Luis C. Mendes

Degradation of polymeric restorative materials subjected to a high caries challenge.

OBJECTIVES The aim of this study was to evaluate the degradation of different resin filling materials after a caries challenge, by high performance liquid chromatography (HPLC) and contact angle (θ) measurement. METHODS Four different polymeric restorative materials (a resin composite, a polyacid-modified resin composite, an ormocer and a resin-modified glass ionomer cement) were tested. Five samples (30 mm × 6 mm × 2 mm) of each material were formed in a Teflon mold, following the manufacturers instructions. After pH cycles, the solutions were injected in an HPLC. The θ was obtained, before and after pH cycle, by a goniometer at 60% air humidity and 25°C. A distilled water drop (0.006 ml) was put on the material surface, and after 6 min, 10 measures were obtained at 20s intervals. Each sample received 4 drops, one at a time, on different areas. RESULTS HPLC results showed elution of byproducts in all materials. This was greater in the acid medium. Bis-GMA and TEGDMA were detected in TPH Spectrum and Definite residues. Analyses of the contact angle by ANOVA and Student-Neuman-Keulss test showed that the surfaces of TPH Spectrum, Dyract AP and Definite were altered, except Vitremer (p<0.05). SIGNIFICANCE All materials tested degraded on a caries simulated medium, suggesting that a great effort should be made to disseminate oral health information, since a high caries challenge environment (low pH) can lead to dental composite degradation, with potential toxic risks to patients.

Sulfonated polyaniline: influence of sulfonation routes on its thermal and structural characteristics

In order to study the influence of different sulfonation routes on its thermal and structural properties sulfonated polyaniline (SPAni) was prepared. FT-IR revealed that the formation of PAni salt or ring sulfonation depends on the route. UV-visible spectra pointed out that the level of the PAni protonation was dependent on the sulfonation route. A new approach was given for TG/DTG and DSC results correlating different energy levels with the distinguished sulfonation routes. The TG/DTG degradation steps and the amount of the released material corroborated the structural differences of the polyanilines. For each DSC first regime of heating, a broad and intense peak (from -30 to 250 oC) with different level of energy was noticed. That peak could be ascribed to the multiple relaxations and breaking of the PAni intra and inter hydrogen bonds after sulfonation.

Compatibility of iPP/HOCP binary blends by OM, DSC, DMTA and 13C nuclear magnetic resonance

Abstract The study of miscibility of the isotactic polypropylene (iPP)/hydrogenated oligo(cyclopentadiene) (HOCP) blends was performed by using OM, DSC, DMTA and 13C NMR techniques. The proton spin-lattice relaxation time in the rotating frame by using 13C spectra cross-polarization/magic-angle spinning (CP/MAS) of iPP, HOCP and their blends were determined. These blends showed phase separation. Two amorphous phases were observed: one rich in the high molecular weight component (iPP) and another one rich in the low molecular weight component (HOCP). This behaviour was similar to one observed for HDPE/HOCP blends. The results indicated that compression moulded samples of iPP/HOCP blends formed a partially miscible system, while in literature it was found that extruded isotropic films of this blend displayed as a miscible system. The iPP-HOCP interaction is influenced by the composition, the crystallization process, the solidification time and the specimen preparation.

Changes in Properties of PET/PC Blend by Catalyst and Time

The effects of the catalyst and residence time on poly(ethylene terephthalate)/polycarbonate blends (PET/PC) were studied. The Tg increased, while the Tm decreased with catalyst content and residence time as a consequence of exchange reactions during the processing. The extent of these reactions also influenced the crystal size of PET. Additionally, impact and tension properties were influenced by the level of transesterification reactions. The best value of impact was 89,7 ± 0,9 J · m for the PET/PC blend which contained 75 × 10−3 wt% of catalyst and 10 min of residence time, which represents a fourfold increase over the neat PET. Concerning elastic modulus, the best value was 60% higher than plain PET due to a higher amount of PC chains inserted in the PET. The melt flow index showed that the presence of PC enhanced the thermal stability of PET due to the formation of PET/PC copolymers.

Zirconium phosphate organically intercalated/exfoliated with long chain amine

Nanolayered zirconium phosphate was synthesized by the direct precipitation reaction method, and it was organically modified with long chain amine (octadecylamine) at different amine:phosphate ratios (0.5:1, 1:1, and 2:1). Both zirconium phosphate and amine were dispersed in a 2:1 ethanol/water solution. Infrared spectroscopy (FT-IR), thermogravimetry (TG/DTG), differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM) were used for characterization. The amine:phosphate ratio regulated the amine insertion in the zirconium phosphate lamellae, as observed by infrared bands, thermal curves, and SEM images. Different TG/DTG degradation temperatures evidenced adsorbed and bonded amine molecules in the phosphate lamellae. Calorimetric results indicated several amine melting temperatures suggesting different crystal arrangements in the phosphate galleries. The presence of octadecylamine changed the crystallographic features of the zirconium phosphate as observed in WAXD.

