Part 11
Text 11
Thermoplastic elastomers
(continued)
Applications
The basic properties of the materials bring the advantages of both rubbers and the thermoplastics together in the same product and introduce the potential of manufacture rubber articles by the use of modern, high speed, automatic thermoplastics processing techniques from materials in the price range close to that of other general purpose rubbers . They are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided.
Like those of other polymers, their properties such as solution and bulk viscosities, hardness, tensile strength, et cetera, can be varied by suitable changes in molecular weight and monomer ratio. The materials can be modified to impart hardness and abrasion resistance, softness, flexibility, improve flow and other desirable properties without unduly affecting the strength of the polymer network, its thermal lability, or the capability of obtaining desirable melt flow characteristics.
These materials contain no gel. In crumb form, as Kraton 101 or Kraton 102, they readily dissolve in conventional rubber solvents; the premastication and cutting needed with baled rubbers is thus avoided. These materials give cast films with tensile strengths 4,500 - 5,000 psi, and can be formulated with conventional resins to produce excellent pressure sensitive, hot melt, and contact adhesives.
The products, which have so far been designed around these materials, range from soft, transparent rubbers to hard, highly abrasion resistant materials.
Summary
New styrene - butadiene copolymer without chemical vulcanization, exhibit true elastomeric properties, that is snappy return from high elongation, resilience, good tensile strength, and low set, together with rubbery frictional properties and melt flow characteristic similar to those of conventional thermoplastics. The unique properties of these polymers are derived from the complete reversibility of the interchain forces, which constitute crosslinks at ambient temperatures but are not operative in a melt or in a solution. Stress-train properties are essentially unaffected by repeated melting (or dissolution) and recovery of solid polymer.
These novel products permit the manufacture of elastomeric articles by the use of high -speed thermoplastics processing techniques. No curing step is used, hence, lengthy mixing processes are avoided. Scrap can be recycled.
Like conventional natural rubber or SBR vulcanizates, the thermoplastic elastomers retain elastomeric properties down to low temperatures (- 700F). In this, the behavior contrasts with conventional thermoplastics which lose flexibility at temperatures only slightly below ambient.
The polymers are soluble in conventional rubber solvents and are thus suitable for formulation of adhesives, sealants and coatings. The versatility of the materials is such that special properties, such as ozone resistance, can be introduced by the use of simple modifications.
Notes
1. general purpose rubbers: cao su ®a dông tæng hîp
2. in nib form: d¹ng ban ®Çu, nguyªn thuû
3. can be formulated: cã thÓ ®îc trén víi
Exercises
I. Answer the following questions:
1. What kinds of thermoplastic elastomers are known nowadays?
2. What is the nature of polymeric chains of thermoplastic elastomers?
3. How many monomers may be used to prepare thermoplastic elastomers?
4. What properties of thermoplastic elastomers are truly elastomeric?
5. What can you say about the behavior of thermoplastic elastomers at low temperatures?
6. What articles may one produce from thermoplastic elastomers?
7. Is it possible to recycle the scraps from the fabrication of elastomeric articles?
II . Translate the following sentences into Vietnamese, paying attention to the words in bold type:
1. Vulcanization is a vitally important part of all rubber processing.
2. To impart the materials hardness, softness and other desirable properties, the materials can be modified.
3. Rigid polymers displaced traditional materials partly because of the economic advantages.
4. A number of scientists took part in the research of new elastic materials to be applied in surgery.
5. The alkyl of R group parts company from the carbonyl carbon exists for a time as a free radical.
III. Translate the following sentences into Vietnamese paying attention to the words in bold type:
1. Thermoplastic elastomers are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided.
2. There are still some plastics, more or less rubbery, available in emulsion or dispersion form.
3. Vinyl chloride and vinyl copolymer latices are available both untreated and preplasticized.
4. There are now available several modified Buna n latices having rather distinctive properties.
5. Butadiene, which can be made from readily available acetylene, is one of the raw materials of synthetic rubber.
IV. Give Vietnamese equivalents to the following words:
Article
Formulation
Novel
processing
readily
resin
V. State to what parts of speech the following words belong, paying attention to the suffixes:
a)
Ambient
Conventional
Elastic
Elastomeric
Flexible
Natural
Operative
Potential
rubbery
soluble
sufficient
suitable
superior
thermoplastic
transparent
b)
Abrasion
Advantage
Dissolution
Elongation
Entanglement
Flexibility
lability
resilience
resistance
reversibility
softness
vulcanizate
c)
Constitute
Formulate
modify
vulcanize
d)
Loosely
Unduly
unusably.
VI. State the key words in the word combinations and translate them into Vietnamese:
1. Abrasion resistance
2. Interchain force
3. Inter molecular motion
4. Melt viscosity
5. Molding process
6. Ozone resistance
7. Processing technique 8. Processing temperature
9. Abrasion resistance materials
10. General purpose rubbers
11. Stress - train properties
12. Styrene butadiene copolymers
13. Ethylene - vinyl acetone copolymer
VII. Translate the following sentences paying attention to the pronoun no:
1. No covalent or chemical crosslinking, that is, no vulcanization or cure reaction is involved in the use of thermoplastic elastomers.
2. No new results have been presented for the stress relaxation of stocks containing black.
3. Thermoplastics contain no gel, and in crumb form, they readily dissolve in conventional rubber solvents.
4. No test can duplicate all the conditions that may occur during natural ageing.
VIII. Translate the following sentences into English:
1. Nh ®• biÕt, ngµy nay c«ng nghiÖp t¹o ra nhiÒu d¹ng nhùa ®µn håi.
2. TÝnh chÊt cña nhùa ®µn håi phô thuéc vµo c¶ ph©n tö lîng cña chÝng còng nh tØ lÖ monome trong m¹ch polime.
3. Ngêi ta ®• x¸c ®Þnh ®îc r»ng, ®é chÞu ozon cña nhùa ®µn håi lín h¬n nhiÒu so víi c¸c polime no b×nh thêng.
4. C«ng nghiÖp ho¸ häc sö dông nhiÒu cÆn th¶i kh¸c nhau ®Ó s¶n xuÊt c¸c ®å vËt cã phÈm chÊt cao tõ nhùa ®µn håi.
5. Tõ nhùa ®µn håi cã thÓ s¶n xuÊt c¸c ®å vËt kh¸c nhau nh: èng chÊt kÕt dÝnh, s¬n, chi tiÕt cña giµy. c¸c ch¸t lµm bÒn,...
6. Ngêi ta tiªn ®o¸n r»ng, nhùa ®µn håi cã thÓ sÏ ®îc øng dông réng r•i rong kü thuËt.
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