PVA films

Polarized IR spectra in PVA film, and the calculated (SCRF) spectra of 7-methyl- and 9-methyladenine, 17 and 18 (R = Me) respectively, have demonstrated that they exist as the amino forms shown [97JPC(A)4361],... 

Figure 3 Formation model of porous PVA film from PVAc latex.

In this Section, we describe two complex deformations due to electric field-associated swellings. One is the bending of a hybrid gel consisting of a PVA-PAA gel rod and a PVA film in dc fields. The hybrid gel has been used to fabricate a smart gel finger. The other is the vibration of PVA-PAA gel film in ac fields. This new deformation suggests a gel having a fast response on the order of 100 ms. 

The excited-state lifetime calculated for TINS in PVA film is found to be 1.3 + 0.1 ns compared with 44 4 ps found in the case of water (H). This supports the earlier proposal that complexation, which is proposed to occur in protic, hydrogen-bonding solvents, does not occur in this polymer. In the PVP film an intense fluorescence and a long excited-state lifetime, similar to that found for TINS in PVA, is observed and is consistent with the ESIPT process being prevented in this aprotic medium. 

PVA film/ Sodium alginate/ Proteolytic enzyme Protease C (Pr)+ polyhexamethyleneguanidine hydrochloride [PHMG], as antimicrobial (AM) -biological active material -decreases the rate of inactivation of Pr by 2 times -decrease the amount of desorbed AM by 10 times, giving the film self-disinfecting properties. 236... 

PVA film/ Tetraborate (TB)/ Proteolytic enzyme Protease C (Pr)+, a cationic polymeric antimicrobial (AM=Metacid) 235... 

PVA films have high water-vapor permeability (water-vapor-transmission coefficient PH2o is 270 g 0.1 mm/10 h m2 cm-Hg) [294] that increases rapidly with relative humidity and with decrease in the hydrolysis degree. 

The objective of this work is to determine the surface concentration of the hydroxyl groups of cellulose and PVA films utilizing their chemical modification. We chose these polymers mainly because the hydroxyl group is their sole functional group. Recently we have reported that a cellulose film is more excellent in wettability towards water than PVA, though cellulose is insoluble in water, in contrast to PVA(4). Since only the chemical composition of the surface must be responsible for water... 

Figure 4. Contact angle 6 of cellophane and PVA films as a function of phenyl-urethanation time (---) cellophane (----) PVA (O, ,) receding ( .If) ad-...

It should be also pointed out that both of the cellulose films have the same urethane surface concentration of 2.0 x 10 mol cm 2 at saturation, irrespective of the presence of catalyst, whereas the PVA film has half the surface concentration of cellulose. 

Figure 11. Surface concentration (Cs) of the hydroxyl groups o-naphthyluretha-nated with or without tin octoate for cellulose and PVA films (O) Visking without catalyst (0) Visking with tin octoate (Q) cellophane without catalyst (A)...

Surface Modification of Cellulose and PVA Films. Cellulose, as well as PVA,is known to be a typical non-ionic, hydrophilic polymer possessing hydroxyl groups. As this group has a high reactivity,chemical modification of these polymers is relatively easy and, in fact, has been the subject of extensive research. However, so far as we know, no work has been reported concerned with reactions occurring only at the surface of films or fibers from these polymers. 

Surface Concentration, Cs, of the Hydroxyl Groups Urethanated for Cellulose and PVA Films and Surface Area, As, per Hydroxyl Group... 

Oxygen Availability in Degrading Films. A major difference between natural materials and starch-plastic or cellulose-plastic blends is that the hydrophilic and relatively permeable matrix of materials like wood and hydrated polysaccharide films allows diffusion of O2 and release of nutrients from sites at a distance from the invasion site. As colonization proceeds, pore enlargement occurs when the pore walls are degraded (8) or as the polymer matrix of amylose or PVA films is hydrolyzed (10.12). In contrast, the LDPE matrix supplies no nutrients, hinders diffusion of water and O2, and the pore diameter cannot be increased. The consequence of impermeability is that the sole means of obtaining O2 and nutrients is by diffusion through water-filled pores. 

Samples were excited with 30-ps 600-nm excitation flashes (< 100 11J 1.5-2 mm diameter) at 5 Hz. The maximum standard deviation in AA was typically 0.005. Rps. sphaeroides reaction centers (36) and polyvinyl alcohol (PVA) films (17) were prepared as described previously. 

Figure 1. Near-infrared absorption changes for Rps, sphaeroides reaction centers imbedded in a PVA film at 30 ps (A) and 1,6 ns (B) with respect to the center of a 30-ps 600-nm excitation flash, at 295 K (dashed) and 5 K (solid). Reproduced with permission from Ref. 22. Copyright 1985, Elsevier Science Publishers.

Figure 3. (A) Absorption changes in the BPh region at 30 ps and 1.6 ns at 5 K. (B) Difference between the 30-ps and 1.6-ns spectra. (C) Ground-state spectrum of the same PVA film in this region at 5 K. Reproduced with permission from Ref. 35.

Figure 4 shows the temperature dependence of the decay kinetics measured in PVA films in the 665-nm band (triangles). Some measurements at lower temperatures in the 545-nm band are also shown (circles). The electron transfer rate constant increases by a factor of 2 as the temperature is lowered from 295 K to 100 K, at which point the rate becomes independent of temperature within experimental error. The solid curve through the experimental data in Figure 4 is a theoretical fit that will be discussed below. 

The time constants measured near 665 and 795 nm at 295 K in PVA film are in good agreement with those measured at 285 K in flowed buffer (Table 1). Even though the kinetics are different at different wavelengths, the temperature dependence in each region appears to be similar the time constant decreases by about a factor of two between 295-285 and 76 K, and is the same at 76 and 5 K. 

PVA films buried in soil were tested after 120 days and showed only very limited signs of biodegradation, and even field tests with PVA sheets buried for 2 years in different natural soil sites showed only limited (10%) weight loss. No traces of colonising microorganisms were detected on the incubated material. Degradable polymers like poly(hydroxy butyrate), PCL or starch are usually extensively... 

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