Ultraviolet-induced crosslinking of poly(vinyl alcohol) in the presence of sensitizers

Abstract

SynopsisUltraviolet-induced crossliking of the film of polyvinyl alcohol with different degrees of polymerization was investigated in air a t 25°C. in the presence of sodium benzoate as a sensitizer.In the absence of the sensitizer, no crossliing occurred. The gel content increased with irradiation time, and tended to a limiting value, depending on the initial sensitizer concentration. The final gel content increased as a function of the initial amount of sodium benzoate. A plot of solubility ( S + AS'/^) against the reciprocal of the concentration of sensitizer converted gives a straight line in each caae. The number of crosslinks is directly related to the number of sensitizer molecules destroyed. The crosslinking occurred predominantly, and main-chain scission was negligible. This result is in marked contrast to the effect of ionizing radiation, since the ionizing radiation causes only degradation under the identical conditions. This ultraviolet method waa applied successfully to the crosslinking of water-soluble cellulose derivatives, such as methyl cellulose and sodium carboxymethyl cellulose.Crossliing is always accompanied by photolysie of the sensitizer.

Ultraviolet‐induced crosslinking of poly(vinyl alcohol) evaluated by principal component analysis of FTIR spectra

“…The FTIR spectra of original PVA and PVA irradiated for 4 h are shown in Fig 1; they show that the absorption intensities at 1596 cm −1 (assigned to the CC stretching vibrations of the benzoate ring) and 1552 cm −1 (corresponding to the asymmetric carboxylate anion stretching) of sodium benzoate decreased after exposure to irradiation, indicating that the sensitizer was photo‐decomposed. These results are in agreement with previous studies8 using UV spectrophotometry to measure effects of irradiation on PVA in the presence of sodium benzoate. Takakura et al 8 detected spectral changes suggesting that, on irradiation, the sensitizer is initially converted to an intermediate (with an absorption maximum at a somewhat higher wavelength), which is further decomposed to a radical sufficiently reactive to abstract a hydrogen atom from the polymer.…”

“…These results are in agreement with previous studies8 using UV spectrophotometry to measure effects of irradiation on PVA in the presence of sodium benzoate. Takakura et al 8 detected spectral changes suggesting that, on irradiation, the sensitizer is initially converted to an intermediate (with an absorption maximum at a somewhat higher wavelength), which is further decomposed to a radical sufficiently reactive to abstract a hydrogen atom from the polymer. The FTIR spectra also show that the absorption intensities at 1388 cm −1 decreased after exposure to the irradiation.…”

“…After an exhaustive bibliographical study, it was verified that the mechanism of crosslinking is not completely elucidated at present. However, it is probable that a free radical arising from the photolysis of sodium benzoate would abstract a tertiary hydrogen atom from the polymer chain to yield a polymeric radical, which can crosslink by combination with another such radical 8…”

Preparation and characterization of surface crosslinked TPS/PVA blend films

“…Since PVA contains a number of hydroxyl groups, and it was demonstrated that PVA can be photocrosslinked under UV irradiation when using sodium benzoate as sensitizer (Follain et al, 2005;Takakura, Takayama, & Ukida, 1965). Therefore, it is worthy to apply the surface photocrosslinking modification method (Zhou et al, 2008) in TPS/PVA blend system to improve physical properties of the blend.…”

Changes induced by UV radiation in the presence of sodium benzoate in films formulated with polyvinyl alcohol and carboxymethyl cellulose

“…These processes can lead to the cross-linking of PVOH molecules, making the polymer more insoluble in water. The most efficient photosensitizer is sodium benzoate (SB), known to be photolysed by UV radiation [21,22]. Excitation of photoinitiator produces reactive radicals which initiate subsequent reactions in the polymer blend thus facilitating cross-linking between the two polymer chains [16].…”