Absence Of Zinc Oxide Research Articles

64. In-feed quinine hydrochloride supplementation improved piglet growth in the absence of zinc oxide under commercial conditions

64. In-feed quinine hydrochloride supplementation improved piglet growth in the absence of zinc oxide under commercial conditions

PSIV-5 The Utilization of Alltech’s Seed, Feed, Weed Piglet Program as an Alternative to Zinc Oxide on the Growth, Feed Efficiency and Mortality of Newly Weaned Pigs

Abstract Achieving a healthy gut with a suitable microbial population in place will maximize the health and lifetime performance of piglets and, concurrently, profitability. Natural nutritional strategies that promote gut health and development in young pigs without zinc oxide (ZnO) are gaining considerable interest. Alltech’s Seed, Feed, Weed (SFW) program is designed to promote favorable microbial communities in the gut, optimize gut structures, and support the immune system; all of which will positively impact the growth and health of young piglets. The objective of this study was to investigate the effect of the SFW piglet program as an alternative to ZnO supplementation on the growth, feed efficiency and mortality of newly weaned pigs. Newly weaned pigs were allocated to one of two dietary treatments in 3 experiments. All experiments were carried out on commercial pig units in Spain. Dietary treatments were a basal pre-starter and starter diet containing 3,000 ppm ZnO (CONTROL), and a SFW piglet pre-starter and starter pack containing 0 ppm ZnO (SFW). In Exp. 1, pigs (n = 431) were weaned at 28 days old and fed the experimental pre-starter diets for 9 days. In Exp. 2, pigs (n = 295) were weaned at 28 days old and fed the experimental pre-starter and starter diets for 35 days. In Exp. 3, pigs (n = 311) were weaned at 28 days old and fed the experimental pre-starter and starter diets for 21 days. Pig performance was recorded. In experiment 1, SFW-fed pigs had similar average daily gain (ADG; 142 g/d vs 148 g/d) and average daily feed intake (ADFI; 149 g/d vs. 167 g/d) to CONTROL fed pigs. Feed efficiency (FE) was 1.05 and 1.13 for SFW and CONTROL piglets, respectively, resulting in SFW fed piglets being heavier at the end of the treatment period (7.65 kg vs. 7.45 kg). In experiment 2, overall, ADG (308 g/d vs. 316 g/d) and ADFI (423 g/d vs. 444 g/d) were similar between SFW and CONTROL fed piglets, respectively. Th SFW piglets had greater FE than CONTROL pigs (1.37 vs. 1.41). In experiment 3, there was no effect of treatment on ADG (356 g/d vs. 355 g/d) and ADFI (410 g/d vs. 420 g/d) or piglet body weight at the end of the study (12.8 kg vs. 12.7 kg). Feed efficiency was improved (1.21 vs. 1.24) and piglet mortality was reduced (3.4 % vs. 6.9 %) in SFW fed piglets compared with CONTROL fed piglets. In conclusion, the SFW program may prove to be a suitable alternative to ZnO by positively influencing the gut health of piglets and ensuring that piglet performance and health is maintained in the absence of ZnO.

Selenium-Enriched Mushroom Powder Enhances Intestinal Health and Growth Performance in the Absence of Zinc Oxide in Post-Weaned Pig Diets.