Miscibility of PET/PC Blends Induced by Cobalt Complexes

Amorphous miscible PET/PC copolymers were prepared by blending the two constituent blend homopolymers at 50/50 wt% proportion in presence of cobalt acetylacetonate II and III (0.05 and 0.1 wt%) in the molten state. The reaction products were evaluated by solubility in methylene chloride (CH2Cl2), differential scanning calorimetry (DSC), thermogravimetry (TGA), and Fourier transform infrared spectroscopy (FT-IR). Two fractions were obtained by extracting the blend with CH2Cl2: one soluble, rich in PC, and another one insoluble, rich in PET. The DSC showed a unique glass transition temperature (Tg) (around 100°C) and the absence of melting temperature peak of PET, indicating that an amorphous copolymer was obtained. The Tg value coincides with Fox and Couchmans calculations and indicates the formation of a miscible system. TGA curves of the blends showed thermal degradation between that of the homopolymers. FT-IR showed a decrease of PC carbonyl band at 1773 cm−1, a broadening of PET ester carbonyl band at 1720 cm−1, a decrease of PET degree of order and a new band at 1063 cm−1 attributed to the formation of aromatic-aromatic ester structure in the copolymer. The composition of CH2Cl2 insoluble and soluble phases were determined by FT-IR from calculation using the molar absorptivity of PC p-disubstituted ring band (558 cm−1) and Lambert-Beers law. The results indicated that exchange reactions took place, predominantly alcoholysis and acidolysis, and were to some extent dependent on the type and amount of cobalt complexes.

High density polyethylene and zirconium phosphate nanocomposites

Nanocomposite based on high density polyethylene (HDPE) and layered zirconium phosphate organically modified with octadecylamine (ZrPOct) was obtained through melt processing. The ZrPOct was synthesized by precipitation and modified by suspension and sonication procedures. The initial and maximum degradation temperatures (Tonset and Tmax) were increased. A slight decrease of crystallinity degree was detected. Reduction of elastic modulus and elongation at break were noticed. The lamellar spacing was increased (3.3 times higher). The storage modulus decreased and low field nuclear magnetic resonance (LFNMR) revealed an increasing of molecular mobility. The presence of octadecylamine enhanced the entrance of HDPE in the ZrPOct galleries. Several characteristics of HDPE were changed indicating that intercalation was successful. All results indicated that partially intercalated and/or exfoliated nanocomposite was achieved.

Organically modified concrete waste with oleic acid

The aim of this study is to modify demolition concrete waste (CW) with oleic acid (OA), to be used as filler in polymeric composites for the building industry. The OA was chosen in order to ease the mixing of the CW into the polymeric matrix. In this article, we report the preparation and characterization of this CW–OA filler. After crushing and sifting, the CW particles were chemically modified with OA via sonication. The results of the modification were assessed using X-ray fluorescence, Fourier transform infrared spectroscopy, thermogravimetry, differential scanning calorimetry, wide angle X-ray diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray detector. The FT-IR spectrum revealed that the OA was bonded to the surface of the CW particles by the carboxylate group. The TG/DTG curves showed an increase in the thermal stability of the OA, due to this bonding on the CW surface. The SEM and EDX analysis showed the insertion of OA on the CW surface. The results suggest that the proposed CW–OA modification was successful. This material can be used as an interesting eco-friendly filler in polymeric composites.

Thermal properties and phase structure of PP + oligopinene blends

Abstract Blends of polypropylene (PP) and β-oligopinene, a synthetic low molar mass resin, were prepared by melt mixing in a Haake Rheocord at 473 K, 30 rpm during 600 s. The influence of the terpenic resin on the thermal properties, phase structure and crystallization of PP was evaluated. The DSC results indicated the presence of phase separation. The SEM analysis shows that the oligopinene was extracted along the whole surface and it was observed entities as cut cylinder atributted to low molar mass PP. The isothermal crystallization of blends was conducted at 396, 398 and 403 K. The mixtures did not show phase separation in molten, during crystallization and after solidification. The spherulite radial growth rate of PP decreased and was dependent on the temperature and composition. The results indicated that the system is an immiscible blend with at least three phases: a fine dispersion of the oligopinene in the amorphous PP, some boundary solubility of PP in oligopinene and a crystalline PP.

Blend compatibility study by solid-state 13C nuclear magnetic resonance

Abstract The application of proton spin–lattice relaxation time in the rotating frame and carbon-13 cross-polarization/magic-angle spinning to investigate the compatibility of a polymeric blend formed by high-density polyethylene (HDPE) and a synthetic petroleum resin of low molecular weight showed that this system presents a range of compatibility varying up to 40% (w/w) of the petroleum resin. The blends showed a shift of the NMR lines to short contact time—i.e., a rigid region. The 60/40 blend clearly displays the presence of domains of distinct mobility: one rigid (short contact time) and the other flexible (long contact time), indicating phase separation. Thus, besides the crystalline phase of HDPE, the blends show two amorphous phases: one rich in the polyolefin and the other rich in the low-molecular-weight component.