Gel-spun high-performance polyethylene fibres

Introduction• Gel-spun polyethylene fibres are ultra-strong,

high-modulus fibres that are based on the simple and flexible polyethylene molecule.

• They are called high-performance polyethylene (HPPE) fibres, high-modulus polyethylene (HMPE) fibres or sometimes extended chain polyethylene (ECPE) fibres.

• The gel-spinning process uses physical processes to make available the high potential mechanical properties of the molecule.

• The chemical nature of polyethylene remains in the gel-spun fibre and this can both be positive and a limitation: abrasion, flexlife, etc. are very high but the melting point is sometimes too low for certain applications.

Manufacture• Gel-spun high-performance polyethylene fibres

are produced from poly-ethylene with a very high molecular weight (UHMW-PE).

• This material is chemically identical to normal high-density polyethylene (HDPE)

نظیر • باال، مدول و باال استحکام الیاف از دیگر بسیاری خالف برای میله و ساخت بسیار مولکولهای دارای پلیمر این آرمیدها،

. نمیباشد شکل

• In aramids and comparable fibres, the molecules tend to form rod-like structures and these need only be oriented in one direction to form a strong fibre.

• Polyethylene has much longer and flexible molecules and only by physical treatments can the molecules be forced to assume the straight (extended) conformation and orientation in the direction of the fibre.

Gel spinningpolymer

• High performance polyethylene fibres are

commercially produced under the trade names

Dyneema by DSM High Performance Fibers in the

Nether-lands and by the Toyobo/DSM joint venture

in Japan, and Spectra by Honeywell (formerly

Allied Signal or Allied Fibers) in the USA.

• To make strong fibres, the molecular chains must

be stretched, oriented and crystallised in the

direction of the fibre.

• Furthermore, the molecular chains must be long

to have sufficient interaction and for this reason

polyethylene with an ultra-high molecular weight

(UHMW-PE) is used as the starting material.

Gel spinning process

• spinning these fibres from the melt is almost impossible

due to the extremely high melt viscosity.

• Furthermore, the drawing of a melt-processed UHMW-PE

is only possible to a very limited extent owing to the

very high degree of entanglement of the molecular

chains.

• Melt-processed UHMW-PE can be drawn up to five times

only.

• . اثر در میگردند مرتفع مشکالت این دو هر ریسی ژل فرآیند در . میگردند باز هم از ها زنجیر حالل، در شدن حل

(disentanglement )

زیاد • بسیار کشش آنها به ریسی ژل حین در میتوان نتیجه در. نمود اعمال

( ۵۰-۱۰۰) کشش واحد

•. شد خواهند یافته آرایش شدیدن زنجیرها زیاد، کشش این اثر در

الیاف • تولید منطق، این اساس از Dyneemaبر تجاری طور به

.۱۹۹۰سال گردید آغاز هلند در

• The production of Dyneema fibres demands

relatively little energy and uses no aggressive

chemicals. The product can easily be recycled so

environmental pollution from product and process

is minimal.

• PE with Mw = 1.5 • 106 was stabilized with 0.5%

by weight di-t-butyl-p-cresol (DBPK) at 150 0C,

then dissolved with 2% by weight in decaline at

130 0C, and spun through spinneret holes of 0.5

mm diameter according to the air gap process

into a bath of decaline and water at 10 0C,

extracted over a long distance, and drawn at 140

0C in a hot air oven.

• After a draw ratio of 1:32 the multifilament has an elastic modulus of 90 GPa, a tenacity of 3.0 GPa (=36.5 g/dtex) and 6% breaking elongation.

• The draw ratio is also dependent on the

temperature and the type of drawing: Wet

drawing is limited to about 1:60, while hot air

drawing has achieved ratios of 1:90.

• While the better solvent is decaline, paraffin oil is

technically preferred, especially for working

around 180.. .200 0C. Then the drawing is divided

into a first stage of 1: (2. . .4) directly following

the coagulation bath, a second stage of up to

1 :12 after extraction, and a third stage after

drying at 180.. .200 0C in hot air with drawing over

a long heated plate at > 130 0C.

In the autoclave (10) the

solvent (11) and the stabilizer

(12) are mixed and heated for

the paraffin oil to 140.. .170

0C. In the high shear mixer

(15) the PE powder is pasted

with this and homogenized in

the twin screw extruder (18).

This gel is then extruded by

the spin pump through the

spin head (23) into an air gap

before the filaments enter into

the coagulation bath (30).

