Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. III. The Effects of Certain Additives

1971 ◽  
Vol 44 (1) ◽  
pp. 29-39 ◽  
Author(s):  
V. L. Folt
Keyword(s):  
Natural Rubber ◽  
Room Temperature ◽  
Crystallization Process ◽  
Solidification Process ◽  
Polymer Chains ◽  
Capillary Rheometer ◽  
Subsequent Aging ◽  
Oil Blends ◽  
Flow Units ◽  
Static Conditions

Abstract Cis-polyisoprenes are readily crystallized under the pressure and orientation forces existing in a capillary rheometer. Oil-extension retards the rheometer crystallization process. However, natural rubber/oil blends containing up to 50 phr of oil are readily crystallized above room temperature. The retardation effect of oil-extension is not nearly as drastic as that produced by slight alterations in the stereoregularity of the polymer chains. ISAF carbon black significantly enhances the ease at which solidification of the melt can be effected in the capillary. Aging the black/rubber mix at room temperature enhances the ease of solidification. Shearing the aged black/rubber mix results in a retardation of the solidification process but subsequent aging of the sheared mix again enhances the ease of solidification in the capillary. Acetone extracted natural rubber crystallizes more easily in the capillary rheometer than the non-extracted material; a behavior in marked contrast to that observed under static conditions at −20° C where removal of the acetone solubles from natural rubber retards the crystallization process. A brief discussion of the crystallization mechanism in terms of supermolecular flow units is presented.

Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. II. The Effects of Experimental Parameters and Molecular Structure

1971 ◽  
Vol 44 (1) ◽  
pp. 12-28 ◽  
Author(s):  
V. L. Folt
Keyword(s):  
Molecular Structure ◽  
Molecular Weight ◽  
Natural Rubber ◽  
Crystallization Process ◽  
Complex Function ◽  
Capillary Rheometer ◽  
Optimum Conditions ◽  
Experimental Parameters ◽  
Static Conditions

Abstract Cis-polyisoprenes are readily crystallized under the pressure and orientation forces existing in a capillary rheometer. The ease at which crystallization can be effected is a complex function of the interrelationships existing among the temperature, the molecular weight, stereoregularity, and the dimensions of the capillary. For a given cis-polyisoprene and capillary, crystallization occurs more readily as the molecular weight is increased. Decreasing the diameter of the capillary and/or increasing the length of the capillary enhances the ease at which a given cis-polyisoprene can be crystallized. Using the optimum conditions presently available, natural rubber has been crystallized at 146° C. The ease at which crystallization is effected decreases drastically as the cis-1,4 content of the polyisoprene is reduced. Trans-1,4 and 3,4 are similarly effective in retarding the crystallization process and their effects are proportional to their concentrations in the molecular chains. However, polyisoprenes which will not crystallize under static conditions at −20° C are readily crystallized in the capillary rheometer at much higher temperatures.

Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. I

1971 ◽  
Vol 44 (1) ◽  
pp. 1-11 ◽  
Author(s):  
V. L. Folt ◽  
R. W. Smith ◽  
C. E. Wilkes
Keyword(s):  
Natural Rubber ◽  
Atmospheric Pressure ◽  
Room Temperature ◽  
Fibrillar Structure ◽  
Capillary Rheometer ◽  
X Ray ◽  
Complex Morphology ◽  
Structure Changes ◽  
Degree Of Orientation ◽  
Commercial Processing

Abstract Natural rubber is readily crystallized under the pressure and orientation forces existing in a capillary rheometer. The crystallization of natural rubber is readily effected over the temperature range covering commercial processing and fabricating temperatures. The crystalline rubber is stable at atmospheric pressure and room temperature. The observed crystalline melting point increases with increasing crystallization temperatures. Wide angle x-ray pictures show the crystals to be highly oriented in the direction of flow. Electron micrographs of fracture surfaces of the crystalline rubber show the existence of a very complex morphology. Where the degree of orientation is highest, a fibrillar structure is observed parallel to the direction of flow. The fibrillar structure changes to a shish-kebab structure about midway down the capillary. Apparently, a regrouping occurs with chain folded lamellae forming at right angles to the oriented fibrillar type crystals. A rotation of the chain-folded lamellae may occur as the exit end of the capillary is approached.

