bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactively Curable Rubbers—I: Diene Elastomers with Pendant Isocyanate and/or Hydroxyl Functionality
Authors: Parker Dane K. , Colvin Howard A. , Weinstein Arthur H. , Chen Sun-Lin 
Published: February 2011

Abstract
In conclusion, we have demonstrated that modified diene elastomers containing active hydrogens and/or blocked-isocyanate derivatives can be crosslinked (cured) by three distinct methods. These methods include: 1. reaction of polymer-bound active hydrogens with monomeric polyisocyanates (Type I), 2. reaction of polymer-bound isocyanates with compounds containing two or more active hydrogens (Type II), and 3. reaction between polymer segments that contain both polymer-bound isocyanates and active hydrogens (Type III). Additionally, we have shown that the new polymerizable blocked-isocyanate derivatives (Type II and III systems) can be readily incorporated into SBR and NBR elastomers by standard emulsion-polymerization techniques. The degree and distribution of these monomers within the elastomer matrix were shown to be controlled by knowledge of their reactivity ratios. Furthermore, we have shown that the processing and properties of these systems can be readily controlled by the proper combination of isocyanate blocking group, active-hydrogen component, and catalyst. In many cases, these modified elastomers can be coagulated, dried, compounded, and cured using methods common to the rubber industry. Although not optimized, we have also shown that useful vulcanizates can be produced from extremely simple recipes. Conventional acceleration systems e.g., sulfur, accelerator, zinc oxide, are eliminated. The resulting urethane or urea crosslinks are remarkably durable under both thermal and hydrolytic conditions. Obviously, the possibilities for these uniquely reactive elastomers have not been exhausted. Many other intriguing applications of this technology are currently being explored. These applications will be the subject of future publications.
New Elastomers by Reactive Processing. Part I. Vulcanizable Precured Alloys from NBR and ACM
Authors: Coran A. Y. 
Published: February 2011

Abstract
The dynamic vulcanization of ACM (the dispersed phase) during its mixing with NBR (the continuous phase) can produce a new type of millable specialty elastomer alloy. The millable dynamic vulcanizate containing the crosslinked dispersed phase can be later mixed with curatives for the continuous phase, fillers, antidegradants, etc. The completed mixture of millable dynamic vulcanizate with the additional curatives (for the NBR), fillers, stabilizers, etc. can then be vulcanized e.g., in a heated mold. Thus, the dynamic vulcanization technique is a means of separately controlling the vulcanization of individual phases of a blend of elastomers. Since the ACM can be completely vulcanized during the dynamic vulcanization stage of the mixing process, the usual postcuring associated with ACM technology is not necessary. Also, since the continuous or external phase is NBR, the prevulcanized millable alloy exhibits processability more similar to that of NBR than to that of ACM. Sticking and splitting on the roll mill is less of a problem after dynamic vulcanization than before dynamic vulcanization. The dynamic vulcanization of the ACM can be achieved by using the soap-sulfur type or the diamine-generator type curatives during the mixing process at elevated temperatures. Compositions filled either with carbon black (N326) or silica (Hisil 233) give compositions of excellent hot-oil resistance and room-temperature set. (Compression-set testing has not yet been done at this early stage of our research.) As in the case of conventional NBR stocks, the silica-filled compositions give excellent hot-air resistance whereas, carbon-black-filled compositions give fair hot-air resistance. In either the black-filled or the silica-filled compositions, provided that at least half of the rubber polymer is ACM, essentially complete resistance to ozone attack is obtained.
Effect of Contact Time on Tack
Authors: Gent A. N. , Kim H. J. 
Published: February 2011

