Lactic acid water removal during

From a chemistry point of view, lactic acid can form PLA by means of the reaction of the hydroxyl and carboxylic acid groups of lactic acid. By removing the water formed during this condensation reaction, the reaction proceeds toward the product side, PLA ... 

The most abundant milk protein is casein, of which there are several different kinds, usually designated a-, (1-, and K-casein. The different caseins relate to small differences in their amino acid sequences. Casein micelles in milk have diameters less than 300 nm. Disruption of the casein micelles occurs during the preparation of cheese. Lactic acid increases the acidity of the milk until the micelles crosslink and a curd develops. The liquid portion, known as whey, containing water, lactose and some protein, is removed. Addition of the enzyme rennet (chymosin) speeds up the process by hydrolysing a specific peptide bond in K-casein. This opens up the casein and encourages further cross-linking. 

The first route of producing PLA is generated using a polycondensation reaction of the hydroxyl and carboxylic acid group starting from lactic acid (shown in Fig. 23.2). Water produced during the polymerization has to be removed during... 

The DPC process dehydrates lactic acid into ohgomers, which are then further polymerized to PLA with simultaneous dehydration. However, removal of water generated from the condensation of lactic add is very difficult during the final stage of polymerization because the diffusion of moisture in the highly viscous polymeric... 

Figure 2.2 Lactic acid and pH homeostasis by the bicarbonate buffer system. The bicarbonate buffer system removes protons [H ] generated during anaerobic glycolysis. The protons are disposed of as water while the CO2 evolved is expired via the lungs.

The fourth step in the manufacturing process is the polymerization of lactic acid to polylactide, or PLA. PLA can be polymerized via direct polycondensation reaction through azeotropic dehydration. High molecular weight polymers are difficult to synthesize due to the equilibrium between the free acids, water, and the polymer. Dean-Stark trap can be used to remove excess water during the reaction. m-Xylene can be added to lactic acid that added together in a flask at 138 C for 30 hours. After water is removed, the Dean-Stark trap can be replaced with a molecular sieve to recycle the azeotropic mixture. The resultant mixture can be polymerized to PLA at 138°C (Kim and Woo 2002). 

Similar to the synthesis of poly(lactic acid), the polycondensation of glycolic add is the simplest process available to prepare PGA but it is not the most efficient one because it yidds low-molecular-wdght products. The procediue is as follows glycolic add is heated at atmospheric pressiue and a temperature of about 175-185 C during a time necessary for removing water. Subsequently, the reaction pressure is reduced... 

Crude lecithin is mixed with 2-14% hydrogen peroxide and 1% lactic acid at 50-60 °C. The lactic acid reduces the pH, which facilitates the reaction. Residual water is removed by drying. During the reaction the coloured components are bleached, which yields a light coloured lecithin. Hydroxylated lecithin is superior for emulsification of oil-in-water emulsions. It easily disperses in cold and water as a whitish emulsion. This is already a good indication that the HLB value increased significantly. 

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