Note: Descriptions are shown in the official language in which they were submitted.
l~g~27
BACKGR(~UND OF T~E INVENTION
2 The alkaline-ca alyzed/carDon dioYide bulk polym2riza-
3 tion of 2-pyrrolidone with conversions of 30-40~ or ~ore, is
4 kno~n to produce a hard ~ass which, ~hen chopped, ~ashed and
S dried, is suitable for melt-spin~ing into fibers, or other
6 processing (see U.S. 3,721,652). HoweYer, ~he continuous bulk
7 polyoerization of 2-pyrrolidone under agitat~on produces a finely
8 comminuted prcduct vhich is washed vith ~at~r to remove both
9 unreacted no~omer and the alkaline catalyst. The polypyrrolidone
prod~ct is then i~ the form of a vet po~der containing about 50
11 veight perce~t ~ater, based on polypyrrolidone. This povder is
12 norually dried, but it has too low a hulk density or economical
13 com-ercial prccesi~g, e.g., it is difficult to feed into an
14 e~truder for melt-spinning into fila~ents. Consequently, ths dry
1~ povder is melt-extruded to for~ dense pqllets vhich are suitable
16 for feeding into ertruders i~ melt-spinning processes. In the
17 process of mel~-eYtruding the polypyrrolidone to form dense
18 pellets, its veight a~erage molecular ~aight is degraded from a
19 high initial value of abou~ 200,000, or ~ore, to a value of
35,000-100,OQO or less, because of the well-k~o~n ter.dancy of
21 nylcn-~ to decoapose into its monomer upon ~elting. U.S.
22 3,814,792 ~ses an alcohol~vater solvent a~ elevated teop6rature
23 to dissolve a polypyrrolidone composition for e~trusion. U.S.
24 3,686,066 discusses the ~olding of solid nylon-~ articlos fro~
vatar-svollen polypyrrolidone contaiLing 100~ or more of ~ater,
26 based on the veight of polypyrrolidone, by applying heat and
27 prsscure to the svoll6n ~ass. U.S. 3,324,061 teaches the us~ of
28 elevated teup6ratures and pressures to dissolve polypyrrolidone
29 in ~ater for dry spinning. It is z~ object of the present
in~ention to proYide a means of increasi~g th~ bulk density of
31 polyEyrrolidone vithout substantially degrading its molecular
32 veight.
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6~7
BRIEF SUMMARY OF THE INVENTION
A method for reducing the water content and improving
the bulk density of finely powdered polypyrrolidone, which com-
prises compressing powdered polypyrrolidone, having a water con-
tent of about from 5-60% by weight, at a temperature of at least
about 50C but below the melting point of polypyrrolidone and a
pressure of about from 50 to 300 psi, thereby yielding a solid
polypyrrolidone product having a dry bulk density in the range of
about from 20-50 pounds per cubic foot.
DESCRIPTION OF PREFERRED EMBODIMENTS
The continuous polymerization of 2-pyrrolidone under
agitation, or stirring, produces, at normal conversions, a mixture
of finely divided polymer and unreacted monomer. If the mixture
is washed and dried, the product is a dry powder which is unsuit-
able for further processing because of its low bulk density and
concomitant handling and extruder feeding difficulties. In the
process of the present invention, the fines are washed with water
and dried to reduce the water content of the powdery product to
about 5-60 weight percent water, based on the weight of polypyrro-
lidone, preferably about 10-40 weight percent water, and most
preferably 10-30 weight percent water. This moisture-containing
powder is then subjected to compression under sufficient pressure
and temperature to produce solid polypyrrolidone having a suitable
bulk density for feeding an extruder in a melt-spinning process.
The maximum temperature of the polypyrrolidone during
compression is always well below its melting point; consequently,
degradation of the polymer to monomer does not occur rapidly. The
monomer content of the dried product of this process is normally
less than about 0.2 weight percent, which is appreciably better
than that obtainable from melt-extrusion pelletizing of the pow-
der without further treatment. The temperature selected for the
polypyrrolidone during compression is inversely proportional
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3627
1 to its ~ater content. At the lo~sr ~ater conts~ts employed,
2 about 10~, highQr temperatures of about 150C or greater ar~
3 preferred. At the higher ~ater contents employed, about 40~,
4 lo~er temperaturas of 100C or less may be utilized, i.e., e~en
as lo~ as about 50C. Generally, maYimUm te~peratures of about
6 75~-225C, preferably about 100-200C, and pressures of 50 psi-
7 300 psi are preferred for compression densification of polypyr-
8 rolidone in this process. The moisture content of the compressed
9 polymer is generally in the range of 5-40~ by ~eight based on
polypyrrolidone. This moisture is removed by drying at
11 temperatures of about 100-15~C, and optionally, under rsducad
12 pressures of a~out 1-5 torr.
