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Introduction Pure gutta-percha (trans-1, 4-polyisoprene [TPI]) has been used extensively as a main component of gutta-percha for root canal filling. TPI has the interesting shape memory property by cross-linking, and this polymer was commercialized under the product name of SMP-2 (Kuraray Corp, Kashima, Japan). Therefore, the purpose of this study was to examine the thermal properties and the mechanism of the shape memory function of cross-linked SMP-2. Methods The crystalline of the TPI was observed by x-ray diffraction. The effects of temperature on shape recovery, recovery stress, and relaxation modulus (Er[5]) were measured in cross-linked cylindrical specimens of SMP-2. Differential scanning calorimetry was used to monitor thermal events. Results On heating, a pronounced increase in recovery stress, a marked decrease in Er(5), and endothermic DSC peaks were observed over the same temperature range (38°–51°C) with shape recovery. On the other hand, on cooling, a pronounced decrease in recovery stress, a marked increase in Er(5), and an exothermic DSC peak were observed over the same temperature range (27°–33°C). Conclusions The shape memory property of TPI is derived from its crystallinity and cross-linking ability. Fixing the deformed shape and shape recovery from the deformed shape to the original shape is relatively easy to achieve by changing the temperature of SMP-2. The shape memory function of the cross-linked SMP-2 was expected to be very useful as a root canal filling material by the modification of its some thermal properties. [ABSTRACT FROM AUTHOR]

Basal media including Murashige and Skoog (MS), Woody Plant Medium (WPM), and Driver and Kuniyuki (DKW) media were compared for use in guayule regeneration and propagation. Explants grown on MS basal medium showed large size calli with multiple shoots, but the calli produced on DKW medium were of higher quality, and longer true shoots were produced. Adventitious root formation was best in WPM basal medium. A comparison of macro and micro nutrient levels in MS, DKW, and WPM media revealed significant differences in the calcium levels. Under controlled conditions, guayule plants in vitro incorporated calcium into plant tissues in proportion to the amount available. Moreover, the addition of calcium nitrate tetrahydrate at moderate levels into MS medium significantly improved the emergence of single, elongated true shoots, suggesting a requirement for calcium in guayule tissue culture. We have further explored selection agent (antibiotic) concentration for the identification of transgenic plants using a spectinomycin resistance gene (aadA). Based on the results, we have improved tissue culture protocols for guayule including spectinomycin as the selection agent. [ABSTRACT FROM AUTHOR]

Abstract: Guayule (Parthenium argentatum Gray) is now a commercial crop for the production of high-quality, hypoallergenic natural rubber latex. Because guayule is relatively resistant to both insect and disease pests, its cultivation requires little chemical input. It has been postulated that guayule''s chemical defense system is based on terpene derivatives such as guayulins A and B. The goals of this research were to: (1) describe the distribution of guayulins A and B throughout the plant, (2) determine whether guayulins can be used as a predictor of rubber content/yield (is guayulin content related to rubber content), and (3) determine whether the guayulin content/distribution has been changed through plant breeding. Two plants each of three different lines (11591, AZ-1, and AZ-3) and two ages (1 and 2 years old) were harvested at the soil line in the fall of 2002 and spring of 2003. Plants were separated into eight parts: brown leaves, green leaves, stem tips, stems less than 5mm in diameter, stems between 5 and 10mm, stems greater than 10mm, green stems, and flower parts. Samples were analyzed for guayulins A and B and rubber content. Guayulins A and B and rubber were found in all plant parts, but were most prevalent in stems larger than 10mm in diameter, and were significantly correlated with each other in these stems. Guayulin A was found in greater concentrations than guayulin B. There were no significant differences between plant ages for rubber, or guayulin content at the time of harvest, or guayulins for harvest season. Rubber percent was higher in spring, which agrees with numerous other investigations. Guayulin A in the stems is correlated with the total rubber in the plant, suggesting it as a potential selection tool. However, rubber in the same plant parts has a higher correlation with total plant rubber and remains a better and easier selection criterion than guayulin A. The extent to which guayulin contents differed between older, relatively unimproved lines and newer improved lines was evaluated. Variety 11591 had a higher concentration of guayulin A than guayulin B, so that the ratio of A to B was much higher than in the two improved lines (AZ-1 and AZ-3). It appears that the ratio of guayulin A to guayulin B has been changed in the two newer selections, but it is unclear whether this will affect pest resistance. [Copyright &y& Elsevier]

Abstract: A comparative study on biodegradation of di-cumyl peroxide (DCP) crosslinked and uncrosslinked natural rubber by Pseudomonas sp. was carried out. Decrease in organic carbon content along with the changes in tensile strength of the treated rubber, both DCP crosslinked and uncrosslinked natural rubber, indicated rubber hydrocarbon utilization by the Pseudomonas sp. A decrease in 60.88% MPa and 41.66% MPa was observed after five month’s old treated uncrosslinked natural rubber and DCP crosslinked rubber, respectively. Biodegradation was more pronounced in natural uncrosslinked rubber, which was further confirmed by the formation of aldehydic compounds with decrease in CH2 stretching frequencies. [Copyright &y& Elsevier]

Abstract: A comparative study on natural rubber (NR) biodegradation through solid-state fermentation (SSF) and submerged fermentation (SmF) has been carried out for both bacterial as well as fungal species. Changes in the organic carbon content along with the average molecular weight of the treated rubber samples indicated rubber hydrocarbon utilization and its degradation. Proportion of sol and gel content of the treated rubber also varied with the SmF and SSF treatment. Further, presence of aldehyde groups in the treated rubber indicated rubber biodegradation. The comparative results showed SSF to be a better treatment method for rubber biodegradation. [Copyright &y& Elsevier]

Abstract: The production of latex or bulk rubber from guayule has been pursued at various times since guayule rubber ceased being an article of commerce more than 60 years ago. Hypo-allergenic guayule latex has been prepared in 25–50-kg laboratory batches. Dilute latex was first washed from ground shrub and then concentrated by a combination of multi-stage centrifugation and creaming steps. This material was used to fabricate prototype medical products. A total of 8.8t of dry guayule rubber was produced by simultaneous extraction of rubber and resin with a mixed organic solvent, followed by fractionation of the polymer stream. This material was tested in aircraft and light truck tires. At present, those seeking to process guayule must be prepared to meet several challenges: increasing the bulk viscosity of the rubber polymer, reducing the level of entrained resin and assuring oxidative and thermal stability. From this standpoint, latex process development remains in its early stages, whereas processing guayule for bulk rubber has been more thoroughly and successfully evaluated. [Copyright &y& Elsevier]