Simple SummaryThe imminent ban on zinc oxide in pig diets within the European Union is a major challenge facing the swine industry. Commercial weaning is associated with abrupt dietary, environmental and social changes resulting in stress, reduced feed intake and gut developmental issues in the post-weaned pig. Mushrooms are rich in natural bioactives and have long been regarded as a health-promoting food due to their immunomodulatory and antioxidant effects and their ability to modulate the gut microbiota. Mushrooms can become abundant in organic selenium when grown under certain conditions. The present study aimed to determine the optimum Se level, using Se-enriched mushrooms and selenite, in weaned pig diets to enhance intestinal health, performance and antioxidant capacity. Our study demonstrated that 0.3 ppm selenium inclusion, using selenium-enriched mushroom powder, led to positive effects on faecal scores and had similar pig performance compared to zinc oxide during the first 21 days post-weaning. The selenium inclusion level of 0.6 ppm, using selenium-enriched mushroom powder and selenite, enhanced pig performance and aspects of gastrointestinal health during days 21 and 39 post-weaning.This study was conducted to examine the effects of varying selenium (Se) inclusion levels, in the form of Se-enriched mushroom powder (SeMP) and selenite, on post-weaning growth performance (Period 1; day 1–21), intestinal health and antioxidant capacity (Period 2; day 21–39). Weaned pigs were blocked according to live weight, sex and litter of origin and randomly assigned to the following experimental groups: basal (basal + selenite (0.3 ppm Se)); ZnO (basal + ZnO + selenite (0.3 ppm Se)); 0.15 SeMP (basal + SeMP (0.15 ppm Se)); 0.3 SeMP (basal + SeMP (0.3 ppm Se)) and 0.6 SeMP/Sel (basal + SeMP (0.3 ppm Se) + selenite (Sel) (0.3 ppm Se)) with eight replicates/experimental group. After 21 days, the ZnO experimental group was removed from the experiment and the remaining pigs continued on their respective diet until day 39 post-weaning (Period 2). In Period 1, 0.15 SeMP supplementation reduced (p < 0.05) average daily gain (ADG), average daily feed intake (ADFI) and day 21 body weight, and increased (p < 0.05) faecal scores compared to the ZnO group. Supplementation with 0.3 SeMP and 0.6 SeMP/Sel during Period 1 resulted in similar (p > 0.05) ADG, ADFI, gain-to-feed ratio (G:F) and body weight compared to the ZnO group. However, 0.6 SeMP/Sel supplementation increased (p < 0.05) faecal scores compared to the ZnO group. In Period 2, 0.6 SeMP/Sel increased (p < 0.05) ADG, feed efficiency and day 39 body weight compared to the basal group. Supplementation with Se-enriched mushroom powder, at all inclusion levels, increased (p < 0.05) the abundance of Prevotellaceae and Prevotella, decreased (p < 0.05) the abundance of Sporobacter and increased (p < 0.05) the expression of SELENOP in the jejunum compared to the basal group. Lactobacillaceae and Lactobacillus was increased (p < 0.05) in 0.15 SeMP and 0.3 SeMP pigs compared to the basal group. Selenium deposition in muscle and liver tissue increased (p < 0.001) as a function of inclusion level while pigs supplemented with 0.3 ppm organic Se (0.3 SeMP) had an increase (p < 0.05) in total Se in the muscle compared to pigs supplemented with 0.3 ppm inorganic Se (basal). In conclusion, 0.3 SeMP supplementation led to positive effects on faecal scores and had similar pig performance compared to ZnO in Period 1, while the addition of 0.3 ppm selenite to 0.3 SeMP (0.6 SeMP/Sel) in Period 2 led to enhanced pig performance and aspects of gastrointestinal health.

Single-atom scale metal vacancy engineering in heteroatom-doped carbon for rechargeable zinc-air battery with reduced overpotential

Metal-air batteries have drawn great attention in the past decade due to their high energy density and low cost. However, several challenges remain in the development of such promising devices, including slow kinetics of the cathodic reaction and undesirable deposition of metal oxide on air cathode. Herein, as a proof of concept, we show single-atom scale metal vacancy engineering in heteroatom-doped carbon cathode to enable high-performance zinc-air battery with reduced overpotential. Density functional theory calculations indicate that metal vacancy-induced pyridinic-N can tailor the electronic structure and thus facilitate the catalytic reaction. The single-atom dispersed Fe–N–C catalyst with optimized Fe vacancies shows improved reactivity and the facilitated chemisorption of oxygen intermediates in the actual battery operation is directly observed by in-situ X-ray diffraction characterization. Moreover, the in-situ observation also indicates the absence of zinc oxide, which can be ascribed to strong Lewis basicity created by pyridinic-N that effectively prevents the access of zincate ions with negative charge and thus enables non-deposition of zinc oxide. Applying this strategy, the rechargeable zinc-air battery shows high reversibility and stability over 1000 cycles with negligible voltage gap change of only 0.04 V. This work not only affords valuable insights but also opens up new perspectives to develop high-performance metal-air batteries.