Abstract
The following conclusions are obtained: 1. The autohesion strength of elastomers increases linearly with the rate of detachment over the range 200 to 1000 mm/s. 2. The autohesion strength increases by a factor of only 2× to 3× when the contact pressure is increased by 3 orders of magnitude, from 2 kPa to 2 MPa. 3. Autohesion strength develops rapidly in the early stages of contact for SBR, BR, and EPR, increasing from about 20 J/m2 to about 500–1000 J/m2 as the contact time increased from 1 to 100 ms. It increased more slowly thereafter, to about 10 kJ/m2 after a contact time of 1000 s. 4. The development of autohesion was exactly the same at 3°C as at 25°C. This feature is attributed to simultaneous changes in developing true contact, and in resisting separation after contact, that exactly cancel. 5. Adhesion between SBR and EPR is lower than the autohesion strength of the individual polymers over the whole range of contact time. On the other hand, the three strengths for SBR and BR are almost the same. 6. The overall similarity between the rates of development of autohesion and adhesion suggest that autohesion is governed mainly by the strength and extent of intimate molecular contact that is developed at the interface. Contributions from interdiffusion, if any, appear to be significant only in the later stages of contact.
Grafting of Waste Rubber
Authors: Adam G. , Šebenik A. , Osredkar U. , Veksli Z. , Ranogajec F. 
Published: February 2011

Abstract
By the redox method and by gamma irradiation, it was possible to graft ethyl acrylate on to granulate of waste rubber. The quantity of grafted monomer was larger when gamma irradiation was used. When combining ethyl acrylate with 5-methylene-2-norbornene in the redox system with the intention to introduce more double bonds in the grafted granulate, it was found that norbornene does not participate in the reaction and that it even prevents the grafting of ethyl acrylate. This is just a part of extensive experimental work which was done with the intention to chemically modify the rubber granulate for the purpose of enlarging the quantity of waste rubber to be possibly reused in the rubber industry.
Surface Treatments to Reduce Friction: Rubber Glove Applications
Authors: Roberts A. D. , Brackley C. A. 
Published: February 2011

Abstract
The frictional properties of rubber surfaces modified by various treatments have been investigated in order to understand the factors which reduce the friction and give the surface appropriate qualities for practical use. The study was in two stages. Initial measurements were made on thin sheets of hot-vulcanized natural rubber; then followed tests on latex glove material to see how the initial results and understanding related to the application. Measurements of friction coefficient were made against a wavy glass plate, giving reproducible results, and against finger skin. Supplementary measurements were made of surface roughness and hardness, liquid contact angle, and water absorption. Factors of importance in the reduction of dry friction were found to be an increased surface roughness and hardness. In practice, difficulties may be experienced under slightly wet or damp conditions, which can increase the friction above the dry value. Here it was found to help if the surface treatment could absorb water. For surgeons' gloves in contact with moist skin, one particular treatment, a hydrogel polymer coating, gave the necessary surface roughness, hardness, and water absorptivity, making the gloves easy to don and pleasant to wear.
Characteristic Ratio and Plateau Modulus of 1,2-Polybutadiene. A Comparison with Other Rubbers
Authors: Roovers Jacques , Toporowski Paul M. 
Published: February 2011

Abstract
In the course of work on linear and ring polybutadienes with 62% 1,2 units, a number of discrepancies were noted with data on polybutadienes of various microstructure available in the literature. For example, GNο=870 kPa for our 62% 1,2-polybutadiene. This is larger than GNο=730 kPa for a 56% 1,2-polybutadiene and GNο=550 kPa for a 78% 1,2-polybutadiene sample. The cis : trans ratio of our 62% 1,2-polybutadiene, prepared with potassium counterion, is 1 : 4, On the other hand, the cis : trans ratio of 62% 1,2-polybutadiene prepared with a modified Li catalyst is estimated to be 1 : 2. It is conceivable that the different cis : trans ratio leads to different properties at constant 1,2 content. Nevertheless, the low levels of both the cis and the trans units are not expected to cause more than minor differences in the properties of the polybutadienes. Correct values for GNο of model polymers are important for the study of the influence of the chemical structure on the melt characteristics of a polymer. For this reason, it was thought useful to reinvestigate 1,2-polybutadiene itself in some detail. The synthesis of narrow molecular-weight distribution 1,2-polybutadiene by anionic polymerization techniques has been described recently. The dilute-solution properties of 1,2-polybutadiene has been investigated. The melt rheology of two 1,2-polybutadiene samples have been studied, but no systematic study of the molecular-weight dependence of the melt properties was made. 1,2-Polybutadiene has been used as a component in block copolymers with 1,4-polybutadiene. These studies have permitted an investigation of the phase behavior of two rubbery blocks at room temperature. Poly(l,4-butadiene-graft-l,2-butadiene)s with well-defined composition and architecture have also been prepared. Hydrosilylated 1,2-polybutadiene has found use as the coupling agent for multiarm star polymer, and this method can easily be extended to the preparation of poly( l,2-butadiene-graft-l,4-butadiene). Hydrogenated 1,2-polybutadienes are prepared as model polymers for poly(l-butene). The synthesis and characterization of a series of 1,2-polybutadienes are described here. Special attention is given to low-molecular-weight polymers. The linear viscoelastic properties of the melts are also described. In the discussion, the relation between the characteristic ratio, C∞, and the plateau modulus, GNο, of a number of model polymer systems is explored.
The Resolution of Elastomer Blend Properties by Stress-Strain Modelling. An Extension of the Model to Carbon-Black-Loaded Elastomers
Authors: Bauer R. F. , Crossland A. H. 
Published: February 2011

