Tertiary Amines in Catalytic Pulp Bleaching

The motif of the current study arises from the importance of the paper in Finland as one of the core industries. The latest released statistics reported by the Confederation of European Paper Industries (CEPI) confirms that Finland, by producing 28.5% of pulp production, possesses the second rank in terms of the production of pulp among all members of the CEPI. Pulp bleaching as one of the subcategories of the tremendous paper industries aim at producing high quality paper with three fundamental goals: the pulp maintains its color over the time; it does not revert color by exposing to the sunlight; and retains its strength. With these goals, sodium hypochlorite bleaching was initiated in the 18th century which was later replaced by chlorine in 1930s. Environmental concerns prompted this industry to opt the Elemental Chlorine Free (ECF) and the Totally Chlorine Free (TCF) bleaching processes, which alleviate the concerns about the release of organochlorine compounds. Nowadays, the ECF with chlorine dioxide is the dominant technology worldwide. Consequently, in this thesis we present a couple of catalysts which introduce a significant reduction in the retention time of the ECF bleaching processes and concurrently bring in a considerable decrease in the chemical consumption. In modern ECF hardwood pulp mills the bleaching sequences (A/D-EOP-D-P or D/A-EOP-D-P) initiate with a long, hot acidic stage which a primary target is to remove most of hexenuronic acid in the pulp. Therefore, active chlorine can be consumed from the traditional 40 kg/t to the level of 20-25 kg/t. The whole bleaching sequence lasts typically 4-5 h. The nucleophilic nature of hypochlorous acid formed in situ in chlorine dioxide bleaching leads to the secondary reactions of hexenuronic acid. Indeed, the nucleophilicity of hypochlorous acid could be enhanced through formation of a highly reactive, electrophilic quaternary chloroammonium cation in the presence of a tertiary amine. After discovering a catalyst, triethylenediamine that is both an industrially used and stable enough chemical, catalytic bleaching (Hcat), utilizing hypochlorite (H), triethylenediamine (DABCO) and its derivative N-carboxymethyltriethylenediamine (CM-DABCO), has the potential to improve the chemical and energetic efficiency of bleaching processes in chemical pulp mills, e.g., through reducing the reaction time of the bleaching processes. Indeed, this thesis studied to clarify if new kraft pulp bleaching sequences with not only Hcat as the first stage (HcatZP and HcatZ/DP) but also as an initial stage of chlorine dioxide (D) and an intermediate stage of Hcat (D0EHcatP) could provide fully bleached pulps. The bleaching sequences of the studied eucalyptus pulps include HcatZP, HcatZ/DP and D0EHcatP which attained a final brightness of 88, 89, and 88% ISO, respectively. In this thesis, it was shown that the HcatZP bleached pulps had low carbonyl group content. Interestingly it was shown that cellulose is not damaged at all in the ozone stage that typically depolymerizes cellulose. In the last part of the thesis, the efficiency and stability of the applied catalysts were studied which made the CM-DABCO as the supreme catalyst. Thus, it can already be claimed that production of almost fully bleached pulp with an exceptionally efficient system is feasible. Softwood pulp bleaching technology has not undertaken major developments in comparison with hardwood pulp bleaching during the last generation. The reason is the content of hexenuronic acid in softwood pulps is relatively low which makes the use of the long, hot acid treatment uneconomic. The catalytic bleaching offers here a solution which extracts hexenuronic acid very fast without depolymerizing cellulose

Chemical characteristics and stability of eucalyptus kraft pulps bleached with tertiary amine catalyzed hypochlorous acid

We recently found that subsequent treatments of hardwood kraft pulps with a tertiary amine (DABCO; 1,4-diazabicyclo[2.2.2]octane) catalyzed hypochlorous acid (Hcat), ozone (Z) and hydrogen peroxide (P) may provide full brightness with low chemical dosages in a short overall reaction time. Here we report chemical characteristics and stability of Hcat–Z–P bleached eucalyptus kraft pulps. In comparison with a normal ECF (elementary chlorine free) bleached pulp the Hcat–Z–P bleached pulps had low carbonyl group content while the degree of polymerization of cellulose remained at high level. However, the brightness of the Hcat–Z–P bleached pulps was reversed more easily under humid ageing conditions in comparison with the ECF bleached pulp. The discoloration was accompanied by an increase in Raman emission at 1560 cm−1 which is indicative of formation of highly conjugated chromophores. The brightness reversion did not correlate with the carbonyl content that is often considered to be the main origin of the brightness loss under humid conditions. In contrast, the brightness instability of the catalytically bleached pulps possibly resulted from the relatively high organochlorine content.Peer reviewe

Articular Cartilage Assessment Using Ultrashort Echo Time MRI: A Review

Articular cartilage is a major component of the human knee joint which may be affected by a variety of degenerative mechanisms associated with joint pathologies and/or the aging process. Ultrashort echo time (UTE) sequences with a TE less than 100 µs are capable of detecting signals from both fast- and slow-relaxing water protons in cartilage. This allows comprehensive evaluation of all the cartilage layers, especially for the short T2 layers which include the deep and calcified zones. Several ultrashort echo time (UTE) techniques have recently been developed for both morphological imaging and quantitative cartilage assessment. This review article summarizes the current catalog techniques based on UTE Magnetic Resonance Imaging (MRI) that have been utilized for such purposes in the human knee joint, such as T1, T2∗ , T1ρ, magnetization transfer (MT), double echo steady state (DESS), quantitative susceptibility mapping (QSM) and inversion recovery (IR). The contrast mechanisms as well as the advantages and disadvantages of these techniques are discussed

The investigation of rheological and strength properties of NFC hydrogels and aerogels from hardwood pulp by short catalytic bleaching (Hcat)

International audienceAlkaline washed nanofibrillated cellulose (NFC) was obtained via TEMPO-mediation of hardwood pulp which had been short catalytically bleached (Hcat) under a controlled range of conditions. With careful combination of bleaching conditions, together with the subsequent alkali pre-treatment prior to TEMPO oxidation, it is possible to reduce xylan content of Hcat hardwood birch pulps as compared to traditional elemental chlorine free (ECF) bleaching. The defined amount of xylan is seen to affect the static water-holding and agglomeration state of the respective NFC. It is shown that colloidal interactions between the nanofibrils are dependent on the amount of water present in the NFC hydrogels as water retained within xylan induced swelling of the fibrils that resulted in a weaker aerogel structure