Investigation on the Influence of Various Kinds of Soaps on the Mechanical Properties of Silica Filled Composites Based on Natural Rubber

The aim of this study was to investigate the influence that different fatty acid zinc salts had on the rheological, curing and mechanical properties of natural rubber based composites filled with silica and containing bi-functional organosilanes in the presence or absence of zinc oxide. The results demonstrated that the combination of zinc oxide and zinc soaps had a strongly pronounced anti-reversion effect. The absence of reversion in the cure curves of the rubber compounds comprising a combination of zinc oxide, stearic acid and zinc soaps, results in retention of their mechanical properties, even after overcure.

Buffer layers in inverted organic solar cells and their impact on the interface and device characteristics: An experimental and modeling analysis

Buffer layers play crucial role in increasing the power conversion efficiencies (η) in organic solar cells (OSCs) and hence it is important to understand the underlying microscopic mechanisms behind the improvements aiding the existing qualitative understanding. In this manuscript, we have investigated the role of zinc oxide (ZnO) and molybdenum oxide (MoO3) buffer layers on the current density - voltage (J-V) characteristics of inverted organic solar cell (IOSC) devices combining experimental results with drift-diffusion based transport modeling, on the active layer (ActL) blend of P3HT:PCBM (Poly 3-hexylthiophene (P3HT): (6, 6) phenyl C61 butyric acid methyl ester (PC61BM)), a workhorse system with well-established device data. The results show that while ZnO alone improves the open circuit voltage (VOC) significantly, use of both the ZnO and MoO3 layers help in improving the short-circuit current density (JSC), aided by contributions to exciton dissociation by both layers at the electrode ActL interface. Absence of ZnO, in particular, causes S-shaped J-V curve which is attributed to reduced surface recombination velocity of majority carriers due to hindered charge extraction and non-selectivity of carrier flow towards cathode. On the other hand, presence of MoO3film between ActL and the anode assists in making an energetically favourable contact with ActL and improves the extraction of photo generated charge carriers. Further in conjunction with dark J-V characteristics, impedance spectroscopy (IS) carried out under dark and illuminated conditions establishes the role of buffer layers in modifying the barrier heights at the contacts and the interfacial structure.

Expression of Zinc Transporter Genes in Rice as Influenced by Zinc-Solubilizing Enterobacter cloacae Strain ZSB14.

Zinc (Zn) deficiency in major food crops has been considered as an important factor affecting the crop production and subsequently the human health. Rice (Oryza sativa) is sensitive to Zn deficiency and thereby causes malnutrition to most of the rice-eating Asian populations. Application of zinc solubilizing bacteria (ZSB) could be a sustainable agronomic approach to increase the soil available Zn which can mitigate the yield loss and consequently the nutritional quality of rice. Understanding the molecular interactions between rice and unexplored ZSB is useful for overcoming Zn deficiency problems. In the present study, the role of zinc solubilizing bacterial strain Enterobacter cloacae strain ZSB14 on regulation of Zn-regulated transporters and iron (Fe)-regulated transporter-like protein (ZIP) genes in rice under iron sufficient and deficient conditions was assessed by quantitative real-time reverse transcription PCR. The expression patterns of OsZIP1, OsZIP4, and OsZIP5 in root and shoot of rice were altered due to the Zn availability as dictated by Zn sources and ZSB inoculation. Fe sufficiency significantly reduced the root and shoot OsZIP1 expression, but not the OsZIP4 and OsZIP5 levels. Zinc oxide in the growth medium up-regulated all the assessed ZIP genes in root and shoot of rice seedlings. When ZSB was inoculated to rice seedlings grown with insoluble zinc oxide in the growth medium, the expression of root and shoot OsZIP1, OsZIP4, and OsZIP5 was reduced. In the absence of zinc oxide, ZSB inoculation up-regulated OsZIP1 and OsZIP5 expressions. Zinc nutrition provided to the rice seedling through ZSB-bound zinc oxide solubilization was comparable to the soluble zinc sulfate application which was evident through the ZIP genes’ expression and the Zn accumulation in root and shoot of rice seedlings. These results demonstrate that ZSB could play a crucial role in zinc fertilization and fortification of rice.