Abstract
The unique stress-strain behavior of a carbon-black-loaded elastomer is due to the presence of a rigid, particulate phase, but also to the interaction of the elastomer chains with the filler. It is postulated that this interaction takes the form of adsorption on the filler-particle surface, which results in trapped entanglements. Upon deformation, the trapped chains are aligned parallel to the axis of stress. Thus, a practical stress-strain relationship could be developed which is capable to model the stress-strain behavior of compounds over the full range of extensions up to break. The analysis of a highly prestrained carbon-black-loaded NR compound in which the entanglement effect had been mechanically destroyed, demonstrated that the “sea-island” (SIP) coupling arrangement is most suitable for accounting for the interaction effect of the elastomer and carbon black. For moderately prestrained carbon-black-loaded NR and BR compounds a good fit of theory to experiment is obtained for a combination of the SIP coupling arrangement and the specially derived stress-strain relationship. Thus, a practical method is available for describing the deformation of carbon-black-loaded elastomers and for the modelling of carbon-black-loaded elastomer blends.
Mechanical Properties of Vulcanizates Containing Covalent, Ionic, and Mixed Crosslinks
Authors: Hamed Gary R. , Han K. T. 
Published: February 2011

Abstract
Vulcanization by peroxide and sulfur are the two common methods to crosslink diene elastomers. Crosslinks using peroxide are simple carbon-carbon covalent bonds, whereas, with sulfur, a distribution of sulfur linkages, Sx, of various rank, x, may be present. Networks in which x=1 exclusively are said to be monosulfidic; these, as well as peroxide-cured vulcanizates, possess low-set characteristics, low stress relaxation, and good resistance to aging—all evidence of the permanence of C-S-C and C-C linkages. On the other hand, when x is large, the networks are termed polysulfidic; stress relaxation and set are higher, while resistance to aging (network stability) is poorer compared to rubbers with monosulfidic or carbon covalent linkages. It has been proposed that these properties result from the relative weakness of polysulfide bonds, which can break and reform under load. In applications such as tires, where resistance to fracture under severe loads is required, accelerated-sulfur vulcanization with sulfur is the preferred method of crosslinking. These networks are neither completely monosulfidic nor fully polysulfidic, but rather contain a mixture of weak and strong crosslinks. The distribution depends on the type and level of accelerator, the sulfur concentration, and the curing conditions. It is quite difficult to characterize this distribution, or even approximately to infer it from the complex chemistry of sulfur vulcanization. Trial and error methods, over the years, have led to optimized compositions. Vulcanizates with the appropriate mix of crosslink types have superior strength and fatigue resistance compared to networks containing only permanent links, i.e., carbon-carbon covalent or monosulfidic. Perhaps the important feature which has allowed sulfur vulcanization to remain the dominant crosslinking method for over 100 years is the presence of crosslinks with varying strength.
Multifunctional Activities of Benzazole Derivatives in Rubber Vulcanization
Authors: Khanra Tapan Kumar , Adhikari Basudam , Maiti Sukumar 
Published: February 2011

