Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Chemistry, technology and properties of synthetic rubber. Tutorial
.pdf
conventional thermoplastic are generally suitable for TPEs. TPEs can
also be processed by blow molding, thermoforming, and heat
welding.
Applications
TPEs are used where conventional elastomers cannot provide
the range of physical properties needed in the product. These
materials find large application in the automotive sector and in
household appliances sector. Thus copolyester TPEs are used in
snowmobile tracks where stiffness and abrasion resistance is at a
premium. They are also widely used for catheters where nylon block
copolymers offer a range of softness ideal for patients. Thermoplastic
silicon and olefin blends are used for extrusion of glass run and
dynamic weather stripping car profiles. Styrene block copolymers are
used in shoe soles for their ease of processing, and widely as
adhesives. TPE is commonly used to make suspension bushings for
automotive performance applications because of its greater resistance
to deformation when compared to regular rubber bushings. TPE is
also finding more and more uses as electrical cable jacket/inner
insulation. TPE is also used in some headphone cables.
Trade names
Examples of TPE products that come from block copolymers
group are Arnitel (DSM), Engage (Dow Chemical), Hytrel (Du
Pont), Dryflex and Mediprene (ELASTO), Kraton (Shell chemical
division).
3.23 Thermoplastic Urethane Elastomers
Thermoplastic urethane elastomers (TPAU, TPEU, TPU) is any of a
class of polyurethane plastics with many useful properties, including
elasticity, transparency, and resistance to oil, grease and abrasion.
Technically, they are thermoplastic elastomers consisting of linear
segmented block copolymers composed of hard and soft segments.
181
Chemistry
TPU are formed by the reaction of: (1) diisocyanates with
short-chain diols (so-called chain extenders) and (2) diisocyanates
with long-chain bifunctional diols (polyols). The practically
unlimited amount of possible combinations producible by varying
the structure and/or molecular weight of the three reaction
compounds allows for an enormous variety of different TPU. This
allows urethane chemists to fine-tune the polymer’s structure to the
desired final properties of the material.
Morphology
The final resin consists of linear polymeric chains in blockstructures. Such chains contain low polarity segments which are
rather long (called soft segments), alternating with shorter, high
polarity segments (called hard segments). Both types of segments are
linked together by covalent links, so that they actually form blockcopolymers.
The polarity of the hard segments creates a strong attraction
between them, which causes a high degree of aggregation and order
in this phase, forming crystalline or pseudo crystalline areas located
in a soft and flexible matrix. This so-called phase separation between
both blocks can be more or less important, depending on the polarity
and the molecular weight of the flexible chain, the production
conditions, etc. The crystalline or pseudo crystalline areas act as
physical cross-links, which account for the high elasticity level of
TPU, whereas the flexible chains will impart the elongation
characteristics to the polymer.
These "pseudo crosslinks", however, disappear under the
effect of heat, and thus the classical extrusion, injection moulding
and calendering processing methods are applicable to these materials.
Consequently, TPU scrap can be reprocessed.
Application
TPU has many applications including automotive instrument
panels, caster wheels, power tools, sporting goods, medical devices,
drive belts, footwear, inflatable rafts, and a variety of extruded film,
182
sheet and profile applications. TPU is also a popular material in
Low temperature
mobile electronic device cases such as mobile phones.
Properties
Among the features of commercially available TPU are:
•
•
•
excellent abrasion resistance
outstanding low-temperature performance
excellent mechanical properties, combined with a rubber-like
elasticity
•
•
•
•
high shear strength
high elasticity
high transparency
good oil and grease resistance
The currently available TPUs can be divided mainly in two
groups, based on soft segment chemistry:
1. polyester-based TPUs (mainly derived from adipic acid
esters)
2. polyether-based TPUs (mainly based on tetrahydrofuran
(THF) ethers).
The differences between these two groups are outlined in the
table 20 below.
Table 20.
Main differences between polyester- and polyether-based TPU
(+ + excellent; + good; o acceptable; - poor; - - very poor).
Property
Abrasion resistance ++ 0
Mechanical properties ++ +
flexibility
Heat ageing + Hydrolysis resistance -- ++
Polyester-based
TPU
0 ++
183
Polyether-based
TPU
Continuation of Table 20
Chemical resistance ++ Microbial resistance -- +
Adhesion strength + Injectability ++ 0
In other words, polyether-based TPU is used only in cases
where excellent hydrolysis and microbial resistance is required, as
well as in cases where extreme low temperature flexibility is
important.
When stable light colour and non-yellowing performance are
required, aliphatic TPU based on aliphatic isocyanates is used.
Recently, BASF has pioneered crosslinking during TPU
production, made possible by adding liquid crosslinkers and using a
masterbatch. Plant-based bio TPU has been developed for green
thermoplastic elastomer applications by Merquinsa and GRECO,
marketed as Pearlthane ECO and Isothane respectively.