During take-up there is a hot

air drawing zone between the

godets (54) and (59). A long

distance extraction (37)

follows and so does hot air

drying (45). This yarn can

either be wound (52) and

taken up from this bobbin, or it

can be hot drawn

پلی • ساختار در ممکن مولکولی بین نیروی تنها اینکه به توجه باپیوند ایجاد جهت میباشد، واندروالس ضعیف های پیوند الفینهازیاد المقدور حتی مولکولی وزن باید قوی، زنجیری بین های

باشد.

به • مستحکم، بسیار اتیلنی پلی الیاف تولید برای علت، همین به. است نیاز میلیون یک از بیش مولکولی وزن با مری پلی

مولکولی • وزن با پلیمری از .۶-۲غالبا میشود استفاده میلیون

مولکولی • وزن از بیشتر بسیار مولکولی وزن . HDPEاین میباشد

در • پلیمریزاسیون حدود HDPEدرجه در ۱۸۰۰-۷۰۰در است،در فاکتور همین ۲۵۰،۰۰۰-۱۰۰۰۰۰بین UHMWPEحالیکه

میباشد.

محلول • غلظت بایستی اقتصادی، نظر نقطه از دیگر طرف از. باشد ممکنه حداکثر ریسندگی

• these two factors together result in a solution that has a viscosity that is far too high to spin.

• Already at 2% PE concentration in paraffin oil viscosities of up to 20,000 Pa- s can occur.

Gel spinnigGelation and crystallization

• The solvent used in the polyethylene gel-spinning

process should be a good solvent at high

temperatures (>100 °C) but at lower

temperatures (<80 °C) the polymer should easily

crystallize from the solution.

• After the spinneret, the solution is cooled in the quench, the solvent is removed and a gel fibre is formed. This can be done by evaporation or by extraction of the solvent.

• From a diluted solution, polyethylene crystallizes

in the form of flat crystals of about 20 nm

thickness, in which the chains are neatly folded.

• In these crystals the C-axis or chain axis is

perpendicular to the crystal (lamella) surface.

• The crystal structure is orthorhombic, which

implies that the crystal axes are at right angles,

two by two.

Fibre characteristics• Dyneema and Spectra are produced as a

multifilament yarn.

• The titre of the monofilaments varies from about 0.3 denier per filament (dpf) (0.44 dtex) to almost 10 dpf (11 dtex).

• Tenacity of one filament may well be over 5 N/tex, and the modulus can be over 120 N/tex.

• Most fibre grades have a more or less circular cross-section. The fibre skin is smooth.

• HPPE fibres have a density of 970 to 980 kg/m , typical for highly crystalline linear polyethylene.

• Dyneema has a melting point between 144 and 155 °C, depending on the conditions,

الیاف • این زیاد، بسیار استحکام و کم بسیار دانسیته به توجه باآنها تناسیتی طوریکه به میباشند، زیاد العاده فوق تناسیتی دارای

حدود نیز ۱۵-۱۰در آنها مدول و بوده مرغوب فوالد الیاف برابرنظیر ای پیشرفته فوق الیاف با فوق PBOتنها کربن الیاف و

. است مقایسه قابل باال مدول

• In contrast to the high tensile strength, the gel-spun fibre has a low compressive yield strength, approximately 0.1 N/tex.

fatigue• HPPE fibres are the first high-performance fibres

that not only have a high tenacity but that also have tension and bending fatigue properties comparable with the commonly used polyamide and polyester grades in ropes.

• Fatigue is very important in, for example, rope applications.

• Carbon fibres and glass fibres have a high

modulus and a brittle breaking mode, but

Dyneema and Spectra fibres have a high modulus

but still are flexible and have a long flex life,

Abrasion resistance

• This fiber has a very low coefficient of friction; is

self-lubricating; and is highly resistant to abrasion,

in some forms being 15 times more resistant to

abrasion than carbon steel.

• Its coefficient of friction is significantly lower than

that of nylon and acetal, and is comparable to that

of polytetrafluoroethylene (PTFE, Teflon), but

UHMWPE has better abrasion resistance than PTFE.

Chemical Properties• It is odorless, tasteless, and nontoxic.

• HPPE fibres are produced from polyethylene and do not contain any aromatic rings or any amide, hydroxylic or other chemical groups that are susceptible to attack by aggressive agents.

• The result is that polyethylene and especially highly crystalline, high molecular weight polyethylene is very resistant against chemicals.