 and phosphorus-containing compounds in gas phase,diluting the combustible pyrolysis products and catalyzing H.and HO·radical capture reactions.The sulfone groups and+5 valent of phosphorus structures containing flame retardants exhibit high carbonization ability,promoting the formation of carbon layers in condensed phase through pyrophosphoric acid,phosphoric acid and sulfonic acid.2.Study the preparation process of bio-based flame retardant additives(PBEG,POEG,PCH3PG,PBPG and POPG),and analyze the combined use of different phosphorus valence structures in polymerized flame retardants on the thermal stability,flame retardancy and resistance of UPR composites The influence of the combustion mechanism reveals the structural law of high-efficiency flame retardants suitable for UPR.Compared with the flame retardants with single valence phosphorus structure,the combined use of different phosphorus valence structures with the same amount of flame retardant is beneficial to the improvement of the thermal stability.When 15 wt%PBEG was added,UPR/PBEG 15%can reach V0 level in UL-94,and the phosphorus content of the UPR composite was only 2.52%.When the PBEG content was 20 wt%,the LOI value of UPR/PBEG 20%was further increased to 30%.When 15 wt%PBEG was added,the PHRR and THR values of UPR/PBEG 15%was decreased by 70.92%and 65.52%,respectively.However,compared with PBEG,the combined use of different phosphorus valence structures did not improve the flame retardant efficiency of UPR composites.Through gas phase and condensed phase analysis,it was found that the PBEG and PCH3PG flame retardants that can make UPR composites reach a higher flame retardant level are mainly based on the gas phase flame retardant mechanism,supplemented by the formation of a catalytic carbon layer and its barrier effect.In short,bio-based polymeric flame retardants significantly improve the flame retardant performance,but different phosphorus valence structures have a weaker effect on the flame retardant efficiency of UPR composites.3.Study the application of both flame-retardant and anchor group-modified glass fiber in high-efficiency flame-retardant UPR system,synthesize PKH550 phosphorus-containing flame-retardant interface modifier,surface-modified glass fiber,and combine with polymeric flame-retardant additive PCH3-S to prepare Flame retardant glass fiber reinforced UPR composite material with excellent comprehensive performance.In the study of the thermal behavior of UPR composites,it was found that the use of PKH550 did not significantly affect the T5%,T10%and Tmax of composites.At the same time,the use of PKH550 and PCH3-S was conducive to the increase of carbon residue in composites.When the amount of PCH3-S was low,MGF/UPR2 can reach V0 level,and its LOI value was as high as 37%.Compared with PGF/UPR3 which showed no level in UL-94 test and 33%LOI value,the use of PKH550 modified glass fiber makes.MGF/UPR3 reach V0 level,and the LOI value was as high as 38%.This indicates PKH550 can effectively solve the "candle wick effect" problem of glass fiber from the perspective of interfacial flame retardancy.Compared with GF/UPR,the PHRR and THR values of MGF/UPR2 were reduced by 43.97%and 43.76%respectively,which indicated that PKH550 and PCH3-S can work together to exert a better flame retardant effect.In addition,PKH550 improved the interfacial bonding between glass fiber and UPR matrix,and enhance the interface compatibility.4.Research the application of bio-based ramie fiber modified with multi-level nano-structured layers in flame-retardant UPR materials,adjust the surface double-layer metal hydroxide(LDH)structure and graft the phosphorus-containing silane coupling agent PSi,combined with bio-based flame-retardant Additive PBEG to prepare bio-based fiber-reinforced composites with excellent comprehensive performance.The tensile strength of UPR/Textile@LDH@PSi was improved,due to the reinforcing effect of ramie fabrics,the interfacial adhesion provided by the vertically grown LDH nanosheets and the good interfacial compatibility betwen PSi coating and matrix.LDH modified ramie fiber also improves the high-temperature char-forming properties of the composite material.At the same time,during the combustion process of the UPR composites,the pyrophosphoric acid formed by the decomposition of PSi and the catalysis of silicon-containing compounds and metal oxides produced from LDH help to form a carbon layer and inhibit the release of heat.The addition of bio-based flame retardant additive PBEG can make the composite material UPR3 reach UL-94 V0 level,and the LOI value is as high as 32%.The PHRR value of UPR composite material is reduced by 54.63%.This shows that the interface LDH and PSi flame retardant layer and the PBEG flame retardant in the matrix work together to enhance the flame retardant performance of composites.5.Study the application of reactive flame-retardant monomers prepared by molecular design to replace polystyrene in UPR composites.Three different non-volatile flame retardant diluent crosslinkers(PBHA,POHA and PSHA)were synthesized with different phosphorus-containing structures,which can completely replace styrene and bring excellent flame retardant performance for UPR.The structure of flame retardant diluent crosslinkers was characterized by FTIR and NMR(1H,31P).The potential of synthesized reactive diluents as substitutes in UPR and its glass fabric reinforced composites was assessed through volatility,processability,curing kinetics and gel contents.Meanwhile,by comparing the effects of different phosphorous structures,PBHA diluent can bring best flame retardant efficiency.UP/PBHA reached V0 in UL-94 and 28%of LOI.The PHRR and THR of UP/PBHA were decreased by 64.06%and 61.54%compared with neat UP/St.For glass fabric/UPR composites,GF/UP/PBHA also reached V0 rating,and LOI was as high as 38%.Meanwhile,through the study of thermal stability,thermal degradation and combustion process,it has found PBHA mainly worked in gas phase to capture H·and HO·,supplemented by promoting formation of dense carbon layer in condensed phase to isolate oxygen and thermal radiation.