Abstract
Preparation of polymer microspheres from naturally occurring resource is a challenge. Here, a rosin-based polyol (RAG) was used to prepare polyurethane resin (RPU) firstly, and then act as both self-assembled precursor and emulsifier, rosin based polyurethane microspheres (RPUMs) were prepared. In the process of self-emulsification, the RPU formed vesicles by self-assembly. The outer shell of the vesicle consisted of hydrophilic segments, while the inner shell contained the hydrophobic phase. After cross-linking the RPU and removal of the solvent in the core, the porous-hollow microspheres with pH-sensitive were obtained. The microspheres were characterized by optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The effect of type and amount of the hydrophilic chain extender, and solvent on the morphology, particle size and distribution, and buffer volume of the microspheres were determined. The best conditions for synthetic RPUMs were as follows: nNCO/nOH = 1, nRAG:n1-(2-hydroxyethyl) piperazine = 4:6, with azodiisobutyronitrile level of 1.0 wt.%, based on reactive monomers, mixing speed of both emulsification and polymerization at 400 r·min−1, the RPUMs synthesized had porous-hollow structure with a buffer volume of 1.6 mL.
Highlights
In recent years, research on green renewable energy has become a global hot spot due to fossil fuel depletion and environmental pollution [1]
Where V1 is the NaOH consumption volume corresponding to the first mutation point, V2 is the NaOH consumption volume corresponding to the second mutation point; [basic], [OH− ] and [H+ ] are the molar concentrations of the added NaOH for titration, free hydroxide ion and hydrogen ion, respectively, and CNH is the total molar concentration of the amino groups in rosin based polyurethane microspheres (RPUMs)
3.1 Effect of Hydrophilic Chain Extenders on the Properties of Microspheres When the porogen was fixed as toluene, with the solid content of rosin-based PU (RPU) of 25%, nRAG:nchain extender = 4:6, stirring speed for both polymerization and emulsification were 400 r·min-1 and reaction temperature at 80°C, different types of hydrophilic chain extender (Fig. 1) were used to prepare the RPUMs, and their effects on the particle size, particle distribution index (PDI), and dissociative parameters of the RPUMs are shown in Tables 1 and 2, the optical microscope photographs and pH sensitivity of the RPUMs are presented in Figs. 2 and 3, respectively
Summary
Research on green renewable energy has become a global hot spot due to fossil fuel depletion and environmental pollution [1]. Polyurethanes (PUs) have been widely used in rigid foams [4], elastomers [5], adhesive [6], coatings [7] and biomaterials [8] due to their unique performance and various morphological structures Among these morphologies studied, porous-hollow PU microspheres have recently aroused considerable interests. Previous studies has proved that porous-hollow microcapsules or microspheres show great potential for applications in the fields of adsorbents [9], tissues engineering [10], drug diagnosis [11], environmental protection [12], etc., owing to their high specific area, good flow ability and surface permeability. In order to widen the application field of RPU and improve the added value of rosin, a new type of functional PU based on rosin was developed. After cross-linking the RPU and removal of the solvent in the core, the porous-hollow microspheres with pH-sensitive are obtained
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