Study On The Application Of Modified Hemicellulose As Binder In Paper Coating

Norway spruce galactoglucomannans(GGMs)in low and high acetylation were investigated as a co-binder in pigmented coatings for partly substituting synthetic polymer latex.The molecular weight of GGM and acetylated GGMs were measured by HPSEC,methanolysis was conducted to analyze the sugar contents by HPLC and thermal properties tested by DSC.Acetylated GGMs were mixed with calcium carbonate mineral pigment and styrene-butadiene latex as coating color,and the mixture was cast to films.The strength properties of the films were characterized with mechanical testing,and the microstructure of binding was observed by scanning electron microscopy.Then the coating color containing Starch/GGM/acetylated GGM was prepared according to the general recipe in paper coating industry.Mechanical properties were tested by Instron,surface morphology was observed by SEM.Finally,all the natural polysaccharides were coated directly on the surface of basic paper.The mechanical properties,optical properties,air permeability,surface strength and oil resistance ability were tested.This research is leading to the further application of hemicellulose in paper coating.The main results of this thesis are in the following:1.The high acetylation was water-insoluble,so it could not be employed as binder in coating color.The addition of GGM and acetylated GGMs increased the tensile strength of films,but the strain at break dropped significantly.Compared to starch,the low acetylation GGM improved the tensile strength and the Young’s Modulus more,but lowered the strain at break.The low acetylation GGM resulted in higher tensile strength and strain at break than the native GGM.It is interesting that GGMs,despite their low molecular weight and low degree of polymerization,showed some binding abilities in pigmented coatings,which could be useful for partial substitution of styrene-butadiene latex binder.The curves obtained from Instron indicated the mechanical properties the coating color films containing starch and acetylated GGM were stable,however the one of GGM was quite normal.2.When the coating color was coated on the basic paper and the latex was the only binder in paper coating,the tensile strength,strain at break and the Young’s modulus all improved.Hemicellulose and acetylated hemicellulose did not contribute too much to the tensile strength of coated paper,but to the strain at break.The tensile strength increased firstly and then dropped with the increase of substituting hemicellulose.The replacing hemicellulose did not change the Young’s modulus,which indicating that these two natural polysaccharides could be used as binder in paper coating color.3.When the GGM and AGL solution was coated directly on the basic paper,the air permeability and the surface toughness of the raw paper are quite high.Coating of hemicellulose and acetylated hemicellulose could modify these two properties.Acetylated hemicellulose coated paper showed better air barrier ability.The SEM pictures indicated that the naked cellulose was covered fully by GGM and acetylated GGM films.Penetration dynamics analyses(PDA)demonstrates that the raw paper has very good water resistance ability,however it was lowered by coating the GGM and acetylated GGM.Both of Max and t95 decreased obviously,it could still show that the acetylated GGM had better water resistance ability the raw GGM.The mechanical properties of coated paper with GGM and acetylated GGM improved obviously,and acetylated GGM raised the tensile strength and strain at break higher than the raw GGM.4.The oil resistance of coated paper by GGM and acetylated GGM improved a lot compared with the raw paper,especially when the coating weight of acetylated GGM coated paper was 4.61 g/m~2,there was almost no oil going through into the oil-absorbing sheet.Besides,the surface strength of GGM and acetylated GGM coated paper increased.Acetylation demonstrated better surface strength.5.The glossiness of GGM and acetylated GGM improved while the whiteness dropped.The opacity did not change a lot.The whiteness of hemicellulose coated paper decreased dramatically.The conditions of acetylated hemicellulose coated paper was similar to that of hemicellulose,however the whiteness lowered less than raw hemicellulose.Acetylated showed better optical properties.