| 1. |
- Axegard, Peter, et al.
(författare)
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Bleaching of softwood kraft pulps with H2O2, O3, and ClO2
- 1996
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Ingår i: TAPPI Journal. - 0734-1415. ; 79:1, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- Ozone or chlorine dioxide bleaching prior to hydrogen peroxide bleaching greatly improves the performance of the hydrogen peroxide stage. The efficiency is further improved by a chelating treatment immediately after the ozone or chlorine dioxide stage. With an optimal metal ion profile, laboratory bleached (OAZQP) softwood kraft pulps can reach brightness levels above 90% ISO, with 5-10% lower pulp strength properties and bleaching costs comparable to ECF bleaching. It also is possible to obtain full brightness with only hydrogen peroxide provided the metal ion profile is optimal, e.g., by using multiple QP treatments. The chemical consumptions, expressed as oxidation equivalents per decreased kappa number are the same as for sequences including ozone or chlorine dioxide. Ozone and chlorine dioxide are comparable as far as delignification and brightness efficiency go.
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| 2. |
- Buchert, Johanna, et al.
(författare)
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Significance of xylan and glucomannan in the brightness reversion of kraft pulps
- 1997
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Ingår i: TAPPI Journal. - 0734-1415. ; 80:6, s. 165-171
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Tidskriftsartikel (refereegranskat)abstract
- The brightness reversion of kraft pulps is caused by the presence of residual lignin, chlorinated extractives, or oxidized carbohydrates. The effect of hemicellulose content, i.e., xylan (I) and glucomannan (II), on the thermal stability of modern bleached kraft pulps was investigated. Different O-delignified hard- and softwood kraft pulps were bleached with different bleaching sequences contg. ClO2, H2O2, or O3. Hemicellulose-degrading enzymes, i.e., xylanase or mannanase, were used for selective removal of the resp. hemicellulose from the pulps, and the role of partially removed I and II on the brightness stability of these pulps was studied. Because of the structure of kraft I, enzymic removal of I also resulted in a decreased carboxyl group content in the pulps, whereas II removal did not affect the carboxyl group content. By decreasing the carboxyl groups in the pulps in conjunction with I removal, the thermal aging of the pulps was significantly decreased. The role of II was less significant. Thus, the uronic acids present in the pulp participate in the brightness reversion of kraft pulps.
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| 3. |
- Buchert, Johanna, et al.
(författare)
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The role of xylan and glucomannan in yellowing of kraft pulps.
- 1995
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Ingår i: Proceedings 8<sup>th</sup> Int. Symp. Wood Pulp. Chem.. ; , s. 43-48
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Konferensbidrag (refereegranskat)abstract
- The effects of xylan and glucomannan on the thermal stability of unbleached, partially bleached, and fully bleached pine and birch kraft pulps were studied. The choice of bleaching chems. strongly affected the brightness reversion. Compared with hydrogen peroxide or chlorine dioxide, bleaching with ozone reduced the amt. of carboxyl groups and subsequently the pc-nos. of oxygen-delignified pulps. Xylan removal reduced also the amt. of carboxyl groups in the pulps and this was reflected in improved brightness stability whereas glucomannan removal had no effect. Thus, the uronic acids bound to pulp xylan were found to participate in the brightness reversion of kraft pulps.
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| 4. |
- Ek, Ulla, et al.
(författare)
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Relation between blindness due to retinopathy of prematurity and autistic spectrum disorders: a population-based study.
- 1998
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Ingår i: Developmental Medicine and Child Neurology. - 0012-1622. ; 40:5, s. 297-301
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Tidskriftsartikel (refereegranskat)abstract
- Children with blindness due to retinopathy of prematurity (ROP)--who are at greatly increased risk of cerebral damage--have been noted to have a high rate of autistic symptoms, but systematic controlled studies have been lacking. A controlled population-based study was performed; one group was blind due to ROP (N=27) and the other was congenitally blind due to hereditary retinal disease (N=14). Fifteen of the 27 children with ROP had autistic disorder. All these children were mentally retarded and about one-third of them had cerebral palsy. In the comparison group, two of the 14 children had autistic disorder. It is concluded that there is a strong association between ROP and autistic disorder. The association is most probably mediated by brain damage and is largely independent of the blindness per se.
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| 5. |
- Jacobson, Lena, et al.
(författare)
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Children with blindness due to retinopathy of prematurity: a population-based study. Perinatal data, neurological and ophthalmological outcome.
- 1998
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Ingår i: Developmental Medicine and Child Neurology. - : Wiley. - 0012-1622 .- 1469-8749. ; 40:3, s. 155-159
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Tidskriftsartikel (refereegranskat)abstract
- A population-based group of 27 children with total blindness due to retinopathy of prematurity (ROP), born in Sweden from 1980 to 1990, was examined. They constituted all but two of the total of 29 children with total blindness due to ROP known to the national register of visually impaired children when reviewed from 1980 to 1 January 1995. All children had a gestational age of less than 31 weeks and most had had a complicated perinatal period. The retinal disease was discovered late, most often after it had already progressed to bilateral retinal detachment. Repeated vitreoretinal surgery had been performed in most children, but postoperative visual function did not improve. Three-quarters of the group had major neurological impairment (mental retardation, cerebral palsy, or epilepsy) at age 4 to 14 years. There was an impression that extensive ophthalmological efforts delayed neurodevelopmental assessments and examinations as well as adequate habilitation.
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