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Achim Stolle - One of the best experts on this subject based on the ideXlab platform.
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influence of reaction parameters on the depolymerization of h2so4 impregnated cellulose in planetary ball mills
Powder Technology, 2016Co-Authors: Robert Schmidt, Sindy Fuhrmann, Lothar Wondraczek, Achim StolleAbstract:Abstract The depolymerization of acid-impregnated cellulose in planetary ball mills was investigated under the perspective of the influence of reaction parameters. Several process, technological and chemical parameters were examined. It was found that with a higher rotation frequency νrot, smaller milling balls and a milling ball filling degree ΦMB of approximately 0.3, the highest solubility could be reached and the milling time could be reduced. The use of milling vessels with larger diameter was beneficial. Variation of the milling ball material showed huge influence and a linear correlation between solubility and density of the milling ball material was observed. Kinetic investigations indicate that the degradation of the impregnated cellulose follows a first order model.
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Influence of reaction parameters on the depolymerization of H 2 SO 4 -impregnated cellulose in planetary ball mills
Powder Technology, 2016Co-Authors: Robert Schmidt, Sindy Fuhrmann, Lothar Wondraczek, Achim StolleAbstract:Abstract The depolymerization of acid-impregnated cellulose in planetary ball mills was investigated under the perspective of the influence of reaction parameters. Several process, technological and chemical parameters were examined. It was found that with a higher rotation frequency νrot, smaller milling balls and a milling ball filling degree ΦMB of approximately 0.3, the highest solubility could be reached and the milling time could be reduced. The use of milling vessels with larger diameter was beneficial. Variation of the milling ball material showed huge influence and a linear correlation between solubility and density of the milling ball material was observed. Kinetic investigations indicate that the degradation of the impregnated cellulose follows a first order model.
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effect of reaction parameters on the synthesis of 5 arylidene barbituric acid derivatives in ball mills
Organic Process Research & Development, 2015Co-Authors: Robert Schmidt, Christine Friederike Burmeister, Matej Balaž, Arno Kwade, Achim StolleAbstract:The influence of crucial reaction parameters on Knoevenagel condensation in planetary ball mills was investigated. Rotation frequency (νrot), milling ball diameter (dMB), milling ball filling degree (ΦMB), and beaker size had obvious influences on yield. It was found that higher νrot, lower dMB, milling beakers with larger diameter, and a ΦMB of ∼0.3 are advantageous for the reaction. Furthermore, the influence of the type of mill was investigated, including reactions performed in different planetary and mixer ball mills, in a stirred media mill, and with a mortar mill. Comparisons with the other solvent-free synthetic routes showed that ball milling is an effective way of performing the reaction with low energy intensity.
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scale up of organic reactions in ball mills process intensification with regard to energy efficiency and economy of scale
Faraday Discussions, 2014Co-Authors: Achim Stolle, Robert Schmidt, Katharina JacobAbstract:The scale-up of the Knoevenagel-condensation between vanillin and barbituric acid carried out in planetary ball mills is investigated from an engineering perspective. Generally, the reaction proceeded in the solid state without intermediate melting and afforded selectively only one product. The reaction has been used as a model to analyze the influence and relationship of different parameters related to operation in planetary ball mills. From the viewpoint of technological parameters the milling ball diameter, dMB, the filling degree with respect to the milling balls' packing, ΦMB,packing, and the filling degree of the substrates with respect to the void volume of the milling balls' packing, ΦGS, have been investigated at different reaction scales. It was found that milling balls with small dMB lead to higher yields within shorter reaction time, treaction, or lower rotation frequency, rpm. Thus, the lower limit is set considering the technology which is available for the separation of the milling balls from the product after the reaction. Regarding ΦMB,packing, results indicate that the optimal value is roughly 50% of the total milling beakers' volume, VB,total, independent of the reaction scale or reaction conditions. Thus, 30% of VB,total are taken by the milling balls. Increase of the initial batch sizes changes ΦGS significantly. However, within the investigated parameter range no negative influence on the yield was observed. Up to 50% of VB,total can be taken over by the substrates in addition to 30% for the total milling ball volume. Scale-up factors of 15 and 11 were realized considering the amount of substrates and the reactor volume, respectively. Beside technological parameters, variables which influence the process itself, treaction and rpm, were investigated also. Variation of those allowed to fine-tune the reaction conditions in order to maximize the yield and minimize the energy intensity.
