| Natural rubber latex is the largest source of latex raw material for latex products,such as gloves,condoms and nipples,which has a great film forming property.The analysis of the factors influencing the film forming properties of natural latex have important theoretical and practical significance for optimizing the film forming process of natural rubber latex and improving the quality of natural rubber latex products.The effects of proteins and phospholipids on the properties of natural rubber latex and the properties of film were studied in this paper.In this paper,the centrifugal concentrated natural rubber latex(C-CNRL),deproteinized natural rubber(DPNR),lipid-free natural rubber(PNR)and lipid-free DPNR(P-DPNR)were prepared by high speed refrigerated centrifugation,treatment with enzyme decomposition(alkaline protease,lipid enzyme)and high speed centrifugation.After centrifugation and enzyme treatment,the nitrogen content of P-DPNR decreased from 0.2718%to 0.0014%,and the lipid content decreased from 4.8990%to 2.1049%,combined with the results of infrared spectrum,the analysis showed that the alkaline protease and lipase can effectively remove the proteins and phospholipids on the surface of the natural rubber particles.The particle size distribution is concentrated and the average particle size becomes larger,the average molecular weight of DPNR and PNR decreased by 1.33 × 105?1.34 × 105,molecular weight distribution became wider.After centrifugation and enzyme treatment,the drying rate of film increased.The moisture contents of CNRL,C-CNRL,DPNR,PNR,and P-DPNR at 60 min were 0.52,0.38,0.24,0.17and 0.11.It can be seen that P-DPNR has the fastest water loss.DPNR and PNR film drying rate is greater than CNRL.The thermal stability of the adhesive film was detected by thermogravimetric analyzer,the results showed that:the initial degradation temperature of DPNR and PNR reduced to 347.70 ??349.46 ?,thermal stability deterioration.Detection results of vulcanization characteristics of adhesive film showed that the optimum cure time t90 of DPNR and PNR increased from 15.10min to 22.02 min and 25.37 min,t90 was obviously longer,and the vulcanization speed was slower.Atomic force microscopy(AFM)was used to observe the surface morphology of the adhesive film,and the surface morphology of the film tended to be flat,the roughness of DPNR and PNR decreased from 29.9 nm to 16.7 nm and 15.6 nm after one day(24 h).The influence of proteins and phospholipids on latex film formation process was analyzed,and the mechanism chart of film formation process was put forward.It is mainly divided into four steps:water evaporation phase,particle deformation phase,coalescence phase,and inter-diffusion phase.The W3/031 water vapor transmission rate tester and the 0X2/230 oxygen transmission rate test system was used to detect the tightness of the film.The airtightness test results of the film showed that:after centrifugation and enzyme treatment,the water vapor transmission rate of film reduced,the oxygen transmission rate increased.UV Vis NIR spectrophotometer was used to detect the transmittance of film,the results showed that the transmittance of DPNR and PNR increased from 71.12%to 85.31%and 85.62%respectively.The physical and mechanical properties of the adhesive film were detected by tensile testing machine,the results showed that the tensile properties of DPNR and PNR decreased from 25.14 Mpa to 15.81 Mpa and 16.57 Mpa,the elongation of DPNR and PNR increased from 810.6%to 930.8%and 895%.Besides,the detection results of nuclear magnetic resonance cross-linking density showed that the crosslinking density of DPNR and PNR decreased from 3.46*E-4molˇmL-1 to 2.76*E-4molˇmL-1 and 2.81*E-4molˇmL-1.The SEM results indicated a small amount of holes and particles appear in the tensile section of the adhesive film.Comprehensive analysis demonstrated that that proteins and phospholipids influence the formation of the natural rubber crosslinking between molecular chain network,thus affecting the properties of the film. |
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