13 The polypyrrolidone po~der which rorms the starting
14 material of this process may be any particulate product of polym-
erizi~g or copolymerizing 2-pyrrclidons. Preferably 90 weight
16 perce~t of the powder is of screen size greater than about ~o.
17 200 ~0.07 m~) U.S. Standard Sieve and lsss than about ~o. 3 ~6
~, ,
18 on) U.S. Standard Sieve, more pr~ferably No. 40 (0.4 mm)-~o. 10
19 (2 mm) U.S. Standard Sie~s. The product of this process is
~haracterizsd as solid polypyrrolidone having a dry bulk density
21 suitable for melt-spinning, that is, a bulk density of about 20-
22 50 lbsfft3, i.e. 20-50 x 0.016 g~cc, or about 0.3-0.8 gfcc,
23 preferably about 30-50 lbs~ft3 a~d most preferably about 40
2~ lbs/ft3. `"Dry bulk der.sity" refers to the bulk density of the
solid polypyrrolidone having a water content of less than about 1
26 ~eight percent. The product is obtained as pellets, or kibbles,
27 fro~ a p~llet mill, or as sheets o, films from a 2-roll mill,
28 having any shape or thickness suitable for later comminution,
29 drying and processing. The moisture content of the dried
compressed polypyrrolidone ~ill usually ~ less than about 1
31 ~eight percent, pre~erably less than abou~ 0.5 ~sight percent.
;'
,
1 Com~osite products, useful for later processing, can be provided
2 by adding materials such as other polyamides, e.g., nylon-6,
3 pigments, vhiteners, e.g., such 2S tita~ium dioxide, anti-
4 oxida~ts, ultra-violet sta~ilizers, thermal stabilizers, such as
the epoxides, etc., etc., to tha ~et powder bsfore comprsssion.
6 As discussed above, the kibhle prodQct, of the present
7 process, has an improved bulk density ihich facilitates melt
8 extrusion spinning. This improvement also, of course,
9 facilitates melt extr~sion, in ge2eral, regardless of the
particular extrusion product. Thus, for eYampls, the present
11 invention also facilitates the melt extrusion of films, sheets,
12 configured articles or, if desired, e~_n diffarent sized or
13 shaped pellets, etc. The kibble product further has vastly
14 improved ganeral handling charact~ristics as compared ~ith the
initial poly-2-pyrrolidone powder.
16 EX E NPLIFICATION
17 Ex_mE~ 1
18 Polypyrrolidone po~der of 170,000 ~eigh~ average
19 molecular ~eight, co4taining 22~ by ~eight of ~ater, ~as
compacted by forcing the po~der through the holes of a die of a
21 kibble mill. The size of the holes was 1/8 inch in diameter by
22 1-1/2 inch long. The po~dsr was heated by mechanical mixing,
23 used i~to a hardened cylindrical shaFe and cut into 3/16 inch
2~ lengths at the die holes by a doctor blade. Ki~ble temperatures
~ere about 80C as measured by a thermoms~er in the receiver. A
26 smooth surfaced kibble ~ith irregular ends and 19~ water content
27 was thus formed. The bulk de~sity of the kibble vas 37 lbs/ft3
28 after drying to less than 0.1 weight percen~ ~ater. The
29 molecular weight o the kibble ~as the same as that of 'he
polymer powd~r fed to the mill.
ExamPl--2
2 Polypyrrolidone powder or 290,000 wsight average
3 ~olecular weight (10-200 mesh~ coniaining 37 weight parcent wzter
4 (bas~d on polypyrrolidone) was su~jected io compac~ion by passing
S it through a 2-roll mill. Roll surface temperature was about
6 148-1~4C. A polymer was compress~d into dense sheets
7 approximately 1/16-3~32 inch thic~ which had 19% ~ater content.
8 The sheats wera chopped into approximately 1/8 inch by 1/8 inch
9 granules and dried. The particle density of these granules was
approximately 62 lbs/ft3 and the average bulk density vas about
11 32 lbs/ft3. The ~olec~lar weight of the granules was identical
12 to that of the starting polymer po~der.
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