Color and Antioxidant Changes in Various Natural Rubber Processes

2015 ◽  
Vol 754-755 ◽  
pp. 230-234 ◽  
Author(s):  
Suwimon Siriwong ◽  
Adisai Rungvichaniwat ◽  
Pairote Klinpituksa ◽  
Khalid Hamid Musa ◽  
Aminah Abdullah
Keyword(s):  
Acetic Acid ◽  
Natural Rubber ◽  
Retention Index ◽  
Total Phenolic Content ◽  
Room Temperature ◽  
Phenolic Content ◽  
Total Phenolic ◽  
Lovibond Colorimeter

Fresh field natural rubber was coagulated by acetic acid, soaked in water at room temperature (WRT) or 70°C (W70) for 1 hr, and then dried in an oven at 40°C. Non-soaked natural rubber samples (NoW) served as a control. Two grades of natural rubber, namely air-dry sheet (ADS) and ribbed smoked sheet No.3 (RSS3) derived from the same latex, were also investigated. All dry rubber samples were characterized with Lovibond colorimeter according to ASTM D3157, as well as with a HunterLab spectrophotometer. Furthermore, all the dry rubber samples were dissolved in a chloroform:methanol mixture (4:1 v:v). The rubber was then precipitated out of the solution with methanol, and the remaining solution was quantitatively analyzed for total phenolic content (TPC). The plasticity retention index (PRI) was determined for all the dried rubber samples according to ASTM D3194. It was found that WRT, W70 and ADS were similar in lightness L*, while RSS3 had the lowest L*. W70 had the lowest redness a*, which increased in the order WRT, NoW, RSS3 and ADS. W70 also had the lowest yellowness b*, which increased in the order RSS3, NoW and WRT and ADS. Moreover, TPC was the lowest for the W70 sample, increasing in the order ADS, WRT, NoW and RSS3. The PRI was highest for W70, and decreased in the order WRT, RSS3, NoW and ADS. All of the PRI values observed were comparatively high relative to blocked standard Thai rubber 20 (STR20).

Graft Polymers Derived from Natural Rubber

1956 ◽  
Vol 29 (1) ◽  
pp. 99-105 ◽  
Author(s):  
G. F. Bloomfield ◽  
F. M. Merrett ◽  
F. J. Popham ◽  
P. Mc L. Swift
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Methyl Methacrylate ◽  
Transfer Reaction ◽  
Polymer Chains ◽  
Vinyl Monomers ◽  
Grafted Polymer ◽  
Polymeric Chains ◽  
Graft Polymers ◽  
Direct Growth

Abstract Graft polymers result when vinyl monomers are polymerized in the presence of natural rubber, either in solution or as latex, and some of the polymeric chains become attached to the rubber molecules. The properties of the natural rubber can be widely modified according to the nature and the amount of the grafted polymer. The polymer-modified natural rubber appears to be produced by direct growth of polymer chains on to rubber molecules rather than by a transfer reaction involving the rubber. Graft polymers of styrene and methyl methacrylate with natural rubber can be compounded and cured to give light-colored articles of good tensile strength, and rubber-methyl methacrylate graft polymers have outstanding flex-cracking and fatigue resistance.

scholarly journals Thermomechanical analysis of Natural Rubber behaviour stressed at room temperature.

2010 ◽  
Vol 6 ◽  
pp. 25008
Author(s):  
R. Caborgan ◽  
J.M. Muracciole ◽  
B. Wattrisse ◽  
A. Chrysochoos
Keyword(s):  
Natural Rubber ◽  
Room Temperature ◽  
Thermomechanical Analysis

Low Temperature Expansion of Polysulfide Rubbers

1966 ◽  
Vol 39 (2) ◽  
pp. 211-216
Author(s):  
B. A. Hunter ◽  
M. J. Kleinfeld
Keyword(s):  
Room Temperature ◽  
Liquid Mixture ◽  
Cumene Hydroperoxide ◽  
Polymer Chains ◽  
Nitrogen Gas ◽  
Blowing Agents ◽  
Disulfide Linkages ◽  
Novel Method ◽  
Rubber Product ◽  
Liquid Polysulfide Rubbers

Abstract A novel method for producing a cellular cured rubber product at room temperature has been developed. Pourable liquid polysulfide polymers are treated with a conventional oxidizing curative and selected water-sensitive or oxidation-sensitive blowing agents. Standing at ambient temperature the viscous liquid mixture gradually “rises” and cures to form a finely porous cellular rubber product. Conventional curatives employed include oxidizing agents such as lead peroxide and cumene hydroperoxide. These convert terminal or pendant thiol groups in the polysulfide polymer chains to chain-connecting disulfide linkages. Water is a byproduct of the curing reaction. In the presence of water-sensitive blowing agents such as, (1) metal salts of azodicarboxylic acid or, (2) metal hydride compounds the water produced in the cure reacts to form copious amounts of nitrogen or of hydrogen. Alternatively, oxidation-sensitive blowing agents such as p, p′-oxybis-(benzene sulfonyl hydrazide) react directly with the oxidizing curative to form nitrogen gas. The blowing reactions are concurrent with cure and efficient and controllable expansion can be achieved. The unique process offers possible economies and special properties in applications of liquid polysulfide rubbers as potting compounds, joint sealants, solvent resistant forms, and cold casting compounds.

