Weaker Gel Strength Research Articles

Hydrogel‐forming agar‐graft‐PVP and κ‐carrageenan‐graft‐PVP blends: Rapid synthesis and characterization

AbstractGrafting of agar and κ‐carrageenan with polyvinylpyrrolidone (PVP, average molecular weight 10,000 D) in an aqueous medium at a pH of about 7 produced agar‐graft‐PVP and κ‐carrageenan‐graft‐PVP blends capable of forming hydrogels. The reaction was carried out with microwave irradiation in the presence of a water‐soluble initiator, potassium persulfate. Optimum microwave irradiation conditions for obtaining hydrogels of the grafted products were achieved. The structural characteristics and thermal stability of the grafted blends were studied by Fourier transform infrared, 13C‐NMR, and thermogravimetric analyses. Appearance of new IR bands at 1661, 1465, and 1426 cm−1 in the grafted products indicated the insertion of PVP into the polysaccharide structure. Powder X‐ray diffraction studies revealed the enhanced crystallinity in the products compared to in the control polysaccharides as well as PVP. Agar and κ‐carrageenan were grafted to a considerable degree, with 62.5 E % and 125 G % for agar‐graft‐PVP and 65.5 E % and 131 G % for κ‐carrageenan‐graft‐PVP. Optical micrographs of the grafted blends indicated considerable changes in the morphology of the agar and the κ‐carrageenan, substantiating the X‐ray diffraction data. A plausible mechanism for the crosslinking of PVP to agar and κ‐carrageenan is proposed. These hydrogels exhibited enhanced water‐holding capacity despite weaker gel strength than that in the respective control polysaccharides. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3654–3663, 2006

Sensory Characteristics of Restructured Fresh Fruit Composite Prepared from Jack Fruit (Artocarpus heterophylla L.) and Sapodilla (MaidMara achras Mill. Fosb.)

Jack fruit and sapodilla are tropical fruits having sweet and distinctive flavor and attractive color. At present, consumers have limited choice for ready-to-eat fresh fruit products available in the market. The objective of this study was to determine the sensory characteristics of fresh fruit product composite prepared from combination ofjackfruit and sapodilla and restructured Using three different type of alginate. Three different type of alginates and two form of calcium lactate (encapsulated and non encapsulated) were used as binding ingredients. Ten panelists were employed to evaluate the freshly prepared fruit prodact composite for its taste, aroma, appearance, mouthfeel, and gel strength using a 5-point scoring. Type of alginate had no effect on the sensory properties of restructured fruit layers. However, the source of calcium in the form of encapsulated or not encapsulated powder showed significant effect on the appearence and gel strength. The fruit layers prepared using encapsulated Ca-lactate had less attractive appearence and weaker gel strength than the fruits restructured with free Ca-lactate. The two difference source of calcium had no significant effect on the products taste, aroma, and mouthfeel.

寒天印象材の石こう模型に及ぼす影響に関する研究

Taking an impression is an important clinical step in prosthetic dentistry because it links the treatment work and model technique together. Since the fabrication of the prosthesis requires indirect techniques, there are many high quality, newly developed materials available. However, hydrocolloid impression is one which has been used for quite some time. Compared with the others, the hydrocolloidimpression material has several advantages such as hydrophilia, better flow, and no requirement of pressure or mixing. But there are some disadvantages that have been pointed out: dimensional instability, weak gel strength, and impartation of a rough surface to dental stone. Many efforts have been made to alter its undesirable properties, yet still some remain. By using 4 types of hydrocolloid impression materials in two group-a) Rubberloid heavy bodied and 5/16 small stick (VAN-R) and b) Politube reqular and 3/8 stick white (SURGIDENT) and 12 types of model stones (9 dental improved hard stone and 3 hard stone), the following parameters were investigated: (1) dimensional stability, (2) accuracy, (3) effect of tray design, (4) detail reproduction, (5) surface character of stone model, and (6) the effect of fixation. According to the results obtained, the following observations can be made:(1) The hydrocolloid impression material maintained in a supersonic humidifier (100% humidity) or in a wet box (85-90% humidity) had minimal weight change while those kept in the open room environment (50% humidity) or in water were unstable. But the dimensional stability of stone casts derived from the hydrocolloid impression of the original bridge die was poor under all condition used. This suggested that a short time interval between the impression work and stone pouring as well high humidity would give good results.(2) When different stone types having different setting expansion values were used, there was no correlation between the degree of deformation and setting expansion values. Therefore dimensional changes can not be explained solely by setting expansion of the stone.(3) Comparing the retention ability of hydrocolloid impression material with different tray forms, there were the same dimensional changes with both the rimlock type tray and that without the undercut. This suggests that there is no retentive effect in the horizontal vector. The retention due to vis or perforations was similiar. Therefore separation of the impression material from the tray after the impression work probably influences dimensional change.(4) Concerning the reproduction of detail, all the hydrocolloid impression materials gave a good reproduction of a 10μm wide line, but there were differences with different dental stone. The stone crystal granule size giving good reproducibility was 5μm, and that giving the worst was 20μm. This was determined by SEM observa tion. It was suggested that the use of a granule size over 20μm would make it difficult to reproduce a 20μm wide line. Comparing the stone surfaces made from either Coltex or hydrocolloid impression material, the surface made from the hydrocolloid impression material revealed larger growing crystal granules which may be due to the surface roughness or hardness of the impression.(5) Stones whose surface character may be affected by hydrocolloid impression material were Densite, Silkyrock, Velmix, Surstone, Tewe and Rapid stones, while those not easily affected were Mode-rock, Fuji-rock, Sunrock and New metal rock as well as New plastone and Hydro-gips. Clinically, the latter group seem to have less surface roughness.