High-yield pulp

Kringstad, K. (1969). Degradation of wood and high-yield pulps by light—a survey of the present state of knowledge. Tappi, 52(6), 1070. 

Young, R.A. (1977). Modification of high-yield pulps by the xanthate method. Journal of Agricultural and Food Chemistry, 25(4), 738-742. 

The quinonemethide content of chemically modified lignins may be much higher. If quinonemethide precursors (—e.g. structures of type III) are present in high yield pulps in residues of condensed lignin attached to the fibers, attempts to bleach the pulps with oxidizing agents may lead... 

Schmidt, J.A., Heitner, C., "Light-Induced Yellowing of Mechanical and Ultra-High Yield Pulps. Part I. Effect of Methylation, NaBH Reduction and Ascorbic Acid on Chromophore Formation , J. Wood Chem. Technol., 1991,11(4) 397. 

Kringstad, K.P., Lin, S.Y., "Mechanism in the Yellowing of High-Yield Pulps by Light. Structure and Reactivity of Free Radical Intermediates in the Photodegradation of lignin", Tappi, 1970, 53(12), 2296. 

Forssk hl, I., Olkkonen, C., TYLLI, H., "Singlet Oxygen Induced Bleaching of High Yield Pulp Sheets", J. Photochem. Photobiol., 1988, 43, 337. 

Mechanical and ultra-high yield pulps are used primarily for low-value, short-life grades of paper such as newsprint and advertising, catalog, and directory papers. Their use in more valuable paper products is severely restricted by the rapid yellowing which occurs upon exposure to daylight, a phenomenon which is attributed to the photooxidation of lignin. 

Formation of Leucochromophores during High-Yield Pulping and H202 Bleaching... 

Little work has been carried out so far to characterize the lignin structures present in various types of high yield pulps. Model compound experiments have... 

It is relevant to note that the effect has been observed in all the high-yield pulps that we have studied. The study included commercial unbleached and peroxide-bleached spruce groundwood, unbleached and peroxide-bleached spruce and aspen chemimechanical pulp (Table I). 

Table I. Brightness Change (% R, 457 nm) during Storage (24 h) after Irradiation (1 h) of High-Yield Pulps...

The observed phenomenon, which we interpret as a photochromic effect, can in principle result in an instant photoyellowing of high-yield pulps upon exposure to ultraviolet irradiation. 

Our conclusion is that the photochromic behaviour of high-yield pulps is due mainly to the formation of colour-generating radicals. These radicals can for example be of the phenoxy or semiquinone type, present in the high molecular part of the lignin. However, the contribution of cis-trans isomerization reactions can not be excluded. 

Lebo, S. E. The Occurrence and Light-Induced Formation of ortho- Quinoid Structures in High Yield Pulp Lignins. Doctor s Dissertation, Appleton, Wisconsin, 1988 p 31. 

Ek, M. Some Aspects on the Mechnisms during Photoyellowing of High-Yield Pulps. Doctor s Dissertation, Stockholm, Sweden, 1992 p 107. 

Photocycling of Chromophoric Structures during Irradiation of High-Yield Pulps... 

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