Regeneration And Utilization Of Waste Phenolic Formaldehyde Resin And Its Performance Study

Recycled thermosetting phenolic formaldehyde（RPF） resins were pulverized as micron-sized powders and successfullly reused as an effective component by reactive-injecting with neat phenolic formaldehyde（PF） resins to prepare regenerated phenolic formaldehyde（i.e.PF_xRPF_y^w） materials having acceptable mechanical stengths and other required properties.In addition,the optimum curing temperature and curing time were found by reactive injection.More than 35% of the ground RPF powders are between 200 to 400 mesh(RPF²⁰⁰);while nearly 60%of the ground RPF powders are between 400 and 800 mesh(RPF⁴⁰⁰)and nearly 1.2% of the ground RPF powders are more than 800 mesh(RPF⁸⁰⁰) after jet milling processes.Trioxymethylene（TOX） was firstly reaction-injected with PF resins and RPF pulverized powders to improve the mechanical strengths of the regenerated PF/RPF/TOX（i.e.PF_xRPF_y^wTOX_z） materials.Tensile strength（σ_f）,impact strength（I_s）,specific weight（ρ） and shrinkage percentages of PF_xRPF_y^w and PF_xRPF_y^wTOX_z specimens reduced significantly as RPF concentrations or particle sizes increased;while their water absorption contents increased significantly with increasing RPF concentrations or average particle sizes.It is worth emphasizing that σ_f,I_s,ρ and shrinkage percentage values of each reaction-injected PF_xRPF_y^wTOX_z series having a fixed RPF concentration and particle size improved to a maximal value;while W_a values decreased to a minimal value,as TOX concentrations reached an corresponding optimal value.This is the first investigation exhibitting that σ_f and I_s values of regenerated PF/RPF and PF/RPF/TOX specimens using more 20wt% RPF waste were ≥95% of those of the reaction-injected PF specimen.Possible reasons accounting for the above interesting improved mechanical and other properties for PF_xRPF_y^w and PF_xRPF_y^wTOX_z materials were proposed based on the results from scanning electron microscope（SEM）,Fourier transform infrared analysis（FTIR）and Solid-state nuclear magnetic resonance ¹³C spectra analysis（SSNMR） of the PF,RPF^wand reaction-injected PF PF_wRPF_y^x and PF_xRPF_y^wTOX_z specimens.FTIR and SSNMR analysis showed that the crosslinking reaction was mainly between -CH₂OH functional groups of PF during the reactive injection processes,and the PF after curing was mainly linked by -CH₂-.Some cross-linked RPF will be activated after -CH₂-was broken by mechanical pulverizing.The RPF^w powder and PF could be activated after added poper TOX concentrations,and some possible crosslinking reaction occurred between functional groups of PF,RPF^w and TOX.We can infer the possible reaction mechanism between PF,RPF^w and TOX according to the analysis of FTIR and SSNMR.