基于共预絮凝在线改性的烷基烯酮二聚体对纸张纤维的疏水作用 — 碳酸钙填料粒子表面竞争性吸附的协同调控

The cultural paper used for writing, printing and etc. must endow an appropriate hydrophobicity, efficiently retaining the sizing agent - alkyl ketene dimer (AKD) on the pulp fibers is a key technology. Based on the low sizing efficiency of AKD in paper products, the project intents to create the technology system of online multiple components co-preflocculation, papermaking wet end additives like retention aids and strength enhancer were incorporated into a more controlled pretreatment unit, to improve the retention of AKD on fibers, and to regulate precisely the competitive adsorption of precipitated calcium carbonate (PCC) filler particles for AKD. Firstly, AKD flocs will be obtained by the pretreatment, and their microstructure and chemical properties will be characterized. The surface chemical nature of PCC will be discussed, the adsorption kinetics of AKD on PCC will be obtained, and the synergetic effect on inhibiting adsorption of PCC will be explored. The relationships between the retention of AKD on fibers, the adsorption of AKD on PCC, and the sizing and reversion will be studied, and the bonding mechanism of AKD on paper fibers will be clarified. This project will resolve the problems in low sizing efficiency of AKD, and the conflict in PCC filling and AKD sizing, and provide the foundation of theory and technology of paper sizing.

用于书写、印刷等文化纸必须具有适当的疏水性，施胶剂—烷基烯酮二聚体（AKD）在纸浆纤维上的高效留着是其技术关键。本项目基于目前AKD施胶效率低的现状，建立多元组分共预絮凝在线改性技术创新体系，在一个反应条件更可控的预处理单元，利用造纸湿部助剂如助留剂、增强剂等对AKD及PCC产生预絮凝作用，提高AKD微粒在纤维上的留着几率，并协同精准调控沉淀碳酸钙（PCC）填料粒子对AKD的竞争性吸附。考察共预絮凝条件对AKD凝聚体的微观结构与化学性质的影响，阐明AKD凝聚体的形成规律；考察共预絮凝参数对PCC颗粒表面化学特性的影响，阐明PCC对AKD的吸附动力学，揭示共预絮凝对PCC吸附特性的协同调控机制；综合研究AKD留着率、PCC对AKD的吸附量与纸张施胶度及施胶逆转的关系，明晰AKD与纤维的键合机制。本研究可解决AKD施胶效率低，PCC加填与AKD施胶冲突的难题，为纸张施胶技术及理论发展奠定基础。

本课题围绕造纸系统中碳酸钙加填导致AKD施胶效率低的问题展开研究，利用湿部多元助剂共预絮凝技术，通过形成絮凝体来改变AKD及PCC的微粒形态及表面荷电性质，从而提高AKD的留着率，协同抑制PCC颗粒对AKD的吸附，增大AKD与浆料纤维的反应几率，达到提高施胶效率的目标。.首先，探讨了预絮凝对造纸湿部组分包括：纤维、填料、多元助留剂、增强剂等与AKD的相互作用调控。结果表明，造纸湿部系统对AKD的吸附能力与最终纸张的施胶度有着紧密的联系。碳酸钙填料与纤维对AKD存在竞争性吸附，填料比纤维具有对AKD更强的结合能力，并且所结合的AKD会对纸张施胶度产生负贡献。当AKD与纤维的反应时间为2.5分钟时，纸张施胶度最高，对应的系统对AKD的吸附量也达到最高，且在此时间内AKD未发生明显的水解。其次，在合适的反应顺序下，传统助留剂及增强剂能够絮凝AKD及PCC成一定体积的絮凝体，并降低两种微粒表面负电性，提高各自与纤维的结合能力，同时增大AKD与PCC的斥力，有效减少PCC对AKD的不良吸附。采用一元至多元助剂包括CPAM/CS/皂土对AKD及PCC进行预絮凝处理，结果表明，CPAM分子量增加可增大絮凝体的尺寸，电荷密度增加则使絮凝体的尺寸减小。预絮凝使PCC填料粒径增大8-9倍，BET比表面积降低约50%，Zeta电位从负电转变为正电性，因此对AKD的吸附能力从11mg/g下降约4mg/g。利用皂土/CS/CPAM共预絮凝AKD及PCC，使纸张cobb值从32.2降低到20.15，填料留着率达到90.51%，施胶度从117.2增大到134.8，纸张抗水稳定性明显提高。且纸张存放40天后未产生明显的施胶逆转。此外，与传统工艺相比，预絮凝施胶的纸张强度性能显著提高，光学性能相当，纸张匀度更好。.本研究结论为解决AKD施胶效率低，PCC加填与AKD施胶冲突的难题，为纸张施胶技术及理论发展奠定基础。