Steady-State and Dynamic Fluorescence Emission from Abies Wood

Steady-state and single-photon timing fluorescence experiments performed on thin sections of Abies wood which have been reduced and non-reduced by sodium borohydride show that wood luminescence is fluorescence and is mainly due to lignin

The use of alkyl cinnamates as UV screens for preventing the photo-yellowing of lignin-rich pulps

A number of alkyl cinnamates and related compounds have been synthesized. Upon irradiation in solution, some of the materials undergo cis-trans isomerization and a cycloaddition reaction. Application of these compounds to lignin-free paper does not suppress these reactions. The cinnamates were evaluated as UV screens for preventing the photo-yellowing of the lignin-rich paper. None of the compounds proved to be highly effective, and this result is important for a deeper understanding of the role of UV screens for preventing the light brightness reversion of high-yield pulps

Attempts to Photostabilize Paper Made from High-Yield Pulp by Application of UV Screens Containing Groups to Aid their Compatibility with Cellulose and Lignin

2,4-dihydroxybenzophenone (DHB) is known to be a reasonably efficient UV screen for preventing the colour reversion of papers made from high-yield pulps. Attempts have been made to improve the performance of this material by increasing its compatibility with cellulose and by the introduction of cationic groups which will help it to locate in lignin-rich areas. The latter has proved successful and the results show that, on a molar basis for the 2,4-dihydroxybenzophenone nucleus, the efficiency is increased by the introduction of ammonium and thiouronium groups. An interesting finding was that a 2,4-dialkyloxyderivative of benzophenone showed similar protective power to that observed for DHB

Environmentally friendly films based on chitosan and tetrahydrocurcuminoid derivatives exhibiting antibacterial and antioxidative properties

Environmentally friendly films exhibiting both antibacterial and antioxidative properties were elaborated from chitosan and tetrahydrocurcuminoids (THCs). Two tetrahydrocurcuminoids, THC1 (5-hydroxy-1,7-bis(4- hydroxy-3-methoxyphenyl)hept-4-en-3-one) and THC2 (5-hydroxy-1,7-bis(4-hydroxy-3,5-dimethoxyphenyl)hept-4-en-3-one), were incorporated into a chitosan film. THC1 could be prepared from natural curcumin extracted from turmeric roots (Curcuma longa L.). The resulting tetrahydrocurcuminoid-chitosan films exhibited a high free-radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) in methanol, which was due to a progressive release of the THCs into the solvent. The release kinetics was governed both by molecular interactions between chitosan and THCs and probably by electrostatic forces between the ammonium units in chitosan and the aromatic rings in THCs. These interactions were clearly evidenced by the presence of new absorption bands in the visible regions of the electronic absorption spectra of the THCs. The molecular nature of these interactions was shown using glucosamine, the main monomer of chitosan. When associated with THCs, chitosan retained its bioactivity against Listeria innocua; THCs alone were not bioactive enough against listerial strains

Comparative-Study of Stone-Ground Wood Pulp and Native Wood .2.Comparison of the Fluoresence of Stone-Ground Wood Pulp and Native Wood

The fluorescence spectra of paper made from high yield pulp (stone-ground wood pulp (SGWP)) and of thin sections of a softwood (Abies) were recorded and shown to be very similar. The fluorescence from a wood sample, previously reduced with sodium borohydride, shows a biexponential decay, with the magnitude and contribution of the components being dependent on wavelength. From the bleaching kinetics of the chromophores producing the fluorescence, it is concluded that the emission observed for paper made from high yield pulp and for wood originates mainly from lignin and not as previously suggested from cellulose. The steady state and dynamic fluorescence of some lignin model molecules adsorbed on cellulose indicates that the fluorescence of wood, which has been reduced by sodium borohydride, might -originate to some extent from coniferyl alcohol and biphenyl-type structures

The action of phloroglucinol in the presence of hydrochloric acid on photoaged, totally-chlorine-free, bleached chemical pulps

UV-Vis diffuse reflectance spectrometry has been used to monitor the reaction of phloroglucinol (in the presence of hydrochloric acid) with totally-chlorine-free (TCF) bleached softwood bisulfite chemical pulps. Pulps (1-4) bleached via various sequences, which include ozone and hydrogen peroxide processes, were studied. The unirradiated pulps show a very small absorption band with a maximum at about 460 nm when the phloroglucinol test was performed. Pulp 3, which was bleached only with peroxide and contains the higher amount of lignin (Kappa number,4), displays, after ageing with UV light and after the phloroglucinol test, a broad absorption band with a maximum at 560 nm, similar in behaviour to photodiscoloured lignin-rich pulps. Pulp 2, bleached by one ozone stage followed by a peroxide stage (Kappa number, 1.7) displays the same trend (broad band centred at 560 nm) although the lignin content was lower. This indicates that the phloroglucinol test is very sensitive to oxidized lignin. Pulps 1 and 4, which were fully bleached (Kappa number, 0.5 or less), still present a narrow absorption band around 555 nm after irradiation with UV light. The origin of this band remains uncertain. ortho-Quinone models adsorbed on cellulose paper appear to be insensitive to the phloroglucinol test, in contrast to 2-methoxy-para-quinone and coniferaldehyde. Such chromophores are probably formed by UV irradiation of the TCF pulps