Polyurethanes

Polyurethane (PU) and its nanocomposites based gas barrier films and coatings have established a distinctive position among various technologically important materials due to their large-scale potential applications. This review aims at highlighting the gas barrier property of polyurethane nanocomposite (PUNC) based films, membranes and coatings containing platelet-shaped fillers such as clays and graphene in PU matrix. The other fillers such as CNT, POSS, metal nanoparticles and nanocellulose have also been reviewed for their contribution in improving gas barrier property of polymers. The probable transport-mechanism of small gas molecules through PU and PUNCs have been discussed. There is also a discussion on basic PU-chemistry and effect of structure and morphology of PU on its gas barrier property. Various factors which influence the gas permeability through PU and PUNC films and coatings have been scrutinized. Some aspects of improving the gas barrier property of PUNCs have also been discussed. An emphasis is given on various proposed models for prediction of gas permeability through polymer nanocomposites. It also reviews the existing literature related to modeling and prediction of gas permeability of different PUNC membranes, films and coatings. Finally, special attention has been paid to the potential industrial applications of PUNC based films and coatings.

Polyurethane containing macroheterocyclic fragments in the main chain as fungicide materials and polymeric sorbing agents and process for the preparation thereof

Saveliev Yurii Vasyliovych, Hrekov Anatolii Petrovych, Veselov Vitalii Yakovych, Akhranovych Olena Rudolfivna

Формула / Реферат

1. Полиуретаны, содержащие макрогетероциклические фрагменты в основной цепи полиме­ра, общей формулы

R4- [-OCHN-R1-CONH-R2-NHCOO-R3-OCONH-R2--NHCO-]y-R4          (І)

m = 1,2; 1-0,1.

в качестве фунгицидных материалов и полимер­ных сорбентов.

2. Способ получения полиуретанов формулы 1, отличающийся тем, что форполимер с концевыми изоцианатными группами подвергают взаимодей­ствию в растворе диметилформамида с удлините­лем макроцепи, при этом в качестве удлинителя макроцепи используют дигидразиды карбоновых кислот и дигидразиды дисульфонилдибензо-18(24)-краун-6(8) формулы (II).

m -1,2.

3. Способ по п. 2, отличающийся тем, что дигидра­зиды карбоновых кислот и дигидразиды дисульфо-нилдибензо -18(24) -краун- 6(8) берут в соотноше­нии (0,05-1,0): 1,0.

4. Способ по п. 2, отличающийся тем, что дигидра­зиды карбоновых кислот,и дигидразиды дисульфонилдибензо -18 (24) – краун -6 (8) берут в соотношении (0,4-1,1):1,0, с блокированием концевых изоцианатных групп гидразидами моносульфониддиоензо-15(18) краун-5(6) формулы (III).

1 - 0,1.

5. Способ по п. 1, отличающийся тем, что взаимо­действие форполимера с удлинителем цепи прово­дят при температуре от комнатной до 60°С с последующей выдержкой при 60°С в течение 2 ча­сов по окончании синтеза полимеров.

This study investigated the fracture resistance of maxillary acrylic resin complete dentures subjected to long-term water immersion. Maxillary acrylic resin complete dentures were fabricated from five denture base resins. Half of the dentures were stored in water for 50 h, and the other half were kept in water for 180 days before testing. Ten specimens were fabricated per group. The flexural load at the proportional limit (FL-PL) of the dentures was tested. A two-way anova revealed a significant difference in FL-PL because of the denture base material variable. There were no significant differences in FL-PL because of the effect of water immersion and the interaction between the effect of water immersion and the denture base material. The FL-PLs of the dentures fabricated with the two conventional heat-processed resins, the pour-type autopolymerizing resin and the microwave energy-processed resin were not significantly different from each other; they were significantly higher than the light-activated resin in regard to their FL-PL. The FL-PLs of the maxillary acrylic resin complete dentures did not change after long-tern water immersion, and the FL-PL of the denture fabricated from the light-activated resin was lower than those of the other materials.

