Poly(N-Isopropylacrylamide-Co-Methacrylic Acid) Micro/Nanoparticles: Formulation, Size Distribution and Use for Cu⁺⁺ Adsorption

Poly(N-isopropylacrylamide-co-methacrylic Acid (PNIPAAm-MAA) micro/nano-particles were formulated. The effect of monomer ratio, surfactant, and crosslinker contents on size/size distribution, phase transition behavior, and Cu²⁺ adsorption efficiency of the particles was investigated. The ionized MAA groups brought both temperature and pH sensitiveness to the PNIPAAm-MAA copolymer particles. As monomer ratio and crosslinker content increased and the amount of surfactants decreased, the particle size increased. The influence of the crosslinker content on particle size was less significant compared to the effect of monomer ratio and surfactants. When temperature increased, the particles tended to shrink and reduced their size to near or below 100nm. The Weibull distribution was successfully used to describe the diameter distribution of the nano-particles, whereas the lognormal was deemed not adequate for that purpose. The method of moments was used to predict parameters of the Weibull distribution. The Weibull parameters were recovered from diameter mean and variance, both of which were predicted from temperature. The distributions predicted from various temperatures for MAA/NIPAAm ratios of 0.05 and 0.10 showed trends similar to those in the data. Studies on chelation efficiency of the particles with Cu²⁺ ions showed that the amount of the Cu²⁺ ions adsorbed varied with temperature. Particle size played a very important role in the adsorption and nanoparticles greatly improved adsorption efficiency, compared with their micro hydrogel counterparts. The amount of adsorption increased with increase of MAA ratio in copolymers, but adsorption efficiency decreased with increased particle size. The high adsorption efficiency of metal ions by PNIPAAm-MAA polymer particles provides an effective technique for recovering metal ions (e.g., Cu²⁺) from wood treated with metal based preservatives.