Abstract
Benzazole thiol (e.g. 2-Mercaptobenzothiazole and 2-Mercaptobenzimidazole) and sulfenamide (e.g. 2-Morpholino thiobenzothiazole) are used as rubber chemicals. The nature and the extent of their performances in rubber depend on the nature of the key heteroatom present in the azole ring. It has been found that the presence of X (S or N) as the key heteroatom in the grouping —X—‖—SH of the azole ring is responsible for either accelerator or antioxidant action. Although some scattered informations on accelerator and antioxidant functions are available for some of the benzazole derivatives, their comparative ratings in these functions are not found in the literature. In the present communication, synthesis and characterization of some benzazole sulfenamides are reported. Together with this, a comparative evaluation of accelerator-cum-anti-oxidant properties of both the benzazole thiols and sulfenamides is described. Such dual function rubber chemicals are unusual and novel and should fetch a premium price as rubber additives.
The Influence of Fumed Silica Properties on the Processing, Curing, and Reinforcement Properties of Silicone Rubber
Authors: Cochrane H. , Lin C. S. 
Published: February 2011

Abstract
The present study uses a commercial heat cured silicone rubber formula (including a process aid) and mixing techniques to investigate the effect of varying fumed silica properties—including load, surface area, silica structure level, and surface pretreatment levels—on the rubber processing, curing, and cured physical properties. Based on the results, a simple silica network reinforcement model was developed to explain the changes in processing, curing, and vulcanizate properties of the silicone elastomers. The network is held together by silica-silica interactions and silica-polymer-silica bridge bonds between the silica aggregates. Increasing the silica loading, surface area, and structure level increases the number of interactions and hence the network strength. The pretreatment of the silica surface with organosilane molecules reduces the strength of silica-silica and silica-polymer interactions, therefore, weakening the silica network. Furthermore, the good interrelations between the initial plasticity, crepe hardening, curing, modulus yield, and durometer values strongly supports the concept of the presence of a silica network within the compounds under the low strain conditions of the tests.
Solid State C-13 NMR Studies of Vulcanized Elastomers. XII. Accelerated Sulfur-Vulcanized High-Vinyl Polybutadiene
Authors: Rana M. A. , Koenig J. L. 
Published: February 2011

Abstract
Solid state 13C NMR measurements were made on accelerated sulfur-vulcanized polybutadiene with a high vinyl content (70%). The systems studied included conventional, semi-efficient and efficient formulated with N-t-butyl benzothiazole sulfenamide (TBHS) as the accelerator. The kinetics of the three vulcanization systems were different, but the final levels of cure were similar. The resonances due to TBBS disappear as the vulcanization proceeds. The ratio of monosulfidic to polysulfidic crosslinks as a function of accelerator to sulfur ratio initially decreases rapidly and then increases in favor of the monosulfidic component. A variety of sulfur-bonded accelerator fragments was found in the system. This reinforces the polar-radical mechanism.
The Development of Elastomer Rheological Processability Quality Control Instruments
Authors: White James L. , Soos Istvan 
Published: February 2011

Abstract
We have surveyed the development of processability measurements from its origins, about 1920, to the present. We have followed the factors—technology, scientific, and political—which have caused its evolutions. The earliest instruments the capillary and compression rheometer, are still with us. As early as the mid 1930s, different traditions developed in the United States and Germany, differences which continue to the present day. These were accentuated by the development of synthetic rubber and World War II. The Germany industry used the Defo compression instrument and the Americans decided on the Mooney shearing disc viscometer. The early postwar period saw a temporary withdrawal of German activity and an American interest in stress relaxation measurements with a biconical stress relaxation instrument being made semi-commercial by B. F. Goodrich in the 1970s. B. F. Goodrich has continued to improve this instrument over the past generation. The post-1975 period has also seen increased activity in Germany; Bayer AG(i) redesigned the Defo instrument and had it commercialized by Haake and (ii) devised a Mooney post-shearing stress relaxation measurement which has been commercially developed by Monsanto. A pressure-controlled rotational rheometer has been developed by Avon Rubber which allows for better study and characterization of slip. The development of instruments has been coupled with growing knowledge of the rheological properties of gum elastomers and carbon black compounds.
Practical Chemical Blowing Agents for Expanding Rubber
Authors: Rowland Donald G. 
Published: February 2011

