The main objective of the project is to use available European wood resources for manufacutre of high yield pulps usable in papers with improved brightness stability compared to pulps available today. A secondary objective is to broaden basic knowledge on the yellowing of paper and apply the results in couteracting colour reversion.
The object of the project is to make high yield pulps with improved colour stability and to broaden the understanding of the yellowing process and its inhibition, thus promoting production of papers with improved stability from European Wood.
Various groundwood and refiner type pulps were made from softwood and several hardwood species. The influence of the pulping reagents and conditions during the manufacture on the optical and mechanical properties were established using both sulphonation and peroxide pulping. Subsequently the pulps were also bleacehed in various ways. The results point to the need to compromise between optimum bleaching conditions with regard to brightness and stability. The experiences led to pilot scale paper making with poplar chemithermomechanical pulp. This paper showeed excellent optical properties, was successfully used for sizing and coating trials with yellowing inhibitors.
In the studies on brightness stabilization, ultraviolet screens and antioxidents were synthesized and used, together with commercial ones and then applied to pulps, pulp fractions and papers.
The output of the project was extraordinarily large and the results of the research have been spread to the pulp and paper industry in the form of reports, publications, seminars and courses. Patents have been granted and they have been offered to the industry.
. Background. To intensify the use of
European forest resources, particularl
y of hardwood, the papermaking potenti
al of relevant species should be evalu
ated. Accordingly, various modern meth
ods of pulp preparation should be appl
ied, such as CMP, CTMP, TMP, PGW and s
team explosion. The potential of such
pulps in printing and writing paper wo
uld also increase if colour reversion
(yellowing) could be effectively dimin
These studies require some process res
earch, such as study of the defibratio
n mechanism using various types of equ
ipment, as well as work with various t
ypes of raw material, untreated and ch
Although colour reversion has been stu
died extensively bleaching has been fo
und to be economically feasible but de
trimental to the colour stability, and
use of additives to be potentially ef
fective but uneconomical - no practica
l application has yet been developed.
The basic research is concerned with i
nitial precursors of chromophores in t
he lignin and their reactions during t
he bleaching and on irradiation by lig
ht, thus enlarging the existing knowle
dge of pathways leading to yellowing.
Pulp modification, and pulp and paper
protection to increase their brightnes
s stability should be studied simultan
Plans. The project is planned to focus
on two parts: firstly, on preparation
of high-yield pulps and secondly, on
prevention of colour reversion.
The first part will include preparatio
n of CMP/CTMP from European trees and
coppice-wood both as single species an
d in mixtures, followed by evaluation
of papermaking properties of the pulps
. In addition to these refiner-based p
rocesses, stone groundwoods of differe
nt kinds from softwood and steam explo
sion pulps from hardwoods will be exam
The colour reversion task includes stu
dies on pulps prepared in connection w
ith the high-yield pulping investigati
ons and on other relevant pulps regard
ing their behaviour towards light.
Actions to prevent discolouration - by
inhibition, retardation or 'masking'
imply use of additives (light absorber
s, antioxidants and scavengers) within
the paper or on its surface as e.g. c
oatings, use of multilayer technique a
nd so on. The mechanisms of photoyello
wing of lignin, sulphonated lignin and
lignin model systems will be studied
separately by photochemical and spectr
Funding SchemeCSC - Cost-sharing contracts
EC1V 0HB London