Robert Schmidt - One of the best experts on this subject based on the ideXlab platform.
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influence of reaction parameters on the depolymerization of h2so4 impregnated cellulose in planetary ball mills
Powder Technology, 2016Co-Authors: Robert Schmidt, Sindy Fuhrmann, Lothar Wondraczek, Achim StolleAbstract:Abstract The depolymerization of acid-impregnated cellulose in planetary ball mills was investigated under the perspective of the influence of reaction parameters. Several process, technological and chemical parameters were examined. It was found that with a higher rotation frequency νrot, smaller milling balls and a milling ball filling degree ΦMB of approximately 0.3, the highest solubility could be reached and the milling time could be reduced. The use of milling vessels with larger diameter was beneficial. Variation of the milling ball material showed huge influence and a linear correlation between solubility and density of the milling ball material was observed. Kinetic investigations indicate that the degradation of the impregnated cellulose follows a first order model.
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Influence of reaction parameters on the depolymerization of H 2 SO 4 -impregnated cellulose in planetary ball mills
Powder Technology, 2016Co-Authors: Robert Schmidt, Sindy Fuhrmann, Lothar Wondraczek, Achim StolleAbstract:Abstract The depolymerization of acid-impregnated cellulose in planetary ball mills was investigated under the perspective of the influence of reaction parameters. Several process, technological and chemical parameters were examined. It was found that with a higher rotation frequency νrot, smaller milling balls and a milling ball filling degree ΦMB of approximately 0.3, the highest solubility could be reached and the milling time could be reduced. The use of milling vessels with larger diameter was beneficial. Variation of the milling ball material showed huge influence and a linear correlation between solubility and density of the milling ball material was observed. Kinetic investigations indicate that the degradation of the impregnated cellulose follows a first order model.
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effect of reaction parameters on the synthesis of 5 arylidene barbituric acid derivatives in ball mills
Organic Process Research & Development, 2015Co-Authors: Robert Schmidt, Christine Friederike Burmeister, Matej Balaž, Arno Kwade, Achim StolleAbstract:The influence of crucial reaction parameters on Knoevenagel condensation in planetary ball mills was investigated. Rotation frequency (νrot), milling ball diameter (dMB), milling ball filling degree (ΦMB), and beaker size had obvious influences on yield. It was found that higher νrot, lower dMB, milling beakers with larger diameter, and a ΦMB of ∼0.3 are advantageous for the reaction. Furthermore, the influence of the type of mill was investigated, including reactions performed in different planetary and mixer ball mills, in a stirred media mill, and with a mortar mill. Comparisons with the other solvent-free synthetic routes showed that ball milling is an effective way of performing the reaction with low energy intensity.
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scale up of organic reactions in ball mills process intensification with regard to energy efficiency and economy of scale
Faraday Discussions, 2014Co-Authors: Achim Stolle, Robert Schmidt, Katharina JacobAbstract:The scale-up of the Knoevenagel-condensation between vanillin and barbituric acid carried out in planetary ball mills is investigated from an engineering perspective. Generally, the reaction proceeded in the solid state without intermediate melting and afforded selectively only one product. The reaction has been used as a model to analyze the influence and relationship of different parameters related to operation in planetary ball mills. From the viewpoint of technological parameters the milling ball diameter, dMB, the filling degree with respect to the milling balls' packing, ΦMB,packing, and the filling degree of the substrates with respect to the void volume of the milling balls' packing, ΦGS, have been investigated at different reaction scales. It was found that milling balls with small dMB lead to higher yields within shorter reaction time, treaction, or lower rotation frequency, rpm. Thus, the lower limit is set considering the technology which is available for the separation of the milling balls from the product after the reaction. Regarding ΦMB,packing, results indicate that the optimal value is roughly 50% of the total milling beakers' volume, VB,total, independent of the reaction scale or reaction conditions. Thus, 30% of VB,total are taken by the milling balls. Increase of the initial batch sizes changes ΦGS significantly. However, within the investigated parameter range no negative influence on the yield was observed. Up to 50% of VB,total can be taken over by the substrates in addition to 30% for the total milling ball volume. Scale-up factors of 15 and 11 were realized considering the amount of substrates and the reactor volume, respectively. Beside technological parameters, variables which influence the process itself, treaction and rpm, were investigated also. Variation of those allowed to fine-tune the reaction conditions in order to maximize the yield and minimize the energy intensity.
