Study On Photocatalytic Degradation Of Polyisoprene Based On Graphite Phase Carbon Nitride And Its Ultrafiltration Separation Of Skim Latex

Skim latex is the separation product of natural rubber latex via the method of concentrated procedure.The common method of separation is that adding formic acid and sulfuric acid to the skim latex for the solidification and recover of the gelatin.But following problem is the produce of large amount of acid waste water leading to environmental pollution.Membrane separation technology can effectively avoid the generation of acid wastewater in the application of separation of skim latex.The polyisoprene in component of natural rubber in the skim latex makes the latex with high viscosity and serious membrane pollution,which limits the application of membrane separation technology in the separation of rubber clearings.In this paper,a carbon nitride composited porous catalyst was designed,and GQDs/g-C₃N₄and GQDs/g-C₃N₄/[Ru]-Ⅱcatalysts were prepared under controlled method to photocatalyze the degradation of cis-polyisoprene and natural rubber latex.1H-NMR,GPC,FT-IR and UV-Vis methods were used to analyze the degradation mechanism of natural rubber,and ultrafiltration membrane was used to separate the rubber.Photocatalysis promoted the degradation of skim latex and effectively reduced the viscosity of skim latex.This method alleviated membrane contamination and increased membrane permeation flux.The specific research contents are as follows:（1）GQDs/g-C₃N₄composited photocatalyst with porous nanoparticle structure was prepared by microwave assisted thermal polymerization.The catalytic degradation process of cis-polyisoprene（PI）with different catalyst dosage was studied.FT-IR spectroscopy and GPC were used to analyze the degradation products and discuss the degradation mechanism.The molecular structure of PI was changed after 0.5 h of light exposure.After 10 days of photocatalysis,the molecular weight of PI decreased from 15.49×10⁴to 8.78×10⁴.The molecular weight of PI mixed with GQDs/g-C₃N₄was reduced to 5.79×10⁴under the same lighting conditions.In the process of photooxidation,the breakdown of the crosslinking network in PI leads to the decrease of the molecular weight of the long chain fracture.The carbon-carbon double bond is broken for further reactions to form aldehydes and ketones,leading to the formation of new groups.The addition of photocatalyst increased the degradation efficiency by 34%,indicating that GQDs/g-C₃N₄nanoparticles promoted the generation of free radicals and accelerated the degradation of PI.（2）Exploring the photocatalytic conditions of step（1）,the GQDs/g-C₃N₄composited catalyst was applied to the degradation of natural latex.The degradation process of natural latex under different light time was discussed.¹H NMR,GPC,FT-IR and UV-Vis were used to characterize the degradation products of natural latex.The results showed that the molecular weight of natural latex decreased from 13.41×10⁴to 8.53×10⁴after ultraviolet degradation for 10 days,and decreased to 6.51×10⁴after adding GQDs/g-C₃N₄composite catalyst.In the process of natural latex photodegradation,the oxidation reaction starts fromα-H,α-H is attacked by oxygen to produce peroxides,and the generated peroxides further react to form aldehydes and ketones,and generate unsaturated conjugate structures.Under the action of photocatalyst,the formation of·O^2-is accelerated.After the chain of polyisoprene is broken,it interacts with·O^2-free radicals and further oxidized and degraded,resulting in the reduction of molecular weight.（3）GQDs/g-C₃N₄/[Ru]-Ⅱcomposite catalyst was prepared by melt composite method and used to degrade natural latex.The degradation process of natural latex by GQDs/g-C₃N₄/[Ru]-Ⅱunder photocatalytic conditions and the mechanical properties of natural rubber corresponding to natural latex with different molecular weight were investigated,and the degradation mechanism was analyzed.The results show that GQDs/g-C₃N₄nanoparticles adhere to the fused[Ru]-Ⅱspherical surface.Compared with the catalytic effect of（2）,the addition of[Ru]-Ⅱaccelerated the degradation of natural latex.After 10 days of photodegradation,the molecular weight of natural latex decreased from13.41×10⁴to 4.98×10⁴.Due to the olefin compound decomposition reaction induced by metal catalyst,the carbon-carbon double bond broke during the cycle.In this way,alcohols,aldehydes,ketones and other functional groups are generated,resulting in the degradation of macromolecular rubber hydrocarbons in natural latex into short chain rubber hydrocarbons.The second generation catalyst combined with GQDs/g-C₃N₄has higher activity,and the degradation effect is better than that of simple photocatalyst.（4）The separation of skim latex by ultrafiltration membrane with photocatalysis was studied.The ultrafiltration membrane separation system was established according to the principle of osmotic pressure.PVDF ultrafiltration membrane was used to filter and separate the photocatalyzed skim latex.The separation performance of ultrafiltration membrane was evaluated by membrane pollution and viscosity after separation.The results showed that the molecular weight of the skim latex decreased after photodegradation,and the viscosity of the skim latex increased from 3.3Mpa/s to 5.4Mpa/s when the transmembrane pressure difference was 0.02Mpa and the feed flow rate was 40L/h.The membrane specific flux remained at0.054 after the filtration cycle for 30min.The membrane specific flux of the ultrafiltration membrane was 0.037.The results showed that the recovery effect of the concentration of the skim latex was obviously better under the condition of photocatalysis.