In this paper, a new type of rigid polyurethane, called "wood imitation polymer" with the highest free rise density (FRD) of 700 grams per liter, was prepared without filler materials. The purpose of this study was to synthesis wood foam to generate an industrial product. In this regard, primary polyols, catalyst, and surfactant were mixed with appropriate formulation; the viscosity and the hydroxyl number of the final mixture were analyzed. Finally, formulated polyol was mixed with polymerized methylene diphenyl diisocyanate (pMDI) under appropriate circumstances, and the results of reaction times, free rise density, and scanning electron microscopy (SEM) of wood foam were investigated. (a) Formulated polyol with isocyanate (b) Final wood foams with several FRD (c) SEM image of polyurethane wood foam References:

To evaluate the radiopacity, ultimate tensile strength (UTS), microhardness (KHN), degree of conversion (DC), water sorption (WS) and solubility (SL) of experimental adhesives. Five experimental adhesives with different concentrations of barium-borosilicate oxide microfillers [0% (R0), 30% (R30), 40% (R40), 50% (R50), 60% (R60)] were formulated based on the adhesive system Ambar (FGM). The adhesive Adper Single Bond 2 (SB, 3M ESPE) was used as commercial reference. For the radiopacity (n = 5), KHN (n = 5), WS (n = 10), and SL (n = 10) tests, adhesive disks were constructed (5.0 mm in diameter and 1.0 mm thick), while for UTS (n = 5), hourglass-shaped specimens with a cross-sectional area of 0.8 mm2 were used. The FTIR spectra of unpolymerized and polymerized adhesives were used to determine the DC. Data were submitted to a one-way ANOVA and Tukey's test (α = 0.05). All experimental adhesives showed radiopacity similar to enamel, except those of R0 and SB. Filler addition did not...

Two commercially available dentine-adhesive systems, Tenure and Tripton, were tested in two different cavity designs by placing 132 Class V composite restorations in cervical lesions of 35 patients. In Group A, the cervical restorations were placed totally in dentine without any intentional enamel involvement. In Group B, they were placed in dentine with adjacent enamel margins bevelled and acid etched. The retention rate, the evidence of clinical microleakage, and the marginal integrity were monitored over a 2-year period. The results of this clinical investigation indicate a high failure rate when only dentinal bonding was involved. A loss rate of 30% for Tenure and 55% for Tripton was noted in Group A after 2 years of clinical service. However, both adhesive systems used in combination with micromechanical retention on the enamel border (Group B) performed extremely well with only one restoration each having debonded over the 2-year period. Identically, marginal integrity and evidence of clinical microleakage more severely deteriorated with time for the Group A restorations in comparison with their Group B counterparts. In summary, the overall results were more positive for Tenure than for Tripton. It is concluded that micromechanical retention by acid etching of the enamel margin is still indispensable for the clinical success of cervical Class V composite restorations, primarily for retention and clinical microleakage and also, but to a lesser degree, for marginal adaptation.

The aim of this study was to evaluate two-body wear of five indirect composites and compare them with enamel. Signum, belleGlass HP, SR Adoro, Dialog, GC Gradia and enamel were formed into cylinders (n = 10). Two-body abrasive wear rates were determined using a porcelain disk and a pin on disk apparatus. The height and weight loss of the specimens were measured by stereomicroscope and digital scale. The data were subjected to analysis of variance and Tukey HSD tests to determine significant differences (alpha = 0.05). GC Gradia showed significantly less wear resistance than the other materials. Enamel was more resistant than any of the tested composites. Within the limitations of this study it can be concluded that the type of resin, filler size and method of polymerization could have affect the two-body abrasion resistance of indirect composites.

