The Creaming of Hevea Latex by Colloids

1938 ◽  
Vol 11 (4) ◽  
pp. 608-623
Author(s):  
C. F. Vester
Keyword(s):  
Negative Charge ◽  
Dispersed Phase ◽  
Rubber Content ◽  
Rubber Latex ◽  
Ionogenic Groups ◽  
Rubber Particles ◽  
Dispersing Medium ◽  
Almost All ◽  
Short Time ◽  
Serum Components

Abstract Hevea latex is generally considered to be a suspension of rubber particles of various dimensions up to about 3 µ. The rubber hydrocarbon contains no “ionogenic groups,” and it is believed that part of the serum components imparts a negative charge to the rubber particles. Almost all latex imported into Europe is preserved by means of 0.5 to 0.7 per cent of ammonia. This ammonia plays a three-fold part: (1) it prevents premature souring of the latex; (2) it increases somewhat the charge on the particles; and (3) it attacks all types of serum components so that within a short time the “preserved” latex is hardly comparable with natural latex. As with all suspensions in which the dispersed phase is lighter than the dispersing medium, rubber latex exhibits the phenomena of creaming. The density of the rubber particles is approximately 0.914, that of the medium, 1.020. By means of creaming, it is possible to obtain a latex (1) which has a higher rubber content, whereby transportation space and cost are saved, and (2) which contains no components having a tendency to deposit a sediment. The natural creaming of latex, which is of no importance technically, was observed by Faraday as early as 1825.

The State of Polydispersion of Hevea Latex. I

1946 ◽  
Vol 19 (1) ◽  
pp. 176-186
Author(s):  
J. H. E. Hessels
Keyword(s):  
Protein Content ◽  
Hevea Brasiliensis ◽  
The State ◽  
Rubber Content ◽  
Rubber Latex ◽  
Latex Particles ◽  
Rubber Particles ◽  
The Subject ◽  
Points Of View ◽  
Good Agreement

Abstract The rubber particles in the latex of Hevea brasiliensis are present in the form of a polydispersion, and their diameters lie within the range of 0.1 to 3 microns. The rubber hydrocarbon itself is composed of a mixture of macromolecules of different degrees of polymerization. Rubber latex is, therefore, a system which is at the same time both polydispersed and polymolecular. It is well known that the degree of dispersion of a substance governs to a great extent certain properties of the substance. Moreover, astonishing as it may seem, in the great number of investigations which have been made of the composition and properties of latex and crude rubber, almost no attention has been paid to the part which may be played by the dimensions of the latex particles. However, in an investigation concerned with the centrifugation of latex, Loomis and Stump have called attention to this possibility, and in a study of latex obtained by fractionation, and in which the majority of the latex particles were of large dimensions, McGavack came to the conclusion that the protein content is proportional to the surface area of the globules. This limited knowledge of the subject seemed to warrant a more thorough study of the problem, which is of fundamental importance both from the theoretical and practical points of view. The investigation as a whole divided itself into three essential parts: (1) separation of latex into fractions containing particles of different sizes, and measurement of the state of dispersion in these fractions, (2) a study of the relation of these fractions to the composition of the rubber, i.e., the relation between the content of nonrubber components and the size of the latex particles, and (3) a study of the changes in the properties of the rubber hydrocarbon with change in the size of the latex particles. The latex used in this investigation was ordinary latex, containing 38–40 per cent dry-rubber content and preserved with ammonia. For the most important points, a concentrated latex (creamed latex containing 60 per cent dry-rubber content) was also tested. These two latices were about two years old when the investigation was started, and they gave results which were in good agreement with each other. In the present paper, only the data obtained with the first of the two latices are presented.

Some Properties of Rubber Latex

1938 ◽  
Vol 11 (3) ◽  
pp. 479-481
Author(s):  
Ernst Schmidt ◽  
Paul Stamberger
Keyword(s):  
Aqueous Phase ◽  
Electrophoretic Deposition ◽  
Distilled Water ◽  
Cent Solution ◽  
Rubber Latex ◽  
Rubber Particles ◽  
Serum Components

Abstract Rubber latex of the commercial type preserved by ammonia was freed almost completely of its serum components by a method involving two steps: 1. Electrophoretic deposition of the rubber particles on a membrane, followed by 2. Dispersion of the resultant paste in a 0.6-per cent solution of ammonia in distilled water. This process was repeated until the aqueous phase obtained from this separation was free of non-rubber components in the latex.

scholarly journals Return to Exercise After Covid-19: Which One is the Best Strategy?

