How can properties of rubber be changed

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Latest News Want to read the latest news from Monroe Engineering? BLOOM — A change in the surface appearance of a product caused by the migration of a solid or liquid material to the surface due to incompatibility. BLOW — The volume expansion during the forming of sponge rubber expressed either in percent or a ratio. BOND — The union of materials by use of adhesives, usually used in relation to parts vulcanized after attaching. BOOT — A bellows type covering to exclude dust, dirt, moisture, etc.

BUMPING — A procedure in molding rubber parts where pressure to the press ram is alternately applied and released to aid in the venting of trapped air and gases from the mold. Derived from butanes or as by-product in production of ethylene. It is the major constituent in copolymers with styrene and acrylonitrile and is polymerized by itself to form polybutadiene.

Butyl rubber is the common name for such materials. CALENDER — A precision machine equipped with three or more heavy, internally heated or cooled rolls, revolving in opposite directions, which is used for the highly accurate continuous sheeting or plying up of rubber compounds, and fractioning or coating of fabric with rubber compounds.

It may be produced by several processes, each imparting different properties to the carbon black, These are channel black, furnace black and thermal black. It may be produced by mill or Banbury mixing the black into the rubber or adding the black to a synthetic rubber latex such as SBR followed by coagulation, washing and drying of the mixture.

CAST — To form a part by filling a mold cavity with a liquid resin or rubber and then curing to a solid at room temperature or with heat, but generally without pressure. Molds may be single or multi-cavity.

CELL — A single, small open space surrounded partially or completely by walls as in sponge. COLD BEND — A test in which a sample of wire or cable is wound around a mandrel of a specified size within a cold chamber, at a specified temperature for a given number of turns at a given rate of speed. The sample is removed and examined for defects or deterioration in the materials of construction. COMPOSITE — A homogeneous material created by the synthetic assembly of two or more materials a selected filler or reinforcing elements and compatible matrix binder to obtain specific characteristics and properties.

Sometimes called stock. Generally obtained after stress was applied for a given length of time at a specified temperature. Or also by passing through a liquid salt or bead bath at C F at atmospheric pressure. CREEP — The deformation in either vulcanized or unvulcanized rubber under stress that occurs with lapse of time after the immediate deformation. Once cross linked, materials cannot be reprocessed.

A form of curing. Degree of crystallinity effects stiffness, hardness, low temperature flexibility and heat resistance. CURE — Similar to cross linking and vulcanization, except that vulcanization refers specifically to sulfur cross linking, while cure covers all types sulfur, peroxide, radiation, etc. It measures the rate of formation of cracks in a standard molded test bar.

High values indicate harder materials. The value may be taken immediately, highest point or after a very short specified time. EPDM — ASTM abbreviation for a terpolymer of ethylene, propylene, and a diene with the residual unsaturated portion of the diene in the side chain. EBONITE — A term for hard rubber, made by vulcanization of rubber with high levels greater than 30 parts of sulfur, where the high hardness is due to the action of the sulfur.

This generally refers to a synthetic polymer as opposed to rubber which preferably indicates the natural products. FADE-O-METER — An apparatus for accelerated light aging and light fastness testing of sample of vulcanized rubber and plastic specimens under the action of artificial light from an electric arc between two carbons. FILLER — A solid compounding material which may be added, usually in finely divided form, in relatively large proportions, to a polymer.

Generally to reduce cost or modify properties. Mold overflow. Also called recipe. GR-S — Obsolete description of styrene-butadiene rubber. GAGE — Refers to a dimension, generally thickness of a product, as measured by a gage of some type.

Named after its inventor, Benjamin Garvey. GRAIN — The unidirectional orientation of rubber or filler particles occurring during processing extrusion, milling, calendering resulting in anisotropy of a rubber vulcanizate.

It is soft and highly resinous. There is currently little commercial use. It contains no filler, reinforcing agents or plasticizers. It differs in that it is highly transpolyisoprene like balata as compared to natural Hevea rubber which is cis-polyisoprene.

Its commercial usage is generally limited to underwater cable. HEAT AGING — When specimens of vulcanized rubber are given accelerated aging in air or oxygen at elevate temperatures and in some cases, pressure for specified periods of time. The deterioration is generally noted as a percent change from originally measured properties.

Characteristics of diene containing polymers. Since vulcanization takes place at elevated temperatures, incipient cure or scorch can take place if heat history has been excessive. Aliphatic hydrocarbons are straight chain compounds and aromatic hydrocarbons are based on the cyclic or benzene ring. They may be gaseous, methane, ethylene, butadiene liquid hexane, benzene or solid natural rubber, naphthalene, cis-polybutadiene.

