What is rubber

In this book the word rubber means uncrosslinked raw material unless stated otherwise. By posing the question what is rubber we are concerned with fundamental but very common sense meaning of the term. 

The word, rubber usually indicates such substances as NR, SBR and so on. But, this does not lead to the definition of rubber. The definition is actually based on a very simple experience  

The substances nsnally called rnbber, exhibit the above behaviour at ambient conditions. However, the same snbstance called rubber loses the behaviour (i) at low temperatures, becoming a glass. When a rnbber is heated to a high temperature, it becomes a viscous fluid, losing the behavionr described in (ii). 

Here the word, rnbber, is nsed in two different ways one is referring to specific substances snch as natnral rnbber and SBR. The other is an expression of mechanical behaviour for 

In the rest of the book the former will be termed as gum rubber and the latter as the 

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A Methyl vinyl ketone, CH3CCH=CH2, can be polymerized by addition polymerization. The addition reaction involves only the C = C bond. Write the structural formula of a four-unit segment of this polymer. A (a) What is rubber (b) What is vulcanization (c) What is the purpose of vulcanizing rubber (d) What are fillers and reinforcing agents (e) What is their purpose ... 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

Rubber used in practical applications is crosslinked through disulfide (-S-S-) bonds, and is known as vulcanized rubber. Can you name another important class of polymers which are crosslinked through disulfide bonds Examine vulcanized rubber. How many individual strands does it comprise Are these strands of natural rubber or of gutta-percha What is the percentage (by weight) of sulfur incorporated into the polymer (The molecular weight of the sample is 1701 amu.) Does this classify as a low-sulfur polymer (<3%), a high-sulfur polymer (>10%) or in between ... 

As SR decreases, 1 must be decreased too (and thereby also the inlet pressure loss/total pressure ratio is decreased). This is what is really observed when dispersed fillers are added to polymer [182,190,193,194], The rubber phase in heat resistant polystyrene behaves much like a dispersed filler it also diminishes the inlet correction [195]. For polystyrene with different fillers the following relationship was found to be valid [196] ... 

RAPRA free Internet search engine. The number of plastic-related web sites is increasing exponentially, yet searching for relevant information is often laborious and costly. During 1999 RAPRA Technology Ltd., the UK-based plastics and rubber consultancy, launched what is believed to be the first free Internet search engine focused exclusively in the plastics industry. It is called Polymer Search on the Internet (PSI). It is accessible at www.polymersearch.com. Companies involved in any plastic-related activity are invited to submit their web-site address for free inclusion on PSI. RAPRA Technology s USA office is in Charlotte, NC (tel. 704-571-4005). 

Since the initial disclosure by Allcock, workers have sought to answer various questions 1) What is the nature of the polymerization process (mechanism) 2) What is the structure of poly(dichlorophosphazene) that distinguishes it from the insoluble "inorganic rubber (III) 3) The substitution process gives a seemingly endless variety of products. What are the limitations or... 

What is meant by the statement plastics and rubbers comprise a statistical distribution of molecular lengths ... 

What is the difference between a rubber and a plastic Why are they both polymers ... 

A substance which prevents the participation of a metal or its compounds in a chemical reaction. The catalytic effect of heavy metals, mainly copper and mangagese, on the oxidation of unsaturated compounds (e.g., rubber) results in very poor ageing. If the metal can be converted into what is known as a chelate co-ordination compound, by the use of a sequestering agent, ageing is considerably improved. See Chelating Agent. 

Water in the gaseous state it is a convenient source of heat widely used in the curing of rubber products. See Open-Steam Curing, Press Curing. Steam is really a colourless gas and what is usually termed steam (issuing from an autoclave, a press, thermometer bleed pipe, etc.) is really droplets of water which result from the steam meeting the cooler air of the atmosphere. Steam Trap... 

CP-1 was assembled in an approximately spherical shape with the purest graphite in the center. About 6 tons of uranium metal fuel was used, in addition to approximately 40.5 tons of uranium oxide fuel. The lowest point of the reactor rested on the floor and the periphery was supported on a wooden structure. The whole pile was surrounded by a tent of rubberized balloon fabric so that neutron absorbing air could be evacuated. About 75 layers of 10.48-cm (4.125-in.) graphite bricks would have been required to complete the 790-cm diameter sphere. However, criticality was achieved at layer 56 without the need to evacuate the air, and assembly was discontinued at layer 57. The core then had an ellipsoidal cross section, with a polar radius of 209 cm and an equatorial radius of309 cm [20], CP-1 was operated at low power (0.5 W) for several days. Fortuitously, it was found that the nuclear chain reaction could be controlled with cadmium strips which were inserted into the reactor to absorb neutrons and hence reduce the value of k to considerably less than 1. The pile was then disassembled and rebuilt at what is now the site of Argonne National Laboratory, U.S.A, with a concrete biological shield. Designated CP-2, the pile eventually reached a power level of 100 kW [22],... 

The best known aspect, and the first one to find commercialization in the direct fluorination area, was the fluorination of polymer surfaces. This Lagow-Margrave invention, trademarked Fluorokote, involved many types of polymeric materials in various forms e.g., polyethylene bottles, polypropylene objects, and rubber gloves. Polyethylene bottles are easily given fluorocarbon surfaces (>0.1 mm), and this has been commercialized. Air Products has at least 20 licenses for what is known as their Aeropak process and Union Carbide has a Linde Fluorination process as well. Applications in chemical, pharmaceutical, and cosmetic storage are widespread. 

Hydrophobicity loss and recovery in silicone rubbers has been extensively studied and reviewed in a few recent publications with numerous references.581,582 The ability to recover hydrophobicity after oxidation or contamination is considered as one of the important features determining the applicability of silicones in electrical and other outdoor insulation. The methods of studying of what is known as aging and recovery mechanisms are discussed. 

What is the composition of the first copolymer butyl rubber chains produced form equimolar quantities of the two monomers ... 

What is the most important contribution to retractile forces in highly elongated rubber ... 

What is present in so-called vulcanized rubber compounds ... 

Preparation of Chromium(II) Chloride. (Perform one of the following two experiments.) 1. Put several pieces of metallic chromium into a test tube, pour in 2-3 ml of a 20% hydrochloric acid solution, and insert a stopper with a gas-discharge tube. Connect to the latter a rubber tube with a slot closed by a glass rod (a Bunsen valve. Fig. 125). What is the role of the slot in the rubber tube Identify the substance in the solution. Write the equation of the reaction. 

Natural rubber is a polymer of isoprene- most often cis-l,4-polyiso-prene - with a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins and inorganic materials is found in natural rubber. Polyisoprene is also created synthetically, producing what is sometimes referred to as "synthetic natural rubber". Owing to the presence of a double bond in each and every repeat unit, natural rubber is sensitive to ozone cracking. Some natural rubber sources called gutta percha are composed of trans-1,4-poly isoprene, a structural isomer which has similar, but not identical properties. Natural rubber is an elastomer and a thermoplastic. However, it should be noted that as the rubber is vulcanized it will turn into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both, i.e., if it is heated and cooled, it is degraded but not destroyed. 

What is certain is that the initiation and propagation of a tear is a real and very important factor in the failure of rubber products, being involved in fatigue and abrasion processes as well as the catastrophic growth of a cut on the application of a stress. There is, therefore, considerable interest in the tearing resistance of rubbers. What is uncertain is how tear resistance should be measured and the results interpreted. 

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