Abstract
The most effective chemical blowing agents for producing cellular rubber products are ADCA, activated forms of ADCA, OBSH and DNPT. Blends of ADCA types and OBSH are also used quite extensively. These blowing agents may be used to make automotive weatherstripping, various types of athletic padding, insulation and flotation materials as well as numerous other expanded products.
The Effect of Zinc Distribution on the Mechanical Stability of NR Latex Concentrates
Authors: Davies R. T. , Pendle T. D. 
Published: February 2011

Abstract
Dithiothreitol (DTT) has been found to increase the mechanical stability of natural rubber (NR) latex concentrates, particularly in the case of low ammonia TZ (LATZ) latices. The DTT interacts with the zinc on the rubber particle surface to form an insoluble phase which then precipitates in the sediment phase of the latex. Zinc ions tend to destabilize latex by neutralizing some of the fatty acid anions and proteinate anions on the rubber particle surface and DTT increases the stability of latex by removing a large proportion of these zinc ions. The metal complexing agent EDTA is even more effective than DTT at increasing the mechanical stability of LATZ latex. EDTA removes all the zinc from the particle surface and also solubilizes zinc in the sediment, possibly liberating fatty acid anions from the sediment which could then stabilize the latex further. This effect may be useful because it provides a means of increasing or maintaining the stability of LATZ latex when addition of a surfactant is undesirable EDTA also improves the storage stability of a typical post-vulcanizable latex mix which contains zinc—added in the form of zinc oxide—and an accelerator.
The Efficiency of Peroxides for Curing Silicone Elastomers
Authors: Class J. B. , Grasso R. P. 
Published: February 2011

Abstract
Peroxides are preferred for heat curing vinylmethylsilicone (VMQ) elastomers because the free-radical-initiated crosslink does not reduce the inherent stability of the polymer. The objectives of this work were (1) to obtain information on the relationship between peroxide concentration and the physical properties of heat-cured silicone elastomers, and (2) to explain the suspected difference in efficiency of two peroxides, α,α′-di(tert-butylperoxy)-m/p-diisopropylbenzene (DBPIB) and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPH). VMQ bases and gums were cured with DBPIB and DBPH over a range of peroxide concentrations. Higher tensile modulus and higher delta torque (oscillating disk rheometer data) were observed when curing with DBPIB over the entire concentration range. This indicates that DBPIB produces a higher crosslink density than DBPH at equivalent molar concentrations. A series of calculations were performed, using computational chemistry techniques, to gain insight into the reason for the observed difference in crosslinking efficiency between DBPIB and DBPH. These calculations show that DBPIB is not more efficient than DBPH in abstracting hydrogen from the methyl groups of sihcone elastomers. The predominant cause for the difference in efficiency is related to the stability of the DBPH free radical. This radical is formed from hydrogen abstraction at the central ethylene moiety of DBPH by neighboring peroxy fragments. Therefore, DBPH is more susceptible to hydrogen abstraction, which consumes radicals in nonproductive (noncrosslinking) pathways This difference in peroxide efficiency may apply to other polymers.
2-(Isopropylsulfinyl)-Benzothiazole as a Delayed Action Thiazole Accelerator
Authors: Hopper Roger J. 
Published: February 2011

Abstract
At vulcanization temperatures, 2-(isopropylsulfinyl)-benzothiazole(ISB) generates 2-benzothiazole sulfenic acid as a reactive intermediate. In this respect (i.e., formation of a sulfenyl species), ISB is analogous to a benzothiazole sulfenamide, but without the built-in amine activation. Thus, ISB alone is slow, but responds to a variety of activators. The potential to independently select the activator can offer a wider latitude in meeting today's compounding challenges. For example, ISB activated by tetrabenzylthiuram disulfide represents a system devoid of precursors of volatile introsamines ISB with thiophosphoryl sulfides can provide effective, amine-free cure packages. Where nitrosamines are not a factor, tetramethylthiuram monosulfide (TMTM) remains the best general purpose activator. Examples of the effects of ISB/activator systems on cure characteristics and physical properties in a variety of recipes are presented. A unique, practical synthesis of ISB in two steps from MBT, propylene and bleach is outlined, and a more generally adaptable laboratory procedure is described in detail. Diagnostic reactions of ISB and substituent effects of related derivatives, designed to support the postulated acceleration mechanism, are described.