Trade names
Key commercial brands available are:
•
Epamould, Epaline for extrusion, Epacol for adhesives, Pakoflex
for Synthetic Leather (EPAFLEX)
•
Elastollan (BASF & Elastogran)
•
Pearlthane (Merquinsa)
•
Desmopan (Bayer)
•
Estane (Lubrizol)
•
Pellethane (Lubrizol)
•
New power industrial limited (New power®)
•
Irogran (Huntsman)
•
Exelast EC (Shin-Etsu Polymer Europe B.V.)
•
Laripur (COIM SpA)
•
Avalon (Huntsman)
•
Isothane (Greco)
184
3.24 Styrenic Block Copolymers
These polymers offers many of the properties of natural rubber, such
as flexibility, high traction, and sealing abilities, but with increased
resistance to heat, weathering, and chemicals.
History
It was first made by the chemical division of the Shell Oil
Company in the 1950s and named as Kraton. The earliest
commercial components using Kraton G (thermoplastic rubber) in
the automobile industry were in 1975. American Motors (AMC) used
this polymer plastic for the color matched flexible wheel arch flares
that flowed into rocker panel extensions.
Chemistry
Styrenic block copolymer (SBC) consists of polystyrene
blocks and rubber blocks. The rubber blocks consist of
polybutadiene, polyisoprene or their hydrogenated equivalents. The
tri-block with polystyrene blocks at both extremities linked together
by a rubber block is the most important polymer structure observed
in SBC. If the rubber block consist of polybutadiene, the
corresponding triblock structure is: poly(styrene-block-butadieneblock-styrene) usually abbreviated as SBS. Kraton D (SBS and SIS )
and their selectively hydrogenated versions Kraton G (SEBS and
SEPS) are the major SBC polymer structures. The microstructure of
SBS consists of domains of polystyrene arranged regularly in a
matrix of polybutadiene, as shown in Fig. 14.
Fig. 14. SBS block copolymer in TEM
185
The picture was obtained on a thin film of polymer cast onto
mercury from solution, and then stained with osmium tetroxide.
Properties
The glass transition temperature (Tg) of the polybutadiene
blocks is typically -90°C and Tg of the polystyrene blocks is +100°C.
So, at any temperature between about -90°C and +100°C SBS will
act as a physically crosslinked elastomer. If SBS polymers are heated
substantially above the Tg of the styrene-derived blocks, that is,
above about 100°C, like 170°C the physical cross-links change from
rigid glassy regions to flowable melt regions and the entire material
flows and therefore can be cast, molded, or extruded into any desired
form. On cooling, this new form resumes its elastomeric character.
This is the reason such the material is called a thermoplastic
elastomer . The polystyrene blocks form domains of nanometre size
in the microstructure, and they stabilize the form of the moulded
material. Depending on the rubber to polystyrene ratio in the
material, the polystyrene domains can be spherical or form cylinders
or lamellae. The hydrogenated SBC polymers named Kraton G
exhibit improved resistance to temperature (processing at 200–230°C
is common), to oxidation and to UV. SEBS and SEPS due to their
polyolefinic rubber nature present excellent compatibility with
polyolefins and paraffinic oils.
Applications
SBC polymers are always used in blends with various other
ingredients like paraffinic oils, polyolefins, polystyrene, bitumen,
tackifying resins, fillers to provide a very large range of end-use
products ranging from hot melt adhesives to impact modified
transparent polypropylene bins, from medical TPE compounds to
modified bitumen roofing felts or from oil gel toys to elastic
attachments in diapers. It can make asphalt flexible, which is
necessary if the asphalt is to be used to coat a surface that is below
grade or for highly demanding paving applications like F1 racing
tracks. Kraton based compounds are also popular for use in non-slip
knife handles. Some grades of Kraton can also be dissolved into
186
hydrocarbon oils to create "shear thinning" grease type products that
are used in the manufacture of telecommunications cables containing
optical fibres. Another use is the creation of "gel candles", which can
be formed by dissolving Kraton G1650 into a white-oil (liquid
paraffin) and adding colors if required.
3.25 Copolyether Ester
Thermoplastic polyester elastomer or copolyester elastomer (co-poly
(ether-ester), TPE-E, TEEE, PEEL, COPE).
History
The first studies of polyether-ester block copolymers based
on terephthalate were conducted in the 1950s, companies DuPont de
Nemours and ICI. Polyethylene terephthalate was used as a hard
block in the first studies. However, polyether-ester block copolymers
based on polybutylene terephthalate had more interesting and
perspective properties in terms of commercial use as thermoplastic
elastomers.
Thermoplastic polyester elastomers are commercially
available since 1971 (Hytrel material of DuPont).
Chemistry
Thermoplastic polyester elastomer (TPE-E) is a block
copolymer of polyesters and polyethers or polyesters and polyesters,
they are also called polyether-ester copolymers. Materials have
polyblock structure of (AB)n type.
Industry-produced TPE-Es based on polyesters and
polyethers (polyester-polyether copolymer, ester-ether TPE-E) are
copolymers of polybutylene terephthalate and polytetramethylene
oxide (PBT-PTMO), which are produced under the trademarks
Arnitel E and Arnitel P (DSM), Hytrel (DuPont), Pelprene P
(Toyobo), Riteflex (Ticona), etc.:
C
O
C OOCH2CH2CH2CH2O
C
k
O
PBT (Hard block) PTMO (Elastic Block)
187
C OOCH2CH2CH2CH2O
m n
Belast material (Mogilevkhimvolokno) has a similar
structure.
