Plasticizer evaporation

A series of modulus-time curves was also made for temperatures covering the entire viscoelastic spectrum. At higher temperatures, the instrument was first allowed to reach the desired temperature and was held there for half an hour. Samples were then quickly inserted. After 10 minutes moduli were measured as a function of time up to 1000 seconds. Total measuring time for each isotherm thus was kept to less than 30 minutes to minimize chemical decomposition and plasticizer evaporation. 

Metal ring with plastic evaporated Front cover ... 

Rates of plasticizer evaporation are 10 to 100 times slower than typical diffusion rates. If plasticizer has good compatibility and good wetting characteristics for particular solid surface its surface spreading will hamper diffusion because diffusion is gradient controlled. Theories to explain surface deposition and its effect on plasticizer diffusion are yet to be developed. 

Thermogravimetrical analysis provides information on loss of mass which may be a result of degradation with volatilization of plasticizer component, plasticizer evaporation, or degradation and volatilization of any other component of the tested mixture (most likely polymer and stabilizer because test formulations are usually kept simple). Beeause of these different reasons for mass loss the results are difficult to interpret. In some studies reported here, evaporation loss of plasticizer was distinguished from loss of degradation products by ranning two separate tests one for the pure plasticizer and the other for the entire composition. This may help to better understand reasons for mass loss but it... 

Spectral analysis of volatile products shows that pure plasticizer evaporates before thermal degradation of PVC is recorded.Kinetic models of PVC thermal decomposition for interpretation of thermogravimetric data were proposed and verified by experimental data. ... 

Ejy activation energy of plasticizer evaporation E activation energy of PVC degradation. 

Plasticizer evaporation during thermogravimetric analysis is given by the equation ... 

Many thermoplastics become britde at room temperature, which severely limits their utility. This is true of PVC. Pure PVC is highly susceptible to cracking at room temperature and is therefore useless for most appUcadons. To avoid this problem, the polymer can be prepared in the presence of small molecules called plasticizers. These molecules become trapped between the polymer chains where they function as lubricants. Common plasticizers are dialkyl phthalates, such as di-2-ethylhexyl phthalate used in vinyl upholstery, raincoats, shower curtains, inflatable boats, and garden hoses. Some plasticizers evaporate slowly with time, and the polymer ultimately returns to a britde state in which it can be easily cracked. Intravenous (IV) drip bags used in hospitals are typically made from PVC with plasticizers. 

Shower curtains ate made from PVC, which is a thermoplastic polymer. To prevent the polymer from being brittle, the polymer is prepared in the presence of plasticizers which become trapped between the polymer chains where they function as lubricants. Over time, the plasticizers evaporate, and the polymer becomes brittle. 

Other. Because a foam consists of many small, trapped gas bubbles, it can be very effective as a thermal insulator. Usually soHd foams are used for insulation purposes, but there are some instances where Hquid foams also find uses for insulation (see Eoamed plastics Insulation, thermal). Eor example, it is possible to apply and remove the insulation simply by forming or coUapsing the foam, providing additional control of the insulation process. Another novel use that is being explored is the potential of absorbing much of the pressure produced by an explosion. The energy in the shock wave is first partially absorbed by breaking the bubbles into very small droplets, and then further absorbed as the droplets are evaporated (53). 

Emissions During Processing. During the production of flexible PVC products plasticizers are exposed for up to several minutes to temperatures of - ISO C. The exact conditions depend on the processing technique employed, but it is evident that the loss of plasticizer by evaporation and degradation can be significant. 

Emissions During Exterior End Use. When flexible PVC is used in exterior appHcations plasticizer loss may occur due to a number of processes which include evaporation, microbial attack, hydrolysis, degradation, exudation, and extraction. It is not possible, due to this wide variety of contribution processes, to assess theoretically the rate of plasticizer loss by exposure outdoors. It is necessary, therefore, to carry out actual measurements over extended periods in real life situations. Litde suitable data have been pubHshed with the exception of some studies on roofing sheet (47). The data from roofing sheet has been used to estimate the plasticizer losses from all outdoor appHcations. This estimate may weU be too high because of the extrapolation involved. Much of this extracted plasticizer does not end up in the environment because considerable degradation takes place during the extraction process. 

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