Synthesis and characterization of chlorapatite–ZnO composite nanopowders

The influence of zinc oxide content on the formation of chlorapatite-based composite nanopowders in the mechanically alloyed CaO–CaCl2–P2O5–ZnO system was studied. To mechanosynthesize composite nanopowders, different amounts of hydrothermally synthesized zinc oxide nanoparticles (0–10wt%) were mixed with ingredients and then were mechanically activated for 5h. Results showed that in the absence of zinc oxide, high crystalline chlorapatite nanopowder was obtained after 5h of milling. In the presence of 4 and 7wt% zinc oxide, the main product of milling for 5h was chlorapatite–zinc oxide composite nanopowder. On increasing the zinc oxide content to 10wt%, composite nanopowder was not formed due to improper stoichiometric ratio of the reactants. The crystallite size, lattice strain, volume fraction of grain boundary, and crystallinity degree of the samples fluctuated significantly during the milling process. In the presence of 7wt% zinc oxide, the crystallite size and crystallinity degree reached 51±2nm and 79±2%, respectively. During annealing at 900°C for 1h, the crystallization of composite nanopowder occurred and as a result the crystallinity degree rose sharply to 96±3%. In addition, the crystallite size increased to 77±2nm after annealing at 900°C. According to SEM and TEM images, the composite nanopowder was composed of both ellipse-like and polygonal particles with a mean size of about 98nm.

Pre-Vulcanization Inhibition of a N-t-Butyl-2-Benzothiazole Sulfenamide Cure by N-(Cyclohexylthio)Phthalimide

Abstract The reactions of N-(cyclohexylthio)phthalimide (CTP), in the absence of zinc oxide, leading to the inhibition of vulcanization in a N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerated sulfur cure were studied in the presence and absence of rubber. Mixtures of CTP, TBBS and sulfur were heated in a DSC and the reaction products and residual curatives analyzed by HPLC. Cyclohexanethiol, a decomposition product of CTP, reacted with TBBS producing 2-mercaptobenzothiazole (MBT) and t-butylamine, both of which reacted with CTP. In a polyisoprene compound, the addition of CTP did not delay the formation of the initial crosslinks, however the crosslink density did not increase substantially until the CTP had been consumed. MBT, a product of the crosslinking reaction, reacted preferentially with the CTP and not the TBBS. In the absence of CTP, the MBT was shown to accelerate the rate of TBBS polysulfide formation leading to a rapid rise in crosslink density.

Effects of organic nucleating agents and zinc oxide nanoparticles on isotactic polypropylene crystallization

Organic nucleating agents and inorganic nanoparticles, as well as their hybrid composites, affect the crystallization temperature and morphology of the monoclinic α-form of isotactic polypropylene (iPP). Techniques such as differential scanning calorimetry, hot-stage optical microscopy with cross polars, wide angle X-ray diffraction, and transmission electron microscopy were employed. Nanoparticles of zinc oxide function as efficient supports for 1,3,5-benzene tricarboxylic-( N -2-methylcyclohexyl)triamine because the temperature at which the maximum rate of iPP crystallization occurs during 10 °C/min cooling from the molten state increases from 111 °C for the pure polymer to 125 °C at low concentrations of this hybrid nucleating agent. In the absence of zinc oxide, 0.06 wt% of this aliphatic triamine recrystallizes near 165 °C and increases the crystallization temperature of iPP by 7 °C, relative to the pure polymer. Fluorinated aromatic triamines, such as 1,3,5-benzene tricaboxylic-( N -4-fluorophenyl)triamine, are weak nucleating agents that reduce spherulite size in isotactic polypropylene but only increase the crystallization temperature marginally when the polymer is cooled from the molten state. Both micro- and nanoparticles of zinc oxide reduce spherulite size in isotactic polypropylene, but smaller spherulites are observed when the inorganic nanoparticles exhibit dimensions on the order of 40–150 nm relative to micron-size particles. In contrast, 0.06 wt% of the aliphatic triamine in iPP yields a distorted birefringent texture under cross polars that is not spherulitic. Non-spherulitic birefringent textures in iPP are also observed when the aliphatic triamine nucleating agent is coated onto micro- or nanoparticles of zinc oxide. This study demonstrates that the nonisothermal crystallization temperature of isotactic polypropylene increases by an additional 7 °C when an aliphatic triamine is distributed efficiently within the polymeric matrix by coating this nucleating agent onto zinc oxide nanoparticles.