Zvi Metzger - One of the best experts on this subject based on the ideXlab platform.
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the unpredictability of seal after post space preparation a fluid transport study
Journal of Endodontics, 2001Co-Authors: Itzhak Abramovitz, Ronit Lev, Zvi Fuss, Zvi MetzgerAbstract:A root canal filling remaining after post space preparation is commonly expected to provide adequate seal. Coronal leakage of 30 endodontically treated teeth was measured before post space preparation using a fluid transport assay. In 10 of these teeth post space was prepared, using a two-step procedure, first to a remaining filling of 6 mm and then to 3 mm, with the leakage studied after each step. In 10 teeth the removal was done in one step to a remaining length of 3 mm. The other 10 teeth, with intact root canal fillings, served as controls and were tested twice for leakage. A significant difference was found between the sealing ability of intact fillings and that of partially removed ones (p
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correlation between remaining length of root canal fillings after immediate post space preparation and coronal leakage
Journal of Endodontics, 2000Co-Authors: Zvi Metzger, Itzhak Abramovitz, Revital Abramovitz, Michael TaggerAbstract:The seal provided by root canal fillings after post space preparation was studied using a pressure-driven radioactive tracer assay. The coronal part of root canal fillings was immediately removed, using a hot plugger, to a remaining length of either 3, 5, 7, or 9 mm. Intact root canal fillings of 14 mm served as control. Application of air pressure of 130 mm Hg to the tracer solution drove it through the fillings and into phosphate-buffered saline surrounding the apex. Leakage gradually increased for 28 days, and differences in the leakage through 3 to 9 mm fillings were demonstrated. In a passive system by which an additional group of teeth were tested none of these differences could be detected. It was concluded that: (a) root canal fillings of 3, 5, and 7 mm have an inferior seal, compared with that of an intact filling; (b) the sealing is proportional to the length of the remaining filling; and (c) a passive system is unable to detect these differences, even when conducted for as long as 28 days.
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the effect of immediate vs delayed post space preparation on the apical seal of a root canal filling a study in an increased sensitivity pressure driven system
Journal of Endodontics, 2000Co-Authors: Itzhak Abramovitz, Michael Tagger, Aviad Tamse, Zvi MetzgerAbstract:A 5 mm remaining length of root canal filling, after post space preparation, is commonly assumed to maintain sealing ability similar to that of the intact filling. Post spaces were prepared either immediately using hot pluggers, or later, using drills. The sealing ability of the fillings, 5 mm remaining length, were compared with each other and with an intact root canal filling control, using radioactive tracer in a pressure-driven system. When no pressure was applied, no differences could be detected between either of the groups and the control. When a pressure of 120 mm Hg was applied to the same teeth, the control group clearly maintained a better seal than each of the experimental groups, which did not significantly differ from each other. These results suggest that (a) the pressure-driven system was more sensitive than the passive leakage assay that failed to detect differences even at 14 days; (b) a remaining root canal filling of 5 mm was inferior to the intact root canal filling; and (c) the immediate post space preparation with hot pluggers did not differ from a delayed preparation with drills.
P R Wesselink - One of the best experts on this subject based on the ideXlab platform.
