Unfilled Films Research Articles

UV-curable hyperbranched nanocomposite coatings

Nanoparticles have been used to reinforce polymer matrices since the late 1980s, with promising results. Hyperbranched polymers are densely branched molecules with a globular structure, leading to lower viscosity and many end-groups, creating property-designing opportunities. Here, the two research areas, nanocomposites and hyperbranched polymers, were combined to investigate the possibility of creating a nanocomposite resin, in order to prepare a UV-curable coating system. Nanocomposites were prepared from the hyperbranched polyester Boltorn ® H30, acrylated to 30% and 70%, and the unmodified layered silicate Na +montmorillonite, added both before and after the acrylation of Boltorn ® H30. Films prepared from 30% acrylated Boltorn ® H30 with clay added after the acrylation, having a mainly exfoliated structure according to X-ray and TEM, exhibited the largest property improvement, compared with the unfilled film. These property improvements comprised a harder surface, better scratch resistance, better adhesion to metal substrates and a small improvement in flexibility.

Degradation of Poly (DL-lactic acid-co-glycolic acid) Containing Calcium Carbonate and Hydroxyapatite Fillers-Effect of Size and Shape of the Fillers-

The effects of size and shape of calcium carbonate (CC) and hydroxyapatite (HA) fillers on the degradation of poly(DL-lactic acid-co-glycolic acid) (PLGA) were examined in the PLGA composite films containing 50 mass% of the fillers. The composite and unfilled films were prepared by our method reported previously. The films were immersed in phosphate-buffered saline (pH 7.4) at 37 degrees C for up to 12 weeks. The fate of the films was monitored by weighing and size exclusion chromatography. Blending HA and CC fillers to PLGA retarded the degradation of the PLGA matrix by obstructing the autocatalytic effect caused by carboxylic acid end groups. CC was a little more effective in retarding the degradation than HA. The size of the fillers showed a significant effect on the degradation. The effect of size was more marked in HA than in CC filler. The shape of CC filler had little effect on the degradation in the two shapes studied.

Effect of blending calcium compounds on hydrolytic degradation of poly( dl-lactic acid-co-glycolic acid)

To clarify the effect of blending calcium compounds with different acidity or basicity on the degradation of poly( dl-lactic acid-co-glycolic acid) (PLGA), composite materials composed of PLGA incorporated with 30 mass% of calcium dihydrogenphosphate (CDHP), calcium hydrogenphosphate, calcium phosphate, and calcium carbonate (CC) were prepared by mixing in dioxane followed by freeze-drying. The porous composite materials were then compressed to yield nonporous films with 0.5 mm thickness. The blend films and the unfilled films as a control were immersed in phosphate-buffered saline (pH 7.4) at 37°C. Specimens were removed at 1, 2, 3, 4, 6, and 8 weeks and subjected to measuring of water absorption, mass loss, thickness change, and molecular weight. The temporal changes in appearance and measurements for the five materials differed from each other; especially, the CC blend differed from the other four materials. The degradation of PLGA decreased with increasing basicity of the calcium compounds blended. The most basic CC was most effective to delay the degradation, while the most acidic CDHP was least effective. However, even CDHP had appreciable degradation-delaying effects compared with unfilled PLGA. Thus, the findings of the present study suggest that degradation of PLGA can be varied by blending inorganic compounds with different basicity.

The influence of basic filler materials on the degradation of amorphous D- and L-lactide copolymer

Composite films made of poly L/D copolymer and hydroxylapatite (HA) as filler material were made in two different volume percentages. As references pure copolymer films and composite films with magnesium oxide (MgO) were prepared to serve as strongly basic model filler material. All these materials were immersed in phosphate buffered saline to study the effect of filler materials on the degradation rate of the copolymer. Filled films showed less molecular weight decrease than the unfilled films, while lactate release was higher for the filled films than for the unfilled films. This effect implies that the filler materials influence the degradation mechanism by preventing the occurrence of the autocatalytic effect of the acidic endgroups, resulting from hydrolysis of the polymer chains. The polymer chains at the surface of the material are less protected by the filler materials, which causes a more rapid degradation of these chains and a higher lactate release. At the same time composites seem to show an erosion type of degradation rather than bulk degradation in unfilled materials.