It is the difference between the energy of the deforming stress and the energy of the recovery cycle. INERT — A material that has little tendency to reinforce or have any other effect upon the properties of vulcanizates.

The extruder may be screw or plunger type. The mixing chamber is jacketed and may be heated or cooled, as may be the rotor. It consists of a notched specimen supported as a cantilever which is struck by a pendulum blow. Also called poor knitting. KNOTS — Lumps which appear in a stretched rubber part, generally due to poor dispersion of a curative, such as sulfur. LIM — Liquid injection molding. A molding process in which one or more liquid materials are injected into a mold held at room or elevated temperatures catalysed to cure in a very short period of time.

RIM, reaction injection molding, is a special case referring to catalyzed liquid urethanes reacting in the mold at room temperature. It refers to the emulsion obtained from the tree or plant or produced by emulsion polymerization. The lead covering acts as a mold during vulcanization. It is designed to evaluate the crystallizing tendency of cured compounds at low temperatures. The specimen is elongated, frozen to an inelastic state, and released while allowing the temperature to rise at a uniform rate.

The length of the specimen is measured at regular temperature intervals while it is retracting. External sprayed on to reduce tendency to stick to a mold. MANDREL — A hollow or solid metal pole used as a form for producing lengths of tubing, hose, or for tubes later cut on a lathe into gaskets. School glue, which is a solution of polyvinyl acetate PVA , can be cross-linked by the borate ion, BO contained in Borax laundry detergent. There are many variations to this demonstration that can be utilized to obtain different consistencies of the product slime vs.

Students should be broken into groups of and each group should be given a plastic cup, a plastic spoon, roughly 50 mL of school glue, and roughly 20 mL of a prepared borax solution made by combining roughly 1 g of Twenty Mule Team Borax laundry detergent to roughly 25 mL of water. Students should add the glue to an empty plastic cup and stir the glue with a plastic spoon, making observations about the properties of the glue.

Students should then add about 20 mL of the prepared Borax solution and stir, making observations of any changes to the properties of the glue. After allowing the students to manipulate their newly cross-linked polymer, students should be allowed time to hypothesize what may have occurred with the addition of the Borax solution. The concept of cross-linking can be introduced as the explanation.

Cross-linking polymers is an important process in manufacturing and is a great example of how these macromolecules can be manipulated to meet commercial needs, such as with tire production. Other than the observed differences in properties, polymer scientists are also interested in how to determine the degree of cross-linking that has occurred cross-link density. There are several ways to test the presence of cross-links using expensive and unavailable equipment, but the simplest method to determine not only if cross-linking has occurred, but also the density of these cross-links, is a process called a swelling test.

Samples of the cross-linked rubber are submerged in an organic solvent for a specified amount of time determined by the type of rubber in the sample.

If there is no cross-linkage between the rubber chains as with rubber cement , the polymer chains should begin to dissolve into the solvent and, thus, the sample should decrease in mass over time. The organic solvents typically used in a lab setting hexane, toluene, chloroform, etc. It is important to remind the students why mineral oil will be used as the solvent rather than just water polymers are generally nonpolar, therefore a nonpolar solvent will be necessary to interact with the rubber samples.

The instructor should introduce swell testing and inform students that it is an excellent way for a scientist to determine whether or not a sample of rubber has been cross-linked.

To increase the level of critical thought and application of the concept, the students should not be told what results to expect, but be allowed to predict the results and later hypothesize the explanation for their results themselves. To do this, a layer of the latex can be poured onto any surface baking tray, plate, sheet of aluminum foil, etc.

Spread the latex evenly so that a relatively consistent thickness is obtained. The latex should be allowed to stand at room temperature for days to cure. The rubber cement can be dried in a similar way, however it is advised to pour the layer of rubber cement onto a sheet of aluminum foil, as it may be slightly difficult to remove all of the sample after it has dried.

Groups of students should obtain a roughly 1 g sample of both types of rubber. The samples may be provided by the teacher or be obtained by students by cutting a single piece from the larger sample using scissors. It is not necessary that the samples be exactly 1 g, but the students should record the exact mass of their sample before beginning the test. Students should make and record observations of the samples and note any similarities or differences between each type of rubber.

Once the masses of both samples have been recorded and observations have been made, the samples should be placed in separate clean glass containers that can be covered. The containers should be able to hold at least 60 mL of liquid.