Samyn Pieter, Cosemans Patrick
Department of Innovations in Circular Economy and Renewable Materials, SIRRIS, 3001 Leuven, Belgium.
Polymers (Basel). 2024 Apr 14;16(8):1095. doi: 10.3390/polym16081095.
While adding different micro- and nanocellulose types into epoxy coating formulations with waterborne phenalkamine crosslinker, effects on processing conditions and coating performance were systematically investigated. The variations in viscosity, thermal and thermomechanical properties, mechanical behavior, abrasive wear, water contact angles, and coating morphologies were evaluated. The selected additives include microcrystalline cellulose (MCC) at 1 to 10 wt.% and cellulose nanocrystals (CNC), cellulose nanofibers (CNF), cellulose microfibers (CMF), and hydrophobically modified cellulose microfibers (mCMF) at 0.1 to 1.5 wt.%. The viscosity profiles are determined by the inherent additive characteristics with strong shear thinning effects for epoxy/CNF, while the epoxy/mCMF provides lower viscosity and better matrix compatibility owing to the lubrication of encapsulated wax. The crosslinking of epoxy/CNF is favored and postponed for epoxy/(CNC, CMF, mCMF), as the stronger interactions between epoxy and CNF are confirmed by an increase in the glass transition temperature and reduction in the dampening factor. The mechanical properties indicate the highest hardness and impact strength for epoxy/CNF resulting in the lowest abrasion wear rates, but ductility enhances and wear rates mostly reduce for epoxy/mCMF together with hydrophobic protection. In addition, the mechanical reinforcement owing to the specific organization of a nanocellulose network at percolation threshold concentrations of 0.75 wt.% is confirmed by microscopic analysis: the latter results in a 2.6 °C (CNF) or 1.6 °C (CNC) increase in the glass transition temperature, 50% (CNF) or 20% (CNC) increase in the E modulus, 37% (CNF) or 32% (CNC) increase in hardness, and 58% (CNF) or 33% (CNC) lower abrasive wear compared to neat epoxy, while higher concentrations up to 1.5 wt.% mCMF can be added. This research significantly demonstrates that nanocellulose is directly compatible with a waterborne phenalkamine crosslinker and actively contributes to the crosslinking of waterborne epoxy coatings, changing the intrinsic glass transition temperatures and hardness properties, to which mechanical coating performance directly relates.
在将不同类型的微纤维素和纳米纤维素添加到含有水性酚醛胺交联剂的环氧涂料配方中时，系统地研究了其对加工条件和涂层性能的影响。评估了粘度、热性能和热机械性能、力学行为、磨料磨损、水接触角和涂层形态的变化。所选添加剂包括1至10 wt.%的微晶纤维素（MCC）以及0.1至1.5 wt.%的纤维素纳米晶体（CNC）、纤维素纳米纤维（CNF）、纤维素微纤维（CMF）和疏水改性纤维素微纤维（mCMF）。粘度曲线由添加剂的固有特性决定，环氧/CNF具有很强的剪切变稀效应，而环氧/mCMF由于封装蜡的润滑作用提供了较低的粘度和更好的基体相容性。环氧/CNF的交联受到促进，而环氧/（CNC、CMF、mCMF）的交联则被推迟，因为环氧与CNF之间更强的相互作用通过玻璃化转变温度的升高和阻尼因子的降低得到证实。力学性能表明环氧/CNF具有最高的硬度和冲击强度，导致磨损率最低，但环氧/mCMF的延展性增强且磨损率大多降低，同时具有疏水保护作用。此外，通过微观分析证实，在0.75 wt.%的渗滤阈值浓度下，由于纳米纤维素网络的特定组织而产生的机械增强作用：与纯环氧相比，玻璃化转变温度升高2.6℃（CNF）或1.6℃（CNC），弹性模量增加50%（CNF）或20%（CNC），硬度增加37%（CNF）或32%（CNC），磨料磨损降低58%（CNF）或33%（CNC），而可以添加高达1.5 wt.%的mCMF更高浓度。这项研究显著表明，纳米纤维素与水性酚醛胺交联剂直接相容，并积极促进水性环氧涂料的交联，改变了固有玻璃化转变温度和硬度性能，而涂层的机械性能直接与之相关。
