Shu Hui Wang

HTPB‐based polyurethanes. II. SINs with PMMA

Simultaneous interpenetrating networks from poly(methyl methacrylate-co-ethyleneglycol dimethacrylate) (PA) and a hydroxyl-terminated polybutadiene-based polyurethane (PU) were prepared with various hard-segment contents (X) in the PU and different ratios (PU/PA) between the components. The level of the reinforcement, the mechanism of molecular failure, and the phase inversion depended strongly on X. Dynamic mechanical results indicated that the interpenetration occurred in the rigid blocks of the PU. The improved thermal and mechanical properties observed with higher values of X were interpreted in terms of the molecular weight and polydispersity of the hard blocks in the PU.

Nanocomposite Microcapsules from Powders of Polyhydroxybutyrate (PHB) and Smectite Clays

Drug delivery systems involving microcapsules provide an attractive way to improve the performance of many chemical and biological substances. These systems may be used for several industrial segments, especially medical, pharmaceuticals and cosmetics. PHB is a polyhydroxyalkanoate available in powder form, biocompatible, biodegradable and inert towards animal tissues. The obtained PHB/smectite clay nanocomposite improved the physical-chemical properties of PHB, including its biodegradability. In this work, we describe the preparation of microcapsules from two nanocomposites systems: a) PHB and Cloisite 20A organoclay (PHB1) and b) PHB and natural Brazilian green policationic clay (PHB2). When analyzed by XRD, the films and microcapsules did not show a d(001) peak, demonstrating an exfoliated structure for the nanocomposites. The films have shown by SEM an homogeneous distribution with the clay mineral particles spread homogeneously by the PHB film. The new microcapsules/nanocomposites showed an “hydrangea” morphology. The diameter of the microcapsules was variable between 0.5-15 µm.

Morphology and Damping Behavior of Polyurethane/PMMA Simultaneous Interpenetrating Networks

A series of polyurethane/PMMA simultaneous interpenetrating networks (SINs) with various hard segment contents (X) in the polyurethane phase (X = 15.5 to 36.5% in polyurethane) and wide range of polyurethane (PU) to polyacrylate (PA) ratio (PU/PA = 20:80 to 80:20) were prepared, and the damping and mechanical properties of these materials were studied. The damping of polyurethane soft phase was increased and shifted to lower temperature with increased content of PA vitreous phase. The mechanical properties were improved with increasing PA contents. The results show that PA and the polyurethane hard segment interaction play a special role in chain interpenetration density and its magnitude is revealed by the decreased dispersed domain size observed by scanning electron microscopy (SEM) and increased loss area as measured by dynamic mechanical thermal analysis (DMTA). When the weight ratio of PU/PA was 40:60, the resulting SIN materials possessed better damping properties, independent of X concentration.

Evaluation of Urea Encapsulation by Microcapsules of PHB/MMT and PHB/OMMT Nanocomposites

Urea is the most used nitrogen fertilizer around the world being responsible for many environmental problems. Preparation of microcapsules from biodegradable polymer has been reported as a main system to sustain active substances, finding application in different areas. The objective of this work was to sustain urea in nanocomposite microcapsules of poly(3-hidroxybutyrate) (PHB) reinforced with a smectite Brazilian clay in its natural (MMT) and modified (OMMT) form. PHB/MMT and PHB/OMMT microcapsules were obtained by w/o/w emulsion. Characterization were performed by XRD and optical microscopy. Structural and morphological differences observed by XRD and optical microscopy shown that PHB/OMMT microcapsules are smaller than PHB/MMT microcapsules, with average size diameter ranging ~ 49 µm. Results indicate that PHB/OMMT microcapsules present more defects and fractures than PHB/MMT microcapsules.

Preparation and Characterization of Microcapsules from PBSL/VMF2 Nanocomposite

In this work, nanocomposite films and microcapsules were prepared from a dispersion of poly(butylene succinate-co-lactate) (PBSL) and Brazilian clay (VMF2). A nanocomposite precursor solution was prepared by adding, under mechanic stirring, a solution of PBSL-5% to a dispersion of VMF2–0. 8% in chloroform. Nanocomposite films were prepared by casting 10 mL of the nanocomposite precursor onto glass Petri dishes, then left overnight for solvent evaporation before drying in a vacuum oven. Microcapsules were obtained from the nanocomposite precursor by solvent diffusion method. PBSL and PBSL/VMF2 films and microcapsules thus prepared were characterized by optical microscopy, XRD, and SEM. XRD of VMF2 showed that this clay contains montmorillonite and kaolinite. XRD of the PSB/VMF2 nanocomposite showed intercalation of the montmorillonite, indicating that both clay minerals are finely dispersed within the polymer matrix. SEM of the microcapsules showed homogeneous spheres with particle sizes in the range 50–150 μm.

Estudo fotofísico do cromóforo p-fenóxi-metil-estilbeno livre ou ligado a um esqueleto de poliestireno

O comportamento fotofisico do cromoforo p-fenoxi-metil-estilbeno livre ou como grupamento pendente em cadeia polimerica foi estudado atraves de espectros de absorcao e fotoluminescencia em solucao e no estado solido. As caracteristicas do cromoforo livre foram observadas usando-se o composto modelo p-(p-etil-fenoximetil)estilbeno e as do cromoforo ligado a um esqueleto polimerico foram estudadas com o poli(estireno-co-estilbenil-p-metoxiestireno). Os resultados sao interpretados em termos de emissoes provenientes do cromoforo isolado ou de agregados formados no estado fundamental