Note: Descriptions are shown in the official language in which they were submitted.
3~
TITLE
Polyvinyl Alcohol Dust Suppression
by Admixing Polyglycol
BACKGROUND OF THE INVENTIO~
The subject invention relates to the
suppression of dustiness inherent in certain
polyvinyl alcohols, hereinafter PVA, by contacting
the PVA with a low concentration of a water soluble
polygl~col.
Various methods for controlling dust in a
normally high dusting material are ~nown. For
example, it is known to mix a high dusting powder
such as antimony vxide with less than about 1 percent
by weight polytetrafluoroethylene to form a dry,
dust-free mixture. Further~ a method for controlling
the dustiness of water insoluble alkali metal
carboxylate salts is known whereby the salts are
i~termixed with fumed silica or fumed alumina
particles.
The preparation of a substantially dustless
powdered composition of spray-dried acrylic resin is
known whereby a dedusting amount of one or more
organic alcohols selected from the group consistin~
of 2-he~adecyl alcohol and iso-tridecanol, is added.
Also known is a process for the reduction of
dissemination of fugitive dust particles into the
AD-5181 atmosphere by treating the particles with an aqueous
solution of octylphenoxy polyethoxy ethanol and a
copolymer of ethylene oxide and propylene oxide. A
satisfactory process for dedusting PVA has yet to be
disclosed.
SUMMARY OF THE INVENTION
The subject invention is a process for the
preparation of a substantially dust-free PVA powder
comprising contacti.ng the PVA with about 0.5 percent
~2''~
~1
!~ ~ ,, -.
.. ... . . . .
3~
~o ~bout 4.0 percen~ polyglycol and the product
therefrom. A11 percentages reported herein, unless
otherwise specified, are weight perc ntages.
~ ING
The Figure is a graphical representation of
the effect of poly~lycol concentrations on the
dustiness of PVA.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The PVA to be treated by the process of the
subject invention has a viscosity OL 2 to 125 mPa~s
as measured on a 4 percent aqueous solution at 20C
by the Hoeppler falling ball method (ASTM~D 1343 56)
and a degree of hydrolysis or alcoholysis of at least
80 mole percent, including its copolymers. For a
more detailed discussion of PVA, see U.S. Patent
4,119,604 assigned to E. I. du Pont de Nemours and
Company,
The dustiness of PVA is caused by fine
particles formed when dissolved polyvinyl acetate is
hydrolyzed or alcoholyzed to ~VA or when the PVA is
attrited to yranular form. The advantages for
certain high fines polyvinyl alcohol in relation to
water slurrying and solvation properties are well
established; however, inherent in high fines PVA i a
dustiness resulting in worker unpleasantness.
Attempts made in the past to mix various additives
with polyvinyl alcohol to improve end use pPrformance
have met with difficulty due to the limited
compatibility of PVA with most additives. This
incompatibility is typically exemplified by the loss
of aqueous solution or film clarity, film-forming
ability, ,and tensile strength. It is the object of
this invention to reduce the dustiness of PVA while
retaining the advantageous wa~er solubility
properties of the small particle size (high fines)
e L~
product and to accomplish this with no detximental
modifications to the physical film or solution
properties of the original polyvinyl alcohol. The
subject inven~ion agglomerates these fines during or
S af ter PVA production by adding a polyglycol to the
PVA production stream. The polyglycol can be used
either 2S a solid, dissolved or dispersed in a fluid,
or as a liquid. By agglomerating the small PVA
fines, the overall particle size distribution i5
shifted toward the larger and heavier particle size
fractisns, thereby reducing the ~uantity of fines
which may remain s~spended in the atmosphere during
handling, hence încreasing the overall PVA yield.
This mixing of the PVA and polyglycol can be carried
out in any conventional manner, for example, blade
mixing, fluidized bed mixing, mill mixing or solvent
system mixing, as long as the mixing results in
intimate contact between the polyglycol and the PVA.
The dedusting additive, polyglycol, is
defined as polyethylene glycol or methoxypolyethylene
glycol haviny a molecular weight of about 200 to
14,000 and an oxyethylene content of 3 to 400 moles
with the polyethylene glycol having the general
formula HOCH2~CH2Oc~)ncH2oH- The
preferred polyglycol is a polyethylene glycol having
a molecular weight of about 600 due to its superior
dust suppressant properties after extreme temperature
recycling. Block copolymers containing the
constituents of polyethylene glycol with propylene
oxide in which the oxyethylene content predominates
~more than 50 percent) are, to lesser extent,
suitable as long as the end-use properties of the PVA
are not adversely affected. The moleculax weight of
these copolymers ranges from about 1000 to 14,000.