Effects of organic nucleating agents and zinc oxide nanoparticles on isotactic polypropylene crystallization

Organic nucleating agents and inorganic nanoparticles, as well as their hybrid composites, affect the crystallization temperature and morphology of the monoclinic α-form of isotactic polypropylene (iPP). Techniques such as differential scanning calorimetry, hot-stage optical microscopy with cross polars, wide angle X-ray diffraction, and transmission electron microscopy were employed. Nanoparticles of zinc oxide function as efficient supports for 1,3,5-benzene tricarboxylic-( N-2-methylcyclohexyl)triamine because the temperature at which the maximum rate of iPP crystallization occurs during 10 °C/min cooling from the molten state increases from 111 °C for the pure polymer to 125 °C at low concentrations of this hybrid nucleating agent. In the absence of zinc oxide, 0.06 wt% of this aliphatic triamine recrystallizes near 165 °C and increases the crystallization temperature of iPP by 7 °C, relative to the pure polymer. Fluorinated aromatic triamines, such as 1,3,5-benzene tricaboxylic-( N-4-fluorophenyl)triamine, are weak nucleating agents that reduce spherulite size in isotactic polypropylene but only increase the crystallization temperature marginally when the polymer is cooled from the molten state. Both micro- and nanoparticles of zinc oxide reduce spherulite size in isotactic polypropylene, but smaller spherulites are observed when the inorganic nanoparticles exhibit dimensions on the order of 40–150 nm relative to micron-size particles. In contrast, 0.06 wt% of the aliphatic triamine in iPP yields a distorted birefringent texture under cross polars that is not spherulitic. Non-spherulitic birefringent textures in iPP are also observed when the aliphatic triamine nucleating agent is coated onto micro- or nanoparticles of zinc oxide. This study demonstrates that the nonisothermal crystallization temperature of isotactic polypropylene increases by an additional 7 °C when an aliphatic triamine is distributed efficiently within the polymeric matrix by coating this nucleating agent onto zinc oxide nanoparticles.

Some Aspects on the Crosslink Reaction of Natural Rubber with Dipentamethylene Thiuram Tetrasulfide

Abstract The mechanism of vulcanization of natural rubber with the sulfurating agent dipentamethylene thiuram was studied. On the transformation from crosslink precursor to crosslink, the route via disproportionation is preferred. In the presence or absence of zinc oxide and stearic acid as activators, the formation of the crosslink precursor follows similar processes, while the main difference is in the reaction induction times. In addition, the desulfuration reaction was favored by the presence of zinc oxide.

Analysis of the Mechanism of N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene

Abstract Results of previously published work involving network analysis and accelerator intermediate analysis of cis-polyisoprene were compared to help correlate and rationalize network/chemistry relationships. Both classical chemical probe network analysis and further NMR measurements (DEPT analysis) were used as necessary to verify NMR peak assignments. Furthermore, samples of the conventional formulation were vulcanized in the absence of zinc oxide and stearic acid to help elucidate the role of zinc in the vulcanization process. Polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic substituted cis-polysulfides both with and without double bond migration, while zinc polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic cis and trans polysulfides substituted structures with no double bond migration. Polysulfidic substitution on the isoprene methyl carbon was shown to result from exchange reactions during network maturation. The network-chemistry relationships were compared with earlier mechanistic studies and several points of agreement were noted.