2021 ◽  
Vol 61 (2) ◽  
pp. 122-132
Author(s):  
Murat Erdoğan ◽  
Sevgi Sökülmez-Yildirim ◽  
Nasuh Evrim Acar ◽  
Okan Kamiş
Keyword(s):  
Individual Performance ◽  
Physical Distance ◽  
Personal Hygiene ◽  
Moderate Intensity ◽  
New Techniques ◽  
Recreational Athletes ◽  
Special Places ◽  
Almost All ◽  
Short Time ◽  
New Strategies

Summary Coronavirus (Covid-19), which began in China as of 2019 and spread to almost all over the world in a short time; has shown that we need to plan our life with new strategies as well as changing our current lifestyle today. While we must implement new ways to prevent against Covid-19 and maintaining our healthy lives, we must also design new strategies for returning to sports and physical activities. Therefore, the purpose of this study was to reveal the return strategies for professional and recreational athletes during the quarantine periods in light of evidences. In this regard, firstly we examined the existing literature regarding return strategies to sports. As a result, individual performance and personal hygiene conditions should be considered, and athletic performance should be preserved while keeping a physical distance from teammates and others. The use of masks in sports should be encouraged, but new techniques should be developed by investigating the effect on performance. Consequently, for healthy individuals, low to moderate intensity (not high-intensity) exercise may be beneficial and recommend. However, due to the risk of spreading (person-to-person or contaminated surfaces), exercise is recommended in special places with good ventilation and the use of personal types of equipment.

Laboratory Evaluation of Rubberized Binder and Mix Containing a Low Content of Devulcanized Rubber Modifier

2020 ◽  
Vol 2674 (11) ◽  
pp. 53-63
Author(s):  
Yanlong Liang ◽  
David Jones ◽  
John T. Harvey ◽  
Jeffery Buscheck
Keyword(s):  
Asphalt Binder ◽  
Fatigue Cracking ◽  
Laboratory Evaluation ◽  
Rubber Content ◽  
Area Index ◽  
Lower Phase ◽  
Waste Tires ◽  
Stiffness Reduction ◽  
Rubber Particles ◽  
Devulcanized Rubber

This paper evaluates the mechanical properties of rubberized asphalt binder and mix containing 5% and 10% rubber. This rubberized asphalt binder was manufactured in a field-blend process using devulcanized rubber particles, finer than 250 microns, derived from waste tires. Comparison between the rubberized binder and the base binder test results showed that the rubberized binders had higher complex moduli and lower phase angles at the grade temperature. They also had a higher percentage recovery in the multiple stress creep recovery test, and a significant creep stiffness reduction in the bending beam rheometer test. Given the low rubber content and small rubber particle size, this rubberized binder can be used in dense-graded mixes, whereas asphalt rubber binders, with larger rubber particles and higher rubber content (>15%), must be used in gap- or open-graded mixes. This rubberized dense-graded mix met the volumetric design criteria at the same binder content as the control mix prepared with the unmodified base binder. Laboratory tests on the mix included repeated load triaxial, Hamburg wheel track, flexural dynamic modulus, and beam fatigue. The rubberized mixes had slightly lower stiffnesses than the control mix, but better resistance to moisture damage, rutting, and fatigue cracking. A strong linear correlation was found between the carbonyl area index and the rheological properties of the long-term aged binder and fatigue life of the mixes. Based on these findings, these rubber-modified binders can be considered for use in dense-graded mixes to improve overall performance and make use of waste tires.

Influence of Morphology on Mechanical Properties under the Combined Use of SEBS and EOr as Elastomer in PP/Elastomer/Filler Ternary Composites

2011 ◽  
Vol 19 (9) ◽  
pp. 725-732
Author(s):  
Shigeki Hikasa ◽  
Kazuya Nagata ◽  
Yoshinobu Nakamura
Keyword(s):  
Mechanical Properties ◽  
Impact Strength ◽  
Triblock Copolymer ◽  
Continuous Phase ◽  
Dispersed Phase ◽  
Impact Properties ◽  
Combined Use ◽  
Poly Ethylene ◽  
Almost All ◽  
The Impact

The influences of combined elastomers on impact properties and morphology of polypropylene (PP)/elastomer/CaCO3 ternary composites were investigated. In the case that polystyrene- block-poly(ethylene-butene)- block-polystyrene triblock copolymer (SEBS) and poly(ethylene- co-octene) (EOR) were used as elastomers, a sea-island structure consisting of EOR dispersed phase and SEBS continuous phase was formed. The elastomer and the CaCO3 particles were separately dispersed in PP matrix. In the case that carboxylated SEBS (C-SEBS) and EOR were used, the C-SEBS particles were dispersed in the EOR particles. Almost all of the CaCO3 particles were dispersed in the PP matrix, although some of the CaCO3 particles were dispersed in the C-SEBS/EOR combined particles. Impact strength improved with an increase of incorporated CaCO3 particles. The effect of elastomer on the impact strength was SEBS ≥ SEBS/EOR > EOR = C-SEBS/EOR > C-SEBS. The morphology formed by elastomer and CaCO3 particles strongly affected the impact properties of the ternary composites.

scholarly journals Effects of inclusion of granulated rubber tires on the mechanical behaviour of a compressive sand

