Core-Shell Morphology of Redispersible Powders in Polymer-Cement Waterproof Mortars

Abstract

Redispersible powders based on soft core-hard shell polymer particles can be used as additives in polymer-cement mortars. The role of this morphology on the spray-drying production of these powders and on the crack-bridging properties of the corresponding cement-based membranes is investigated. Different polymer latexes at high solid content with varied core-shell ratio, shell thickness and chemical composition (hardness) were prepared from styrene and 2-ethylhexyl acrylate monomers via semi-batch emulsion polymerization. The latexes were characterized in terms of size, composition, and glass transition temperature (T g ), and spray-dried to obtain redispersible polymer powders (RPPs) using poly (vinyl alcohol) and limestone powder as anti-caking agents. The polymer powders were mixed with a mortar mixture and redispersed in water to produce cement-based membranes, which were tested for crack-bridging properties at different temperatures. The results showed that it was not possible to spray-dry a dispersion of homogeneous polymer particles with T g of −25 ∘ C, unless these particles are protected by much harder (high T g ) shell. In particular, it was observed that a thicker shell improved the spray-ability, but lowered the crack-bridging properties of the produced membrane. A trade-off between these two was revealed to be the key for the optimal design of the polymer nanoparticles, as proven by the systematic study of the core-shell morphology reported in this work. The best compromise was shown to consist of particles larger than 300 nm, shell thickness of about 5 nm, and core-shell ratio of 97%, with styrene content in the shell not larger than 80% to avoid excessive hydrophobicity.

The Relationships between the Working Fluids, Process Characteristics and Products from the Modified Coaxial Electrospinning of Zein

“…It has proven to be possible to perform the electrospinning process even when one or more of the working fluids cannot on its own be processed: For instance, in modified coaxial electrospinning, a spinnable core solution is partnered with an unspinnable sheath fluid. These novel processes permit the production of nanofibers with increasingly complicated nanostructures [32,33,34,35,36,37]. As a result, in the literature, there are numerous publications that explore the influence of a single parameter on the nanofibers or nanostructures prepared by electrospinning, elucidating relationships for manipulating the products (mainly in terms of diameter, but also for other properties such as morphology, surface smoothness and the details of the nanostructure) [38,39,40,41,42,43].…”

Redispersible Polymer Powders with High Bio‐Based Content from Core–Shell Nanoparticles

“…For both the systems, LA‐IB and HL‐ST, samples with different shell thickness were synthesized to find the best optimum between shell protection during drying and filming ability, taking into account a previous study that assessed 10 nm as the minimum thickness needed to properly shield the core. [ 13 ] To calculate the amount of monomer to be added for the synthesis of the shell, we relied on Equation (S5) (Supporting Information), which imposes the preservation of the number of nanoparticles. The samples produced with their main features are listed in Table 1, where the measured shell thickness has been evaluated by halving the difference between the diameters of the core–shell NPs and of the cores, both measured via DLS.…”

Design and preparation of high-performance polymer mortars based on performance prediction model

“…Polymer mortars (PMs) are new cementitious materials consisting of cement, aggregates, and polymers that may be distributed in water [7][8][9]. PMs composite materials have prominent capabilities, including high flexibility [10] and mechanical strength [11], excellent acid-based corrosion resistance [12,13] and waterproofing properties [14,15], owing to the unique network structure of the mortar. Polymers are ecofriendly [16,17] and cost-effective [18,19].…”