ChemInform Abstract: STUDIES OF THE PYROLYSIS OF DIETHYLZINC BY THE TOLUENE CARRIER METHOD AND OF THE REACTION OF ETHYL RADICALS WITH TOLUENE

The thermal decomposition of diethylzinc in a toluene carrier system has been studied over the temperature range of 669 to 762 K, and percent decomposition of 3.8 to 97.2%. The decomposition occurs by a two step mechanism, the second step rapidly following the first,The overall progress of the reaction was followed by determination of the residual diethylzinc by hydrolysis followed by analysis for zinc by atomic absorption. In selected runs two additional methods were used: (i) measurement and analysis of the gas evolved during the hydrolysis and (ii) full analysis of all pyrolysis products involving the C2H5 group.In the absence of zinc oxide the decomposition is essentially homogeneous andor −205 000/19.15T if the activation energy is expressed in joules rather than calories. The presence of zinc oxide causes marked catalysis of the overall decomposition but does not appear to affect reaction 3 or reaction 6.Reaction 6 is in a strongly pressure dependent region and is based on very limited data.

The Chemistry of Sulfur Curing. III. Effects of Zinc Oxide on the Mechanism of the Reaction of Cyclohexene with Sulfur

Abstract Reaction of cyclohexene and sulfur at 140° followed by lithium aluminum hydride reduction of the polysulfide products results in the formation of cyclohexanethiol, 2-cyclohexene-1-thiol, cis- and trans-1, 2-cyclohexanedithiol, and cyclohexyl sulfide. If zinc oxide is present during the reaction, trans-1, 2-cyclohexanedithiol is the major product. In the absence of zinc oxide, cis-1, 2-cyclohexanedithiol is the major product. It is postulated that in the absence of zinc oxide the reaction proceeds via a free radical chain involving polysulfenyl radicals accompanied by a secondary polar addition reaction of hydrosulfide products with cyclohexene. Zinc oxide when present is postulated to initiate an ionic chain reaction which, due to its greater velocity, dominates the radical chain reaction.

Kinetics of accelerated vulcanization. Sulfur vulcanization accelerated with 2‐mercaptobenzothiazole and its zinc salt in presence of zinc oxide and zinc oxide and stearic acid

AbstractSulfur vulcanization of natural rubber (NR) and styrene‐butadiene rubber (SBR) accelerated with 2‐mercaptobenzothiazole and zinc oxide with or without stearic acid has been studied and the results compared with those obtained by replacing the thiazole with its zinc salt. The order of the rate of vulcanization as measured from free sulfur decrease or crosslink formation is observed to be unity with respect to time and less than one with respect to accelerator concentration. In absence of stearic acid, the zinc salt is much less efficient than the thiazole in promoting vulcanization, and the efficiency of the latter shows a noticeable improvement over what is attained in absence of zinc oxide. Addition of stearic acid not only raises the efficiency of both the systems to the same level but also leads to a faster rate of vulcanization, a much higher degree of crosslinking, avoidance of reversion, and production of vulcanizates with considerably improved mechanical properties. The formation of zinc sulfide also reveals interesting variation. Attempts have been made to interprete these results in terms of complex formation between zinc salt of thiazole and zinc stearate.

The Chemistry of Vulcanization. VIII. Role of Zinc Butyrate in the Reaction of Diphenylmethane, Sulfur and 2-Benzothiazolyl Disulfide

Abstract Diphenylmethane (DPM) which contains α-methylenic hydrogen has been used as a model of rubber hydrocarbon, and reactions involving DPM, sulfur and thiazole type accelerators in the absence of zinc oxide or soap were reported in previous papers. These papers reported that 2-mercaptobenzothiazole (MBT), 2-benzothiazolyl disulfide (MBTS) and zinc salt of 2-mercaptobenzothiazole (ZMBT) generate the same radical, i.e., 2-benzothiazolesulfenyl which has the accelerating effect. This radical opens the ring of elementary sulfur and thus accelerates vulcanization since the spontaneous splitting of the sulfur ring molecule to a biradical was found to be the rate determining step in the reaction of DPM with sulfur alone. Processes by which accelerators generate this radical differ from each other owing to the types of accelerators, that is, mercaptan, disulfide and zinc mercaptide type. The previous paper reported the reaction involving DPM, sulfur and MBT in the presence of zinc butyrate. According to this, MBT first reacts with zinc butyrate to form butyric acid and ZMBT, the latter then generating the effective benzothiazole-sulfenyl radical. Thus, even in the presence of zinc soap, the essential mechanism of acceleration is the same as in the absence of zinc soap, though the process and rate for forming benzothiazolesulfenyl radical are different in the absence of zinc soap. In the present paper the reaction of DPM, sulfur and MBTS in the presence of zinc butyrate are reported. The reaction mechanism will be deduced from the experimental results obtained here and from conclusions obtained in the previous papers. The rate equation for MBTS consumption and equation for the accelerating efficiency for this accelerator are derived from the mechanism. The theoretical equations were examined by experiments.