Material structure includes short rigid blocks of polybutylene
terephthalate and long (m = 1000-2000 and more) elastic blocks of
polytetramethylene oxide. Thermoplastic elastomer contains 20-80%
of hard blocks. At the content of hard blocks over 80% the polymer
is tough impact resistant engineering and industrial thermoplastics.
The molecular weight Mn of commercially available polymers
is 25000 - 30000.
Thermoplastic polyester with rigid blocks of PBT and
rubbery ester blocks (ester-ester TPE-E) are available under the
brand names Arnitel U (DSM), Pelprene S (Toyobo), etc.
Compared with PBT-PTMO these materials have a greater
light resistance, oxidation resistance, wear resistance, but they are
less resistant to hydrolysis and water vapor, as well as impact
resistant at low temperatures.
Properties
Crystallized materials. Maximum continuous operation
temperature: 110-165°C. Melting point: 150-223°C. Glass transition
temperature: -78/+25°C. Long-life cooling functionality up to -55/40°C. Brittle point: -105/-56°C.
TPE-Es have a wide range of mechanical properties
depending on the brand. May be elastic (TPE engineering purposes)
and strong (engineering thermoplastics). Resistant to flexing. High
wear resistance. Resistant to creep. High weather resistance.
Resistant to oils, aromatic and aliphatic hydrocarbons. Resistant to
hydrolysis (stronger than the TPU). Not resistant to concentrated
acids, alkalis, phenols, glycols, cresol, chloroform. TPE-Es are more
thermally stable during processing than TPU, can be painted without
treatment. TPE-Es have low permeability to air, nitrogen, helium,
and propane. Unfilled brands have a high resistance to radiation.
Characteristics of unfilled brands:
Density (23°C): 1.07-1.28 g/cm
3
Tensile strength (23°C): 6-49 MPa
188
Tensile modulus (23°C): 32-1210 MPa
Shore A hardness (23°C): A80-D82
Production
Thermoplastic polyester elastomers are produced by
polycondensation of dimethyl terephthalate (DMT), butanediol
(BDO), or other short-glycols and long chain glycol polyoxybutanediol, polyoxyethanediol or polypropanediol according
to the scheme:
CO
H3C
O
C OOCH
+
HO CH2CH2CH2CH2OH
3
O CH2CH2CH2CH2OHH
+
m
Dimethylene terephthalate Butanediol Polyoxybutanediol
C
O
C OOCH2CH2CH2CH2O
C
k
O
C OOCH2CH2CH2CH2O
m n
PBT-PTMO
Application
Elastic car parts. Interior door handles coating. Door seals.
Damping parts. Anthers. Hinges covers. Track chains of
snowmobiles.
Household appliances. Elastic pads for control panels. Details
of the food processors. Headphones. Elastic parts for industrial use.
Seals of hydraulic cylinders, valves. Vacuum sleeves. Springy and
damping elements. Seals for gas lines. Conveyor belts. Silent gear
wheels.
The handles of hand tools. Details of sports shoes. The soles
of shoes. Sporting Goods. Sport sunglasses frames. Golf Balls (outer
part). Packing. Seals for perfumes. Elastic caps for bottles. Buttons
for clothing. Straps for watches. Flippers.
Trade marks
Belast (PJSC “Mogilevkhimvolokno”)
Arnitel (DSM Engineering Plastics)
Hytrel (DuPont)
189
3.26 Polyester Amide
Properties
Polyester Amide TPE is a transparent elastomeric
crystallizable material. It is a copolymer of polyamide (PA 12, PA 6)
and polyester, it belongs to the group of thermoplastic polyamide
elastomers (TPE-A).
For copolymers of PA 12: mp 134-207°C; Tg -65/-50°C.
Mechanical properties depend on the type and content of the
polyamide. It has high strength and impact resistance.
Characteristics of unfilled brands (for copolymers PA 12):
Density (23°C): 0.96-1.03 g/cm3
Tensile strength (23°C): 29-57 MPa
Tensile modulus (23°C): 40-750 MPa
Light transmission for transparent marks: 80%
Application
Details of sports shoes (soles, etc.). Details of mountain and
ski boots, tennis shoes. Silent gear wheels. Flexible plugs, cable
sheath.
Trade marks
Pebax (Arkema)
Vestamid E (Evonik Industries)
3.27 Thermoplastic Olefin Elastomer
Thermoplastic polyolefin elastomer, Thermoplastic olefin elastomer,
TPO, TEO, TPE-O, o-TPE, c-TPO, CTPO, compounded TPO,
PP/EPDM, PP-EPDM, PP/EP, PP/NBR, PP/POE.
Properties
Crystallizable elastic material. Mixture of polypropylene with
uncured rubber, mainly SKEPT (EPDM), sometimes - with
thermoplastic elastomer (POE). TPO is usually classified as a
material containing more than 20% of rubber, with less rubber the
composition is referred to rubber-modified polypropylene.
190
Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]