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1、Natural Latex天然胶乳-胶乳英文,Natural LatexControl and Industrial Procedures,Emily Liu Material Science,Natural Latex天然胶乳-胶乳英文,Natural Latex,A. Introduction,B.Control Procedures,Natural Latex天然胶乳-胶乳英文,Introduction,Centrifuged latex is processed into final articles by dipping, extruding, and coating. Differ
2、ent articles have different physical and chemical requirements, which means that the latex used in their manufacture must be modified by the addition of a great variety of substances that give each formulation its unique characteristics. These characteristics are well-specified and must be carefully
3、 controlled.,Natural Latex天然胶乳-胶乳英文,Example of a Control Sheet for LATZ Latex,Natural Latex天然胶乳-胶乳英文,An example of a control sheet for the type of natural rubber latex that is commonly used in making surgical gloves is given in the Table 1.,The purpose of this PPT： We explain briefly how some of the
4、se characteristics are controlled.,Natural Latex天然胶乳-胶乳英文,Control Procedures,3,4,5,6,Dry Rubber Content (DRC),Surface Tension,pH Measurement,Mechanical Stability,KOH Number,Total Solid Content (TSC),Viscosity,2,7,1,Natural Latex天然胶乳-胶乳英文,Control Procedures,1.Determination of the Total Solid Content
5、(TSC) of Latex,Add your title in here,The TSC of latex is obtained by drying a sample of the liquid latex to be assayed and weighing the residue. The value obtained is the sum of the dry rubber content plus the solid nonrubber contents, which includes the protein. Latex that is used in the productio
6、n of gloves, catheters, and so on has a TSC of 6062%.,Natural Latex天然胶乳-胶乳英文,The DRC of latex is obtained by coagulating the rubber in the sample of latex to be assayed with acetic acid, then drying, washing and weighing the resulting mass of rubber.,The difference between the TRC and the DRC is a m
7、easure of the of natural latex.,The difference between the TRC and the DRC is a measure of the total nonrubber contents of the latex. These latter constituents are principally latex proteins, lipids, and mineral salts. In the case of HA and LATZ latexes, those are commonly used in the production of
8、gloves, the nonrubber constituents make up between 1% and 2% of natural latex.,2.Determination of the Dry Rubber Content (DRC) of Latex,Natural Latex天然胶乳-胶乳英文,3. Measurement of Surface Tension,Determination of the surface tension of latex is a very useful measure, as surface tension is a function of
9、: 1. The amount of soap added to stabilize the latex; 2. The natural soaps formed after concentration from fatty acids in the lipid phase of the latex; 3. The mineral salts (mg/Na) that are present in the latex.,A low surface tension value indicates good stability, although for use in dipping system
10、s this could lead to a tendency to form webs of rubber.,Natural Latex天然胶乳-胶乳英文,The pH of fresh latex is close to neutrality. It will change more or less rapidly owing to the presence of microorganisms and enzymes, leading to progressive acidification of the latex and eventually to spontaneous coagul
11、ation. Because ammonia is added to preserve the latex, that is, to prevent coagulation, pH determination is important, as the stability of the liquid latex depends to a great degree on its pH.,4. pH Measurement,Natural Latex天然胶乳-胶乳英文,In addition, ammonia has an indirect influence on stability, incre
12、asing colloidal stability through the formation of fatty acid surfactants. When the pH of a latex is less than 9.5, which may occur, especially in the case of LA latex, then the pH must be watched very closely, frequently having to be increased chemically when it is received and siphoned at its fina
13、l destination.,Natural Latex天然胶乳-胶乳英文,The KOH number is a measure of the concentration of acid radicals that would have been present as free acids were it not for the presence of ammonia that has converted them to ammonium salts. Since some of these acids are produced by microorganisms, a poorly pre
14、served latexone with too many microorganismswill tend to have a high KOH number.,A high KOH number is not, however, necessarily indicative of a poorly preserved latex ,because this test does not distinguish between the ammonium salts of the acids whose anions destabilize latex and those that enhance
15、 stability.,5. KOH Number,Natural Latex天然胶乳-胶乳英文,The KOH number is, nevertheless, an index of the quality of the latex. A high KOH number is usually taken as evidence of degradation of the latex owing to hydrolysis of proteins occurring after too long a period in storage. For example, a very fresh l
16、atex arriving in Europe after 6-10 wk in transport from the Far East might have a KOH number of 0.04-0.05, whereas an aged latex would have a KOH number of 0.70-0.8 on arrival. The KOH number of centrifuged or creamed latexes must not exceed 1.0.,Natural Latex天然胶乳-胶乳英文,Mechanical stability is define
17、d as the resistance of the latex to flocculation during stirring or agitation. It is measured by the mechanical stability time (MST) test in which latex is stirred rapidly (14,000 rpm) under standardized conditions and the time required for visual flocculation to occur is noted.,6. Measurement of Me
18、chanical Stability,Expressed in seconds, this test allows the behavior of the latex to be evaluated during the course of the different operations it undergoes during its transformation into a finished product. The mechanical stability of natural latex should be 650 s.,Natural Latex天然胶乳-胶乳英文,Mechanic
19、al stability tends to decrease during long periods of transportation and storage owing to the slow hydrolysis of the stabilizers by the ammonia. It is therefore necessary to be very prudent when a natural latex is received and found to have low mechanical stability, for example, 600 s. Such a latex
20、is susceptible to the formation of grains and will be filterable with difficulty. Manufacturers generally avoid this problem by adding stabilizers such as an anionic fatty acid alcohol, for example, lauryl sulfate.,Natural Latex天然胶乳-胶乳英文,Among the physico-chemical properties of latex, viscosity is o
21、ne of the most important with respect to the production and processing of latex products. The viscosity of a fluid is the ratio of the shear stress to the shear rate during its flow.,7. Viscosity,Most latexes exhibit decreasing viscosity with increasing shear rate and for this reason any reference t
22、o latex viscosity should include a description of the method of measurement, the rate of shear and the test temperature.,Natural Latex天然胶乳-胶乳英文,The viscosity of a particular latex is a function of its origin, including the clone from which it was derived, and of the composition of the latex serum, i
23、ts total solids concentration, and the means of preservation.,Natural Latex天然胶乳-胶乳英文,Company Logo,Other Test,Natural Latex天然胶乳-胶乳英文,Example of a Control Sheet for LATZ Latex,Natural Latex天然胶乳-胶乳英文,For additional information, refer to: Latex Technology and Processing Natural Rubber Technical Information,Natural Latex天然胶乳-胶乳英文,Thank you,此课件下载可自行编辑修改，供参考！ 感谢你的支持，我们会努力做得更好！,