Differences In Adsorption Behavior Of Cationic Amylose And Amylopectin And Their Effects On Paper Enhancement

To save wood fiber raw materials,protect the environment and save energy,the recycling and utilization of waste paper fiber is of great significance.However,after recycling,the strength properties of secondary fibres will not meet the demand,which severely limits their using in paper products.Therefore,paper reinforcement is often added in the paper industry to improve the strength properties of the finished paper.Therefore,paper reinforcement is often added in the paper industry to improve the strength properties of the paper.Cationic starch is a functional starch derivative whose cationic groups and large number of hydroxyl groups in the molecular chain make it an excellent additive for use in the wet end of paper to improve paper strength.It has been shown that the proportion of amylose(AM)and amylopectin(AP)in the starch and the structural differences between the two influence the enhancement of the strength properties of the paper.In other words,there should be a difference in the adsorption of AM and AP on cellulose.At present,there are no systematic studies and clear conclusions on the influence of structural differences between single starch components(i.e.AM and AP)on their adsorption behavior on cellulose and their effect on paper strength enhancement,and the effects of factors such as degree of substitution(DS),p H and ionic strength have yet to be investigated.In this study,AM and AP were isolated and purified from corn starch and modified by etherification to obtain quaternised amylose(QAM)and amylopectin(QAP)with a range of substitution degrees respectively;then,the adsorption behaviour of QAM and QAP on the fibre surface and the viscoelastic properties of the adsorbed layer were investigated using the quartz crystal microbalance(QCM),and their enhancement of the fibre network strength was investigated to reveal the structure-adsorption-efficiency relationship between the two at the molecular level.Finally,the enhancement effects of different ratios of QAM and QAP on paper were also studied to provide theoretical guidance for the selection of suitable starch in the wet end of paper production.The details of the study and the results are as follows:(1)Isolation and purification of AM and AP and quaternised modification.In this study,AM and AP were isolated and purified from corn starch,and their purity and molecular weight were tested.The purity of AM was 92.4%±1.5%,and the molecular weight was 3.72×10~4Da;the purity of AP was 95.3%±1.6%,and the molecular weight was 2.03×10~6 Da.The results showed that the isolated AM and AP were of high purity and representative and could be used for subsequent experimental studies.Then the separated AM and AP were used as raw materials,and the AM and AP were activated using sodium hydroxide at 65℃,then reacted with the cationic etherizing agent3-chloro-2-hydroxypropyltrimethylammonium chloride.A series of QAMs and QAPs with different degrees of substitution(DS)were obtained by changing the reaction time,the amount of base and the etherizing agent.Various characterization methods were used to determine the results and properties of QAMs and QAPs.(2)Enhancement effect of QAMs and QAPs with different DS on paper and their adsorption behaviors on charged surfaces.The adsorption behavior of QAM(DS=0.15 and 0.41)and QAP(DS=0.20 and 0.40)on cellulose nanofibers(CNF)and the viscoelastic properties of the adsorbed layer were investigated using the QCM-D technique,and the effects of structural differences,charge density,p H,ionic strength and charged substrate on their adsorption behavior were investigated.QAM and QAP were added as additives to the pulp suspension at different conductivities,and the three performance indexes of tensile index,burst index and tear index of the paper were measured.The results showed that the effect of DS size on the adsorption behavior of QAMs on the CNF interface was more obvious,as the adsorption layer of QAMs with high DS was thinner and stiffer with flatter conformation,while the adsorption layer of QAMs with low DS was thicker and softer with relatively curled conformation.The effect of DS on the conformation of QAP adsorption layer was less.The higher the p H,the significantly higher the adsorption of QAM,the more rigid the QAM adsorption layer at the same adsorption amount,and the easier QAM adsorption within the CNF membrane.And the effect of p H on QAP adsorption was smaller,which may be related to the conformation of QAP.The ionic strength of the environment also affects the adsorption of QAMs and QAPs on cellulose.With increasing ionic strength,the adsorption of QAM on cellulose decreased,especially theΔF of QAM-0.15 with low charge density decreased from-48.5 Hz to about-3.6 Hz.In contrast,QAM-0.15 with high charge density had a thicker and softer adsorption layer and a more curled conformation,although the adsorption amount decreased.The effect of ionic strength on QAPs was less pronounced than that of QAMs,with a decrease in adsorption for QAP-0.20 and a slight increase in adsorption for QAP-0.40,which had little effect on the conformation of the adsorbed layer.For charged substrates,the adsorption of QAM on cellulose interface was always higher than that on the silica interface,regardless of the DS level,because the interlayer pores of CNF after enough wetting up were larger and the molecular weight of QAM is relatively small,which can easily enter the interior of the CNF membrane.The effect of charged substrates on the adsorption behavior of QAP was not significant compared to the adsorption behavior of QAM on charged substrates.The charged substrate had little effect on the conformation of QAP adsorption layer,and QAP with higher molecular weight could not enter into the interior of CNF membrane.For the paper enhancement effect,QAM with high DS was better than QAM with low DS,while QAP with low DS than QAP with high DS.The effect of the magnitude of the medium conductivity on the enhancement of paper by cationic additives was consistent with the adsorption results.Except for QAP-0.40,the high conductivity of the media had a detrimental effect on the performance enhancement of the cationic additive on the paper in the wet end of paper.(3)The enhancement effect of different ratios of QAM and QAP on paper.Five different ratios(QAM:QAP=1:9,1.5:8.5,2:8,2.5:7.5,3:7)of similar substitution of QAM and QAP(DS about 0.04,0.08,0.20,0.40,respectively)were compounded and added to the paper suspension as reinforcing additives,and tensile index,burst index and tear index of paper were determined.It was found that the QAM-QAP additive blend with a substitution degree of 0.08 was able to enhance the strength properties of the paper better while meeting the low substitution degree,i.e.,low cost,and the best enhancement of the strength properties of the paper was achieved at a ratio of 2:8between QAM and QAP.The emission scanning electron microscopy visualizes the action of QAM and QAP between the fibers,both distributed on the fiber surface and between the fibers,resulting in a stronger bond between the fibers and effectively enhancing the strength properties of the paper.In conclusion,this study provides a theoretical basis for the wet end application and raw material selection of starch in papermaking.