Film forming processing solvent casting

Rhim et al. (2006) compared two different methods for obtaining PLLA films, i.e. solvent casting and thermocompression. In the first case, dried PLLA pellets were dissolved in chloroform at room temperature. The solution was spread on a casting surface (made of Teflon) and allowed to dry for 24 h at room temperature. In the thermocompression process, PLLA was placed in a press formed by two plates of stainless steel lined with aluminum foil, heated to 190 °C. Then, a pressure of about 69 MPa was applied for 3 min. Using the solvent-casting method, PLLA films retained up to 10% of the solvent, which acted as a plasticizer and affected film properties. Thermocompressed film showed a greater thermal stability and better mechanical properties moreover, they did not contain residual solvent. 

Since poly(L-tyrosine) cannot be processed into shaped devices, compressed pellets rather than solvent cast films were used as control implants. Poly(L-tyrosine) formed strikingly yellow, moderately inflamed patches that remained at the implantation site throughout the 1-year study. Contrary to soluble proteins or peptides that ar rapidly degraded by enzymes, implants of conventional poly(L-tyro-sine) were evidently nondegradable over a 1-year period. At wee 56 all poly(L-tyrosine) implants were infiltrated by a moderate n ber of inflammatory cells. 

It is interesting to note that, in most cases studied, the range of hydroxyl content in PS(OH) which allows the miscibility-to-complex transition to take place in solvent-cast films is almost the same as that allowing separate coils to transform to complex aggregates in solutions [143]. This agreement suggests that complexes formed in dilute solutions remain undestroyed during the process of solvent evaporation. 

THV Fluoroplastic can be processed by virtually any method used generally for thermoplastics, including extrusion, coextrusion, tandem extrusion, blown film extrusion, blow molding, injection molding, vacuum forming, and as skived film and solvent casting (only THV-220). 

Cellulose acetate is the most important cellulose ester and various processing techniques for forming shaped bodies exist for this polymer. The mixed esters discussed above, CAP and CAB, are used predominantly for injection moulding applications in suitably plasticized form and are marketed as pellets. This is done for CA as well, but additionally, alternative processing routes are available where solution methods play an important role. This is in particular the case for fibre spinning and (thinner) film manufacture where cellulose diacetate (CDA) is dissolved in acetone and dry spun or solvent cast. Moreover, the traditional solventusing block process is employed for obtaining sophisticated, multicoloured thick sheets for applications like spectacle frames. 

In the PANI.TSA/PLA blended electrospun nanofibers no phase segregation of PANI in a PLA matrix was observed, while phase segregation was observed in cast films with the same composition. Due to rapid solvent evaporation in the electrospinning process, no crystalline structures in fiber mats were formed compared to cast films. Highly homogeneous electroactive fibers can be useful in the construction of electronic devices and sensors. Similar behavior was observed in the PVDF-TrFE/PANI-PSSA electrospun nanofibers. 

Separation processes such as ultrafiltration and micro filtration use porous membranes which allow the passage of molecules smaller than the membrane pore size. Ultrafiltration membranes have pore sizes from 0.001 to 0.1 )im while micro filtration membranes have pore sizes in the range of 0.02 to 10 im. The production of these membranes is almost exclusively based on non-solvent inversion method which has two essential steps the polymer is dissolved in a solvent, cast to form a film then the film is exposed to a non-solvent. Two factors determine the quality of the membrane pore size and selectivity. Selectivity is determined by how narrow the distribution of pore size is. In order to obtain membranes with good selectivity, one must control the non-solvent inversion process so that it inverts slowly. If it occurs too fast, it causes the formation of pores of different sizes which will be non-uniformly distributed. This can be prevented either by an introduction of a large number of nuclei, which are uniformly distributed in the polymer membrane or by the use of a solvent combination which regulates the rate of solvent replacement. 

The development of foams for medical purposes was described by Radusch [193], To eliminate thermal degradation, as well as to avoid the problems associated with the low melt viscosity, a process was developed based on solvent casting and subsequent particle leaching. Well-defined porous structures can be formed in such a way [197-200], for example, PHB was dissolved in chloroform, the ensuing solution was mixed with water-soluble particles like NaCl, films were then prepared by solvent casting and evaporation and, subsequently, the salt particles were washed out with water. Various foamed structures were thus prepared, depending on the particle size and amount, as well as other parameters, such as the PHB type and its concentration in the chloroform solution. 

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