In order to select a candidate segmented polyurethane (SPU) elastomer for cardiovascular prostheses, a series of physical tests was carried out on five commercially available biomedical polyurethanes. The tests were performed on uniformly thick sheets (0.2-0.3 mm), obtained by solvent casting from THF (Cardiothane 51, Pellethane 2363 80A, Estane 5714 F1, and Estane 58810) or DMAC (Biomer). Tensile mechanical tests at 23 and 37 degrees C showed for all the copolymers typical stress/strain behaviour of elastomeric materials, with small individual differences. Hydrolytic stability was investigated at 85, 60, and 37 degrees C, at increasing times of exposure (96-168 h), in water or alkaline buffer (pH = 10). As indicated by gel permeation chromatography, in almost all cases a degradation of the molecular weight (particularly the M w) was noticed after the hydrolytic tests, but tensile, thermal (by DSC) and dynamic mechanical properties were substantially not affected. SEM was also perfo...

The aim of this study was to evaluate the effectiveness and retention of occlusal sealing using FluroShield or Compoglass. The sample consisted of 57 children aged 7 to 9 years who had 4 sound, fully erupted, first permanent molars (total=228 teeth). Both materials were applied on contralateral teeth in a split-mouth design in 2 groups: (1) FluroShield--left upper molar and right lower molar; (2) Compoglass--right upper molar and left lower molar. The materials were applied under cotton roll isolation by the same operator according to the manufacturers' instructions. The evaluations were carried out at 6, 12, and 24 months. The data were subjected to the G2 (likelihood ratio chi-square test; P<.05). At the 6-month evaluation, Compoglass showed 60% total retention, 23% partial retention, and 17% total loss. FluroShield showed 53% total retention, 31% partial retention, and 16% total loss. At the 12-month recall, Compoglass and FluroShield, respectively, showed 39% and 43% tota...

The aim of this study is to determine the differences in primary stability between conical and cylindrical dental implants. The insertion and removal torques were the parameters used to measure the primary stability of the implants. Ten conical and cylindrical dental implants were positioned in polyurethane foam blocks to simulate bone density classes D1, D2, D3 and D4. The insertion and removal torques were quantified using a digital torque gauge. The maximum insertion torque and the maximum removal torque measured for the D1 and D4 synthetic bone were significantly higher for the conical implants than the cylindrical implants. In this in-vitro model, conical implants show significantly higher primary stability than cylindrical implants for the D1 and D4 synthetic bone classes.

Acticoat, a new silver-coated dressing, produces a moist healing environment along with the sustained release of ionic silver for improved microbial control. These properties suggest that Acticoat might be a useful donor site dressing. However, there are no human studies which assess Acticoat for this use. The purpose of this study was to compare the healing of human skin graft donor sites dressed with Acticoat, to the healing of those dressed with Allevyn, an occlusive moist-healing environment material, which is our standard donor site dressing. In burn patients who had undergone burn excision and grafting, identical side-by-side split thickness donor site wound pairs were dressed with Allevyn and Acticoat. Re-epithelialization was directly assessed daily by a single observer from post-operative day 6 onward, and by four independent observers who rated the extent of re-epithelialization by viewing standardized digital images of the wounds that had been obtained on post-operative days 6, 8, 10,and 12. Donor sites were swabbed for bacterial culture on days 3, 6, and 9. Subsequently, each study donor site scar was rated by a blinded observer using the Vancouver Scar Scale at 1, 2, and 3 months. Sixteen paired sites in 15 patients (3 female, 12 male) were studied. Donor sites dressed with Allevyn were >90% re-epithelialized at a mean of 9.1±1.6 days while donor sites dressed with Acticoat required a mean of 14.5±6.7 days to achieve >90% re-epithelialization (P=0.004). The Allevyn sites had significantly greater estimated re-epithelialization at days 6, 8, 10 and 12 than the Acticoat sites based on the observations of the digital images. There were no significant differences in the incidence of positive bacterial cultures with either dressing at days 3, 6, and 9. Donor sites dressed with Acticoat had significantly worse scars at 1 and 2 months but this difference resolved by 3 months. Our findings do not support the use of Acticoat as a skin graft donor site dressing.