~3~
The physical nature of polyglycols makes
them especially suited to act as a dust suppressant
for PVA. The ready cold water solubility of
polyglycols ailows the agglomerated fines to retain
PVA water solubility. The polyglycols do not reduce
the tensile strength of films traditionally produced
from PVA. Further, although the polyglycols remain
on the surface of the PVA particles, they do not
introduce deleterious surfactant activity into end
uses for PVA. Surpri5ingly, as exemplified below,
other compounds generally grouped with polyglycol as
plasticizer additives for PVA including glycerin,
water, diethylene glycol and dibutyl phosphate are
found to be relatively ineffective as dust
suppre~sants for PVA.
The dustiness of PVA is determined by either
of two tests. In the first test, an amount of
PVA/polyglycol mixture is added to a cylindrical
glass jar so that the jar is about half-filled.
After tightly covering the jar~ the sample is
inverted and immediately returned to its upright
position. The amount of time necessary for the PVA
fines to settle out of the upper half of the jar,
;i.e., suspension time, is measured in seconds. For -
purposes of the subject invention, a dust-free P~JA is
achieved when the suspension time is 3 seconds or
less. In contrast, the second test determines the
weight percent of free dust fines of PVA that can be
eluted from a 150 gram PVA sample with 4.7 x
10 4 m3/s (1 cfm) of air in 5 minutes. For
purposes of the subject invention, a 50 percent
reduction in percent dust is desired in order to
impart a noticeable improvement at manufacturing
scales. Both test~s are more fully explained in the
examples t:hat follow. This dedusting is achieved by
contacting about 0.5 to 4.0 percent polyglycol and,
more preferably, about 0.5 to 2.0 percent polyglycol
with the PVA. These ranges were derived according to
~ the procedure of Example IV, fully explained
therein. The contacting is carried out at a
temperature where the polyglycol is in a liquid state
but not so high that the PVA is subject to
degradation, i.e., a range of about ~ C to 150C.
The contact time that is necessary to achieve a
homogeneous mix between ~he polyglycol and PVA is
that time sufficient to achieve at leas~ 50 percent
reduction in dust, generally at least 5 minutes~
EX~MPLE I
~ I . ~_
Various polyglycol dust ~uppression
additives were added to PVA (Elvanol~ 71-30, a fully
hydrolyzed PV~ con~aining 100 percent polyvinyl
alcohol units manufactured by E. I. du Pont
de Nemours and Company and Gelva~ol~ 20-30 sold by
Monsanto Chemical Co., an 86-89 percent hydroly2ed
PVA) to agglomera te the PVA f ines . All samples were
prepared by heating the granular PVA to a temperature
above the melting point of the additive (about 65~C)
in a Readco Sigma Blad~-mixer, manufactured by Read
Co., York, Pa., and then all~ing he additive to mix
25 with the P~A for abol~t 30 minutes ~o obtain
homogeneity. The degree of dustiness of the mixture
was determined by placing a 150 ym sample in a 9.46 x
m3 (1 quart) cylindrical jar and inverting
the jar with the suspension time of the f ines
measured in seconds. The suspension time for virgin
PVA was measured as a control. The result~ are
tabulated below,
*denotes t~ade ~ark
.,
~91~
COMPOSITION
(% additive based SUSPENSION
on~ 2~ PVA~
A. Virgin PVA 6 seconds
B. PVA ~ 1.0% Pluronic~ F.~8,
manufactured by BAS~
Wyandotte, Parsippany, NJ, and
comprised of ethylene oxide/
prvpylene oxide copolymer
containing 80% ethylene
oxide unitsO 2 seconds
lG
C. PVA ~ O.5~ Carbowa~ 6000 manu
factured by Union Carbide, NY,
NY, and comprised of repeating
. oxyethylene units ~erminated
by a hydroxyl group . 2 seconds
D. PVA ~ O . 5~ Carbowax~ 6û0 also
lS manufactured by Union Carbide,
struc~urally identical to
Carbowax 6000. 2 second s
E. 86-89~ hydrolyzed PVA
(Gelvatol~ 20-30 Monsanto)
a~trited to a suspension time
~0 of 4 seconds ~ 0.5~ Carbowax 600. 2 seconds
Th is example is to illustrate tha~ a
polyglycol with a molecular weight of about 600 is
preferred due ~o its retention of dus~ suppression
properties after ex~reme temperature cycl2~.
