Aversa Raffaella, Ricciotti Laura, Perrotta Valeria, Apicella Antonio
Advanced Materials Laboratory, Department of Architecture and Industrial Design, University of Campania, Via San Lorenzo, 81031 Aversa, Italy.
Polymers (Basel). 2023 Sep 28;15(19):3922. doi: 10.3390/polym15193922.
Although geopolymers, as structural materials, should have superior engineering properties than traditional cementitious materials, they often need to improve their final characteristics' reproducibility due to the need for more control of the complex silico-aluminate decomposition and polymerisation stages. Thermosetting of a reactive geopolymeric paste involves tetrahedral Silicate and Aluminate precursor condensation into polyfunctional oligomers of progressively higher molecular weight, transforming the initial liquid into a gel and a structural solid. Viscosity and gelation control become particularly critical when the geopolymer is processed with 3D printing additive technology. Its physical state modification kinetics should match the flow and setting characteristics required by the deposition process. The reaction kinetics and the elastic and viscous characteristics preceding gelation and hardening have been investigated for an alkali-activated Metakaolin/Sodium Silicate-Sodium Hydroxide paste with a Si/Al ratio > 3. A chemoreological approach has been extended to these inorganic polymerisable systems, as already utilised for organic thermosetting polymers. Differential scanning calorimetry and Oscillatory DMA were carried out to monitor the advancement of the polymerisation reaction and the associated variations of the rheological viscoelastic properties. Dynamic thermal scans were run at 1 °C/min and a frequency of 10 Hz for the dynamic mechanical tests. The observed kinetics of polymerisation and variations of the elastic and viscous components of the complex viscosities and shear moduli are described in terms of polycondensation of linear and branched chains of oligomeric macromolecules of increasing complexity and molecular weight up to gelation (Gel1) and cross-linking of the gelled macrostructure (Gel2) and final glassy state. Geopolymerization can be allocated into two main behavioural zones: a viscoelastic liquid paste below 32.5% of reaction advancement and a viscoelastic solid above. Initial complex viscosities range from 2.3 ± 0.9 × 10 MPas to 6.8 ± 0.9 × 10 in the liquid-like state and from 1.9 ± 0.1 MPa to 9.6 ± 2.1 × 10 MPa in the solid-like state.
尽管地质聚合物作为结构材料应具有比传统胶凝材料更优异的工程性能，但由于需要更多地控制复杂的硅铝酸盐分解和聚合阶段，它们往往需要提高其最终性能的可重复性。活性地质聚合物浆料的热固化涉及四面体硅酸盐和铝酸盐前体缩合形成分子量逐渐增大的多官能低聚物，将初始液体转变为凝胶和结构固体。当地质聚合物采用3D打印添加剂技术加工时，粘度和凝胶化控制变得尤为关键。其物理状态改性动力学应与沉积过程所需的流动和凝固特性相匹配。对于硅铝比>3的碱激发偏高岭土/硅酸钠-氢氧化钠浆料，研究了其反应动力学以及凝胶化和硬化之前的弹性和粘性特性。一种化学流变学方法已扩展到这些无机可聚合体系，就像已用于有机热固性聚合物那样。进行差示扫描量热法和振荡动态热机械分析以监测聚合反应的进程以及相关的流变粘弹性性能变化。动态热扫描以1℃/min的速率进行，动态力学测试的频率为10Hz。观察到的聚合动力学以及复数粘度和剪切模量的弹性和粘性组分的变化，是根据寡聚大分子的线性和支链的缩聚来描述的，这些大分子的复杂性和分子量不断增加，直至凝胶化（Gel1）以及凝胶化宏观结构的交联（Gel2）和最终玻璃态。地质聚合可分为两个主要行为区：反应进程低于32.5%时为粘弹性液体浆料，高于此值时为粘弹性固体。初始复数粘度在类液体状态下范围为2.3±0.9×10毫帕秒至6.8±0.9×10毫帕秒，在类固体状态下为1.9±0.1兆帕至9.6±2.1×10兆帕。
