Enhanced Dry and Wet Web Runnability by Spray Application of Different Polymers Laboratory and Pilot Scale Studies

Transcription

1 Enhanced Dry and Wet Web Runnability by Spray Application of Different Polymers Laboratory and Pilot Scale Studies Event: EFPRO-CEPI early stage researchers workshop 2012 VTT: Kristian Salminen, Janne Kataja-aho, Elias Retulainen & Timo Rantanen Åbo Akademi: Hanna Lindqvist & Anna Sundberg

2 2 Background: Wet web properties and paper machine runnability Paper machines have reached their practical maximum width (~11 m). To increase production, higher speed and less downtime is required Increase of production speed is often limited by mechanical properties of wet web Pakarinen et al 1995 The fact remains that paper mills do not typically add chemicals to improve mechanical properties of wet web Hokkanen 1996

3 3 Background: Interactions between fibers in the wet state Hubbe 2006 molecular segments already tend to mix with each other already at wet state, before the start of drying process. A random process of molecular motions would be expected to result in interpenetration and tangling, i.e. a three-dimensional zone of contact (Hubbe 2006)

4 4 Background: Modification of the fiber surface with polymers The dispersion of fibrils and interdiffusion between fiber surfaces can be tailored by adsorbing different polymers onto fibers Modified from Myllytie 2010 Myllytie 2010

5 5 The objective of this study was to clarify the effects of spraying some commercial polymers on mechanical properties of dry and wet paper

6 6 Methods: Spraying tests at laboratory Preparation of samples Wet pressing Measurements 50 kpa 350 kpa CMC Chitosan Starch guar gum

7 7 Methods: Why to add polymers by spraying? Higher retention of polymers (with no cationic charge) No effect on formation To avoid adsorption of polymers mainly to fines fraction

8 Wet web tensile strength[ kn/m ] 10/8/ Spraying of guar gum increased the wet web tensile strength significantly, the increase was dependent on MW of guar gum Reference (water spray) CMC 1 g/m2 Guar gum 1 g/m Hydrolyzed guar gum Laboratory scale tests: SW kraft pulp Guar gum +130% Dryness [ % ] Cationic starch 1 g/m2 Chitosan 1 g/m2 Hyd. guar gum 1 g/m2 Reference CMC Chitosan Cationic starch

9 Increase in wet web strength [ % ] 10/8/ Spraying of guar gum was a significantly more efficient (6 times) way to improve the wet web tensile strength than addition of guar gum to pulp suspension Spray addition Addition to pulp suspension Guar gum addition [ % ] Laboratory scale tests: SW kraft pulp

10 10 CTMP furnish for board mid-ply Running speed 300 m/min Pilot trials with CTMP furnish Chemical addition by spraying HiVac MB suction MB Imut Kuormitus- Load lists 2 Listat Vacuum flatboxes Tasoimulaatikot Forming Rintapöytä board

11 Web dryness after former section [ % ] Wet web tensile strength [ kn/m ] 10/8/ Spraying of guar gum had little effect on dryness after former or press section Addition of cationic starch to pulp suspension decreased, while addition of guar gum increased the wet web tensile strength at a given dryness level Ref 10 kg/t 20 kg/t 1 kg/t 3 kg/t Starch 10 kg/t Starch 20 kg/t Reference Guar Gum 0.1 g/m2 Guar Gum 0.3 g/m Nip load 1000 kn/m 0.05 Nip load 500 kn/m Dryness [ % ] 50 Pilot trials: CTMP (board mid-ply)

12 Internal bond strength [ J/m 2 ] Bulk [ cm 3 /g ] 10/8/ Addition of 20% guar gum of the corresponding amount of cationic starch was needed to obtain similar increase in int. bond strength Ref kg/t kg/t kg/t kg/t kg/t Pilot trials: CTMP (board mid-ply)

13 13 Summary Adding cationic starch improved strength properties of dry paper, but had no positive effects on wet web strength Spraying of non-ionic guar gum appeared to be an interesting possibility to improve strength properties of wet paper The increase in wet web tensile strength with guar gum was higher for chemical pulp than for chemimechanical pulp Spraying of guar gum on former section had no effect on dryness after the former or press section Guar gum spraying improved internal bond strength of CTMP furnish interesting also for board manufacturing

14 Thank you for your attention!!! 10/8/ The support of Kemira, Metso Paper, Stora Enso, UPM and TEKES to this study is gratefully acknowledged