scholarly journals Application of Ultrasonic or Microwave Radiation to Delay Crystallization and Liquefy Solid Honey

2021 ◽  
Vol 65 (2) ◽  
pp. 243-253
Author(s):  
Ewelina Sidor ◽  
Monika Tomczyk ◽  
Małgorzata Dżugan
Keyword(s):  
Microwave Radiation ◽  
Physicochemical Parameters ◽  
Room Temperature ◽  
Crystallization Process ◽  
Total Phenolics ◽  
Antioxidant Properties ◽  
Natural Process ◽  
Dpph Method ◽  
Phenolics Content ◽  
And Control

Abstract Crystallization of honey is a natural process occurring during honey storage and forces beekeepers to practice the decrystallization process, which mainly concerns honey heating. The aim of this study was to examine the possible use of ultrasounds or microwave radiation to delay the crystallization of honey and to liquefy crystallized honeys while maintaining their biological activity. Lime, acacia and multifloral honeys obtained from a local apiary were used. Fresh honeys were pretreated through ultrasounds (40 kHz, for 5 and 20 min) or microwaves (800 W, 4 x 30s) in order to obtain samples U5, U20 and M, respectively. Experimental and control samples were stored for twelve months at room temperature (20±2°C) without light. Crystallized honey was liquefied through the same methods of ultrasounds (sample U5* and U20*) and microwaves (sample M*). Naturally crystallized honeys were used as the controls. For fixed (U5, U20 and M) and decrystallized (U5*, U20*, M*) honeys, the water content (refractometrically), antioxidant properties (DPPH method), total phenolics content (Folin-Ciocalteu method) and enzymatic activity (diastase, α-glucosidase, β-galactosidase and α-mannosidase) were determined. The analyzed physicochemical parameters for both fixed and liquefied honeys did not differ significantly (P>0.05) in comparison to the control honey. Moreover, the decrystallization process increased the antioxidant activity of all tested honeys. The smallest changes in honey properties to ultrasonic treatments were observed, and this method was recommended to delay the crystallization process and significantly accelerate the liquefaction time of solid honeys without compromising its quality.

The Crystallization of a-ZnTe

1975 ◽  
Vol 53 (22) ◽  
pp. 2481-2484 ◽  
Author(s):  
J. B. Webb ◽  
D. E. Brodie
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Crystallization Process ◽  
Amorphous Material ◽  
Amorphous State ◽  
Zinc Telluride ◽  
Thermally Activated ◽  
Maximum Time

The crystallization of amorphous zinc telluride (a-ZnTe) has been studied as a function of temperature in the range 350 K < T < 390 K. The crystallization process is thermally activated with an activation energy of 1.6 eV. The time for the onset of significant crystallization at room temperature for films of air-annealed a-ZnTe is found to be ~100 years. The study of the crystallization process is essential in order to determine the maximum time allowed for a measurement to be performed at a given temperature on a sample of amorphous material without significantly altering its amorphous state.

Nanopores and nanosheets of α-Fe2O3 synthetized by electrochemical anodization and analysed by Raman spectroscopy

MRS Advances ◽  
2019 ◽  
Vol 4 (53) ◽  
pp. 2863-2871
Author(s):  
L.M.C. Pérez-Pérez ◽  
A. Báez-Rodríguez ◽  
L. García-González ◽  
J. Hernández-Torres ◽  
O. Velázquez-Camilo ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Crystalline Structure ◽  
Room Temperature ◽  
Ammonium Fluoride ◽  
Deionized Water ◽  
Electrochemical Anodization ◽  
Vibration Modes ◽  
Spectroscopy Technique ◽  
Temperature Scanning ◽  
Static Conditions

Abstract:Nanoparticles and nanopores of iron oxide were synthesized by electrochemical anodization, in an electrolytic medium of ammonium fluoride (NH4F), deionized water and ethylene glycol. After anodization, the Fe foils were annealed at 450 °C for 2 hours. Different anodization times and two concentrations of NH4F (0.1 M and 1.2 M) were evaluated, under static conditions at room temperature. Scanning Electron Microscopy showed nanopores (0.1 M) and nanoparticles (1.2 M). Eight vibration modes characteristic of α-Fe2O3 were found with Raman spectroscopy technique. Relationship between the modes Eu(LO) and 2Eu(LO) was found, therefore, their association with the disorder in the crystalline structure can be determined and it was also found that 2Eu(LO) intensity mode at a concentration of 1.2 M is larger than 0.1 M nanostructures, the FWHM of the A1g mode at 227 cm-1 corresponding to the Fe3+ ions and the Eg at 293 cm-1 mode caused by the O2- ions was also analyzed and founded that the crystalline structure of hematite can be determined by the A1g mode at 227 cm-1.

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