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leakage along apical root fillings with and without smear layer using two different leakage models a two month longitudinal ex vivo study
International Endodontic Journal, 2006Co-Authors: Hagay Shemesh, P R WesselinkAbstract:Aim To compare two different experimental models when measuring leakage along root fillings with or without smear layer. Methodology One hundred and twenty singlerooted teeth were prepared to size 50 and allocated to two groups: fluid transport model (n ¼ 60) and glucose penetration model (n ¼ 60). The roots in each group were divided into three subgroups of 20 teeth each. Smear layer was left in place in group 1 but removed in groups 2 and 3. In groups 1 and 2 canals were filled with laterally compacted gutta-percha cones and AH 26. Group 3 was laterally compacted with Resilon cones and Epiphany sealer. The coronal portion of the filling was removed to assure only 4 mm of filling remained in the canal. Leakage of glucose was evaluated by measuring its concentration once a week for a total period of 56 days using a glucose penetration model. Fluid transport was evaluated by measuring the movement of an air-bubble using a fluid transport model, 1 and 8 weeks after canal filling. Differences between the groups in glucose concentrations and fluid transport were statistically analysed with the Kruskal‐ Wallis and the Mann‐Whitney tests. The level of significance was set at a ¼ 0.05. Results Glucose penetration was significantly different between the three groups after the first 8 days (P 0.05) existed between the two gutta-percha groups at all time intervals (Mann‐Whitney test). In the fluid transportation model, no statistically significant differences were observed between all three experimental groups (P > 0.05) at either 1 or 8 weeks after filling (Kruskal‐ Wallis test). Conclusions Under the conditions of this study, the glucose penetration model was more sensitive in detecting leakage along root fillings. Removing the smear layer before filling did not improve the sealing of the apical 4 mm of filling. Resilon allowed more glucose penetration but the same amount of fluid transport as the gutta-percha root fillings.
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fluid movement along the coronal two thirds of root fillings placed by three different gutta percha techniques
International Endodontic Journal, 2003Co-Authors: L W M Van Der Sluis, C N Ardila, P R WesselinkAbstract:Aim To compare fluid movement (FM) along the coronal two-thirds of gutta percha/sealer root fillings placed by three different techniques. Methodology Three groups consisting of the roots of mandibular incisors were instrumented and obturated by cold lateral compaction (LC), warm vertical compaction (VC) or the single-cone technique (SC), using RockoSeal Automix (RSA) as the sealer. The apical 4 mm of each root filling was removed, and FM along the remaining 7 mm of the root filling was measured. Results The VC group displayed more FM than the other two groups (P=0.023). No significant difference in FM was found between the LC and SC groups (P=0.629). Conclusions The coronal two-thirds of the VC root fillings did not prevent FM when RSA sealer was used.
Michael Hulsmann - One of the best experts on this subject based on the ideXlab platform.
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comparison of hand and rotary instrumentation for removing gutta percha from previously treated curved root canals a microcomputed tomography study
International Endodontic Journal, 2014Co-Authors: Tina Rodig, J Kupis, Frank Konietschke, Christian Dullin, Steffi Drebenstedt, Michael HulsmannAbstract:Aim To compare the efficacy of hand and rotary nickel–titanium (NiTi) instruments in removing filling material from curved root canals of root filled teeth with unknown preparation parameters. Methodology Ninety mandibular molars with root fillings in curved root canals and homogenous root canal filling extending to 0-2 mm short of the radiographic apex were selected. Root canal curvatures and radii were measured in two directions and microcomputed tomography (micro-CT) scans were used to determine preoperative volumes of the filling material. Subsequently, the teeth were assigned to two identical groups (n = 14). The root fillings were removed with Hedstrom files or FlexMaster NiTi rotary instruments. Postoperative micro-CT imaging was used to assess the percentage of residual filling material as well as the amount of dentine removal. Working time and procedural errors were recorded. Data were compared using analysis of covariance and analysis of variance procedures. Results Root canals retreated with Hedstrom files were associated with less remaining filling material compared with FlexMaster instruments (P 0.05). FlexMaster instruments were significantly faster than Hedstrom files (P < 0.05). No procedural errors were detected in the Hedstrom group, whilst three instruments fractured in the FlexMaster group. Conclusions Hand instrumentation resulted in significantly less residual filling material than retreatment with rotary NiTi instruments. Dentine removal was not significantly different for both techniques. FlexMaster NiTi rotary files were significantly faster than Hedstrom files, but were associated with a higher risk of instrument fracture.