Refining Technology And Its Mechanism For Sack Paper

Sack paper is a very important material for goods packaging and the quality demand for sack paper is getting higher. With the development of society as well as the improvement of living conditions, refining is one of the main methods for quality improving of sack paper. Low consistency refining (LCR) is used in sack paper making in China, and few reports on it are available. High consistency refining (HCR) or HCR followed by LCR is widely used in sack paper making worldwide, and the quality of the paper is much better than that produced in China. For this reason, unbleached Masson's Pine kraft pulp and its mixed pulp with eucalyptus pulp were chosen as the raw materials for the study of the refining, technology and mechanism of HCR, LCR for sack paper. Processes of HCR, LCR, and LCR following HCR with different ratios of Masson's Pine and Eucalyptus mixed pulps were studied. The comparison of handsheets properties of different refining processes, the change of fibre surface morphology, fibre surface chemical composition and fibre surface charge were carried out. The results are as following.1. HCR had the advantage of maintaining the fibre length for 100% Masson's Pine kraft pulp. The properties of handsheets, such as the air permeability, tensile stretch, tear index and Tensile Energy Absorption (TEA) index were higher than that of LCR. And the characteristics of handsheets could meet the standard GB/T 24287-2009 in a wide range of beating degree 15-24oSR.2. The properties of handsheets, such as the tensile index and burst index were better with LCR for 100% Masson's Pine kraft pulp. The characteristics of handsheets could meet the standard GB/T 24287-2009 in a narrow range of beating degree 15-18oSR.3. The optimal parameters of HCR followed by LCR were as follows: the pulp was refined to a beating degree of 14~15 oSR with HCR, followed by LCR to a beating degree of 16~17oSR for 100% Masson's Pine kraft pulp. Under this condition, air permeability and TEA index was higher than 5.0μm/Pa·s and 2.37 J/g, respectively. The other properties of handsheets also could meet the standard requirements.4. Delatency treatment following HCR process of Masson's pine kraft pulp could improve the handsheets properties of tensile index, tear index and burst index, but decrease the air permeability, TEA index and tensile stretch.5. The appropriate beating degree was 20±2oSR by using HCR followed by LCR for sack paper with Masson's Pine kraft pulp and 15% eucalyptus kraft pulp, and the appropriate beating degree by using HCR, LCR, and HCR followed by LCR was 23±2oSR if 30% eucalyptus kraft pulps was added. The optimal beating degree increased with the increase of the ratio of eucalyptus pulp and Masson's pine pulp. The properties of the handsheets decreased with the increase of the ratio of eucalyptus pulp.6. The properties of handsheets, such as the tensile index and burst index were better with LCR for Masson's pine and eucalyptus mixed pulps, and the tensile stretch, tear index and air permeability were better with HCR. HCR followed by LCR had the advantages of both HCR and LCR.7. Fibre surface charge of refined pulp increased as beating degree increased. A linear relationship was obtained between surface charge and beating degree. The surface charge of LCR fibres was higher than that of HCR at the same beating degree.8. There were more acidic groups concentrating on the fibre surface with LCR for 100% Masson's pine kraft pulp, and greater degree of fibre-fibre bonding could be obtained due to the swelling fibre and the higher contact areas between fibres. It meant that, tensile index and burst index were better with LCR, but the air permeability, which is very important for sack paper, was poor.The refining processes were optimized and it's mechanism of Masson's kraft pulp and its mixed pulps with eueucalyptus kraft pulp for sack paper was studied which offered a guidance for sack paper producing and studying.