The formation of network structures in polyepoxides with various filler contents (γ-iron oxide)

The effect of the polymer-filler contact area S on the parameters of the network structure of a polymeric matrix and the thermomechanical and strength properties of films has been studied. The films were prepared using an epoxide oligomer ( M n = 3200 ), cured at 200°C with a phenolformaldehyde oligomer and hexamethoxymethylmelamine, from a solvent whose solubility parameter was practically the same as that of the epoxide oligomer. The filler (γ-iron oxide) with a specific surface area, S N2, of 17 m 2/g was introduced into the composition at a rate of from 4 to 6 wt% (a value of S from 0.68 to 10.2 m 2/g). The degree of network formation in the films, determined from CHCl 3 absorption isotherms, and their strength remains practically unchanged for values of S up to 3.4 m 2/g, as compared with the unfilled film. An increase in the density of the network of the polymeric matrix is observed with an increase in S, together with a reduction in the rupture strength of the films. The critical value for the system investigated is 60% filling ( S = 10.2 m 2/g), which leads to an increase in the density of the network by a factor of more than 2, as compared with the initial film; relaxation processes do not go the completion and there is a practically complete loss of strength.

Electrochemical and Electrochromic Properties of Polymer Complex Films Composed of Polytetramethyleneviologen and Poly-[p-Styrenesulfonic Acid] Containing a Conductive Powder

Abstract The electrochemical and electrochromic properties of polymer films containing a conductive powder (SnO2/TiO2) have been investigated. The films are complexes of polytetramethyleneviologen and poly(p-styrenesulfonic acid). It was found that the coloration (purple) and bleaching rates of the composite films increase markedly with increasing conductive powder content(x). The coloring and bleaching of the composite film with x = 95 wt% were about 7 and 44 times faster, respectively, than those for an equivalent film without conductive powder. This increase in the rate of color change by introduction of a conductive powder was found to be correlated with the apparent diffusion coefficient (D app) for the diffusionlike charge-transport process within the composite films which increases with increasing x. The D app for the reduction process of the film with x = 95 wt% was larger by about 3 orders of magnitude than that for the unfilled film.

Sorption of water by polyester melamine films of network structure

A study has been made of the sorption of water by filled and unfilled polyester melamine films based on carboxyl- and hydroxyl-containing polyesters differing as to the length of side chains. Sorption of water by the unfilled films is nonlocalized in character, while the introduction of titanium dioxide leads to intensification of H 2O interaction with the films at low relative pressures. The network density affects the kinetics of the sorption process. Depending on the mobility of the chains and on the existence of internal stress structural transformations occur during the sorption of water and involve repacking of macrochains of polyester melamine films. These transformations are relaxation type structural regrouping processes.

Diffusion and Permeation of Gases in Fiber-Reinforced Composites

Abstract The presence of filler in a matrix phase greatly alters and also complicates the diffusion process, making experimental data very difficult to handle analytically. In this study both diffusion and permeability data were obtained in unfilled cellulose acetate films and cellulose acetate films filled with cheese cloth. Cheese cloth being highly permeable, the permeabilities and diffusivities of gases in the filled films are greater than in unfilled films due to reduced effective film thickness for molecular diffusion. A mathematical model has been developed which considers molecular diffusion to occur in that part of the film having no filler, while diffusion through the low-resistance cheese cloth is approximated by convective flow controlled only by the pressure gradient across the thickness of the cheese cloth yarn. The mathematical model predicts permeability values somewhat lower than experiment at low flow rates, but agrees well with experimental permeabilities at higher rates. The poor agree...