2020 ◽  
Vol 57 (5) ◽  
pp. 763-769 ◽  
Author(s):  
W. Li ◽  
C.Y. Kwok ◽  
K. Senetakis
Keyword(s):  
Particle Size ◽  
Shear Strength ◽  
Mechanical Behaviour ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Rubber Content ◽  
Filling Materials ◽  
Rubber Particles ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

Drained triaxial shearing tests were performed on a well-graded compressive sand (completely decomposed granite, CDG) and its mixtures with granulated rubber tires to investigate the effects of rubber size and content on their mechanical behaviour. Three sizes of rubber particles, GR1, GR2, and GR3, were used with size ratios to CDG (D50,rubber : D50,CDG) of 0.9, 3.5, and 7.2, respectively, and the rubber content ranged from 0% to 30%. The results show that for CDG–GR1 mixtures, the strength decreases with increasing rubber content, while for CDG–GR2 and CDG–GR3 mixtures, the strength decreases only at 10% rubber content and then increases markedly with increasing rubber content. The increase of strength is mainly because the inclusion of large rubber particles widens the particle size distributions of the mixtures, resulting in denser packings. The denser packings also lead to a decrease in compressibility. At larger size ratio and higher rubber content, the CDG–rubber mixtures show higher shear strength and lower compressibility than pure CDG, which indicates the CDG–rubber mixtures are very suitable to be used as filling materials.

Improved Deproteinization Process for Protein-Free Natural Rubber Latex

2013 ◽  
Vol 844 ◽  
pp. 474-477 ◽  
Author(s):  
Wiwat Pichayakorn ◽  
Jirapornchai Suksaeree ◽  
Wirach Taweepreda
Keyword(s):  
Natural Rubber ◽  
Negative Charge ◽  
Ph Value ◽  
Natural Rubber Latex ◽  
Solid Content ◽  
Enzyme Treatment ◽  
Distilled Water ◽  
Rubber Latex ◽  
Total Solid Content ◽  
Leaching Process

Hev b1-14 type proteins in natural rubber latex (NRL) have been identified as allergens in immunogenic responses. Several methods have been developed to reduce these proteins from NRL such as enzyme treatment, centrifugation, creaming, simple or ultrasonic leaching, and chlorination. In this work, the improvement of deproteinization of NRL was developed using the combination of enzyme treatment and leaching processes. The fresh NRL was incubated with 0.2 phr proteolytic alcalase enzyme, and preserved with 2%v/v paraben concentrate in the presence of a 2%v/v sodium lauryl ether sulfate (SLES) as a surfactant at 37°C for 24 hours, and then centrifuged. The upper rubber mass was then leached for three times with either distilled water, a 1%v/v SLES solution, or a mixture of 1%v/v SLES and 2.5%v/v ethanol, and then finally re-dispersed in distilled water. It was found that the increasing process of leaching with either 1%v/v SLES or a mixture of 1%v/v SLES and 2.5%v/v ethanol had the higher efficacy to reduce the remained protein in deproteinized NRL (DNRL). The best deproteinized process was the enzyme treatment and followed by the three times leaching process with a mixture of 1%v/v SLES and 2.5%v/v ethanol, that could completely reduce the proteins in DNRL to 0%. This DNRL had the pH value, viscosity, dry rubber content, and total solid content of 7.41, 13.82 cps, 42.57%, and 44.63%, respectively. Its particle size was 626.23 nm with low polydispersity index of 0.16. The negative charge of SLES could increase the higher negative charge of DNRL to-63.20 mV that exhibited very good physical stability during storage. In conclusions, the combination of enzyme treatment and leaching process with both SLES and ethanol was successful to produce the protein-free DNRL. This DNRL could be further used for several applications including medical skin products.

Microturbidimeter for Determination of Rubber Content of Latex

1931 ◽  
Vol 4 (4) ◽  
pp. 601-611
Author(s):  
S. D. Gehman ◽  
J. S. Ward
Keyword(s):  
Particle Size ◽  
Rubber Content ◽  
Mean Particle Size ◽  
Rubber Particles ◽  
Color Filters

Abstract It is desirable to devise a method for determining the dry rubber content of latex which will be both more rapid than the two trial coagulation methods and more precise than the hydrometric method. The turbidity of latex, depending upon the volumetric number and size of the suspended rubber particles, offers a satisfactory criterion for the determination of the rubber content of latex. A microturbidimeter, herein described, has been adapted to such determinations. It permits more rapid determinations of the rubber content than the two trial coagulation methods. Its precision is less than the lengthy trial coagulation method, involving coagulation, creping, and drying, but is probably greater than that of the shortened trial coagulation method involving only coagulation and creping. Its precision is approximately 1 per cent rubber in 35 per cent latex. The turbidity of latex obeys the turbidity-dilution law for rubber-content values less than 15 per cent. The use of color filters, transmitting the shorter wave lengths of light, minimizes the effects of a difference in the effective mean particle size of different kinds of latex.

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