The Reaction of Tetramethylthiuram Disulfide and Monosulfide with Rubber

Abstract The kinetics of the reaction of tetramethylthiuram monosulfide (TMTM) differ from that with the disulfide (TMTD). No formation of chemical crosslinks takes place; the sulfur of TMTD adds in correspondence with a curve exhibiting no maximum and the addition differs in the presence and absence of zinc oxide. Simultaneously, the thermal decomposition of TMTM takes place. The electron paramagnetic resonance spectra and the reaction with geraniol show TMTD and TMTM to interact with rubber through a free radical stage.

Metal Oxides in Tetramethylthiuram Disulfide Vulcanization

Abstract Rubber is usually vulcanized with the aid of the so-called activators, metal oxides, zinc oxide being the one most often used. In vulcanization in the presence of MBT (mercaptobenzothiazole) or DPG (diphenylguanidine) as accelerators it was found that vulcanization activators have almost no effect on the rate of addition of sulfur to rubber, but have a significant influence on the rate and degree of crosslinking of the rubber molecules. Special interest attaches to studies of the action of metal oxides in vulcanization with tetramethylthiuram disulfide (TMTD), as it is known from actual practice that in the absence of zinc oxide this accelerator does not bring about vulcanization. Vulcanization with TMTD was studied on mixtures of natural rubber (extracted with cold acetone in a stream of nitrogen for 50 hours) and of synthetic isoprene rubber (SKI) masticated on microrolls, of the following compositions (in parts by weight).

The Chemistry of Vulcanization. VII. Role of Zinc Butyrate in the Reaction of Diphenylmethane, Sulfur and 2-Mercaptobenzothiazole

Abstract In previous Parts of this series, the accelerating mechanism of thiazole type accelerators, namely, 2-mercaptobenzothiazole (MBT), 2,2′-benzothiazolyl disulfide (MBTS) and zinc salt of 2-mercaptobenzothiazole (ZMBT) in the absence of zinc oxide or zinc soap, was investigated with diphenylmethane (DPM) as a model compound of rubber hydrocarbon. The significance of DPM as a model was discussed in some of the earlier papers. Parts IV, V and VI of this series indicated that 2-mercaptobenzothiazolyl radical generated from accelerators splits the sulfur ring, and that the processes by which accelerators generate the radical differ with each other according to their types. These results were obtained in the absence of zinc oxide or zinc soap. The present study will report the role of zinc butyrate in the reaction involving DPM, sulfur and MBT. Experience in the industry indicates that zinc oxide (or zinc soap) is indispensable to the thiazole type accelerators and that the efficiency of zinc oxide or soap is more prominent in MBT than in MBTS or ZMBT. The results obtained in the previous papers also suggest that zinc oxide or soap may have an influence on the rate at which the accelerator generates 2-mercaptobenzothiazolyl radical, since it is shown in Parts IV, V and VI that the radical has an accelerating effect. Therefore, it may be considered that zinc oxide or zinc soap activates MBT more effectively than does the other thiazole type accelerators in order to produce this radical. As will be seen later in this study, interaction of MBT with zinc butyrate in the absence of sulfur produces ZMBT and butyric acid. The ZMBT will interact with sulfur and generate the 2-mercaptobenzothiazolyl radical as reported in Part VI. The zinc salt thus formed will be dispersed in a state of molecular dispersion in the reaction system, while the same compound prepared in Part VI was not dissolved in DPM even at the reaction temperatures. In this respect the former is considered more effective than the latter. In order to verify the above assumptions the reaction involving DPM, sulfur and MBT in the presence of zinc butyrate were investigated. The reaction products and mechanism were compared with those in the absence of zinc soap. Since zinc butyrate is soluble in the reaction system at the reaction temperatures, a kinetic study also was carried out and compared with that in the absence of zinc soap.