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Physical properties of urea-formaldehyde microcapsules containing an epoxy resin are presented and discussed. Microcapsules were prepared by in situ polymerization of monomers in an oil-in-water emulsion. Differential scanning calorimetry, thermogravimetric analysis, and scanning electronic microscopy were applied to investigate thermal and morphological microcapsule properties. Microencapsulation was detected by means of FTIR and Raman techniques. It was found that the amount of encapsulated epoxy resin as well as the extent of urea-formaldehyde polymerization depends on the reaction temperature and the stirring speed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

A detailed analysis of the effect of calcium carbonate nanoparticles on crystallization of isotactic polypropylene (iPP) is reported in this contribution. CaCO 3 nanoparticles with different crystal modifications (calcite and aragonite) and particle shape were added in small percentages to iPP. The nanoparticles were coated with two types of compatibilizer (either polypropylene- g -maleic anhydride copolymer, or fatty acids) to improve dispersion and adhesion with the polymer matrix. It was found that the type of coating agent used largely affects the nucleating ability of calcium carbonate towards formation of polypropylene crystals. CaCO 3 nanoparticles coated with maleated polypropylene can successfully promote nucleation of iPP crystals, whereas the addition of nanosized calcium carbonate coated with fatty acids delays crystallization of iPP, the effect being mainly ascribed to the physical state of the coating in the investigated temperature range for crystallization of iPP, as well as to possible dissolution by fatty acids of heterogeneities originally present in the polypropylene matrix.

In this work urea-formaldehyde microcapsules containing an epoxy resin are prepared by in situ polymerization of monomers in an oil-in-water emulsion. Scanning electronic microscopy (SEM) was performed to investigate on microcapsule size and surface morphology. Calorimetric and spectroscopic analyses were carried out with the aim of evaluate the encapsulation yield and the shell features. Factors determining the microencapsulability of the core material were described. In particular, our interest was devoted to a better understanding of the influence of the reaction parameters on the microcapsule properties. It was found that the encapsulation yield as well as the extent of urea-formaldehyde polymerization depends on the reaction temperature and the stirring speed.

The influence of calcium carbonate nanoparticles with different shapes (spherical and elongated) on the thermal properties and crystallization behavior of isotactic polypropylene was investigated. CaCO3 nanoparticles were covered by an appropriate coating agent to improve the interfacial adhesion between the filler and the polyolefin matrix. The nanocomposites were prepared by melt mixing and subsequent compression molding. A remarkable effect of CaCO3 on the thermal properties of iPP was observed. Moreover, the analysis of crystallization kinetics showed that CaCO3 nanopowder coated with PP-MA are efficient nucleating agents for iPP, and the overall crystallization rate results higher than plain iPP.

Four crystalline forms of isotactic poly(4-methyl-1-pentene) (i-P4MP) (forms I, II, II, and IV) have been studied through solid-state C-13 NMR CP-MAS spectroscopy. The assignment of the resonances observed in the C-13 NMR CP-MAS spectra was made by dipolar dephasing experiments. The presence in all spectra of two distinct resonances, separated by approximate to 3 ppm, of the methyl carbons indicates that the two methyls belonging to the monomeric unit are nonequivalent. This has been explained on the basis of the gamma-gauche shielding interaction and of the conformations of polymer chains and lateral groups. The resonances observed in the spectrum of form III are markedly deshielded compared to those of other forms, whereas the resonances of form I are deshielded compared to those of form IV. This deshielding has been consistently interpreted on the hypothesis that the amount of the gamma-gauche shielding effect depends on the value of the torsion angles of the main chain. Indeed, the torsion angles of the main chain for the 7/2 helical conformation of form I deviate, on average, by 12-15 degrees from the exact staggered values of 60 degrees and 180 degrees (the average values of the torsion angles are theta(1) = 72 degrees and theta(2) = 195 degrees) they deviate by 22-26 degrees for the 4/1 helical conformation of form III (theta(1) = 82 degrees and theta(2) = 206 degrees). The gamma-gauche shielding parameter, normally -5 ppm when the gauche angle is nearly 60 degrees, decreases to a value between -2 and -2.5 ppm when the torsion angle deviates by nearly 20 degrees from 60 degrees. In the form IV, the upfield shift of the resonances, compared to forms I and III indicates that the carbon atoms experience a full gamma-gauche shielding interaction and, hence, the main chain torsion angles theta(1) and theta(2) are near 60 and 180 degrees, respectively, typical of a helical 3/1 conformation. This analysis allows us to suggest that the form IV of i-P4MP is characterized by chains in 3/1 helical conformation. The resonances of the methyl carbons of the four forms of i-P4MP show narrow splittings (1-2 ppm) which should be traced back to packing effects. This has provided a chance of testing the packing model of form I and form III proposed in the literature. In the spectrum of form I, the resonance of backbone methine carbons is also split in a doublet. This splitting is due to conformational effects, rather than packing effects and confirms that, according to the refinement of the crystal structure of form I, the chains assume a helical conformation slightly distorted from the uniform 7/2 helix. The succession of torsion angles along the main chain is ...TGT'G " T " G "..., instead of (TG)(n). Therefore, backbone methine carbons of different monomeric units are conformationally nonequivalent because they experience different amounts of gamma-gauche shielding effects owing to different values of the gauche torsion angle theta(1) of different monomeric units.

Isotactic polypropylene/organoclay nanocomposites were prepared by a solution methodology and characterized by structural, morphological, and mechanical analysis. X-ray and microscopic analyses (SEM) have revealed a homogeneous dispersion of the nanoclay in the iPP matrix and good adhesion between the two phases, especially in nanocomposites containing lower organoclay amounts ( 1% and 3%). Particularly it was observed that the sample with 1% clay content maintains the exfoliated structure during processing, while the sample with 3% clay evolves from an intercalated structure toward an exfoliated structure when processed by compression molding. The influence of the modified organoclay nanoparticles on the iPP crystallization process was also investigated. The results have shown that while the nanoparticles increase the rate of crystallization there is a delay in the onset of the solidification process. A regime II-III transition temperature was also observed which decreases with increasing organoclay content. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:132–144, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20036

Poly(caprolactone) (PCL) based nanocomposites filled with silica (SiO 2 ) nanoparticles were prepared and the relationships between their structure and properties were investigated. Silica nanoparticles were synthesized by Stober method. Surface of silica nanoparticles were successively functionalized in order to promote matrix/filler compatibilization and to improve interfacial adhesion. Morphological analysis performed on the fractured surface of samples revealed that the compatibilization process permitted to obtain an homogeneous and discrete distribution of the nanoparticles into polymeric matrix. Mechanical test showed that in the presence of a strong interphase, the elastic modulus increases of about 25% than the neat polymeric matrix value. Preliminary modelling analysis was also performed in order to assess the correlation existing between a computational model and experimental data.