PVA (Elvanol~ 71-30, E. I. du Pont
de Nemours and Company) was admixed in a sealed jar
with polyglycols having the molecular weights listed
below. ,After 20 minutes mixing on a roll mill, the
samples were exposed to a temperature of 90~C for 1
hour and ~ubsequently at -7C for 4 hours.
Suspension times were measured at ambient
temperatl~res .
3~
COMPOSITION
(% polyethylene Suspension Suspension
glycol, PEG, Molecular Time After Time After
based on w~ight Wt of 1 H~ur 4 Hours
f PVA~ - PEG ~ Z~ _
PVA ~ 0.5~ PEG 600 2 seconds 2 seconds
" 1000 " 3 seconds
200~
000 " "
~ ~iO~O " "
1~ 8000
PVA ~ 1~ 0~ PEG 600 . n 7 seconds
6000 " 3 ~econds
This example i5 l:o illustrate that compounds
generally grouped with polyglycol as plasticizer
additives for P~A are ineffective as dust suppressing
additives for PVA. Also included i8 quantitative
data to show that polyglycol with a molecular wei~h~
of 600 is preferred over a polyglycol with a
molecular weight of 6000.
Several liO gram samples of PVA (Elvanol~
71~30, E. I. du Pont de Nemours and Company~ were
prepared by admixing the varic~us additives :Listed
below for abou~ 20 minutes on a roll mill and ~ested
~5 for dustiness. A control sample of PVA was also
te s ted .
The dustiness of the samples was determined
quantitatively as the weight percent of free dust
fines of PVA that could be eluted from the PVA with
30 4 . 7 x 10-4 m3/s tl . 0 cfm) of air in 5 minutes
using an open ACE* B (70-100 micron) porosi~y
fritted funnel as the sample receptacle. The results
are tabulated below.
*denotes trade mark
3W
Additive Percent Dust
None 8.3
2.0% polyethylene glycol
with mol wt of 600 as per the
subject invention 2.0
5 2.0% polyethylene glycol
with mol wt of 6000 as per the
subject invention 3.2
2.0% glycerin 6.7
2.0% diethylene glycol ~.2
10 2~0% dibutyl phosphate - 5.~
2.0% alkyl aryl polyether alcohol 5.1
EXAMPLE IV
This example is to illustrate that the
addition of less than about 0.5 percent polyglycol
does not adequately eliminate the dust from PVA, and
that the addition of greater than about 4.0 percent
polyglycol to PVA does not increase the dedusting of
the PVA.
The same procedure used in Example III was
used here. Two samples of PVA were used, Sample A
registering 8.3 percent dust in accordance with the
procedure of Example III before polyglycol treatment,
and Sample B registering 11.5 percent dust. These
samples were chosen to determine the lower and upper
limits oE percent polyglycol necessary to suppress
the du~tiness of PVA. 5amples with greater than
about 12 percent dust, after addition of more than
about 3 percent polyglycol, displayed particle
massing and, hence, could not be fluidized,
30 inhibiting handling of the PVA during plant
manufacturing processes. The samples were treated
with increasing amounts of polyethylene glycol,
molecular weight 600. The results, tabulated below
and graph.i.cally illustrated in the Figure, show that
35 less than about 0.5 percent polyglycol did not
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adequately eliminate the dust rom the PVA, i.e., did
not eliminate 50 percent of the dust. Further, the
largest quantity of polyglycol needed to completely
suppress the dustiness of a PVA sample was evidenced
by Sample B which registered 11.5 percent dust before
polyglycol treatment. In that case, between 3 and 4
percent polyglycol was added before the PVA lost
~luidity completely~ The shaded area of the Figure,
therefore, serves to define the lower and upper
limits of the percent polyglycol necessary in the
practice of the subject invention~ i.e., 0.5 to 4.0
percent based on the weight of the PVA.
Sample A represents a fines content in PVA
most commonly found commercially. As ~een by
reference to the Figure, greater than about 2.0
percent polyglycol does not further decrease the
percent dust in the PVA. Therefole, a preferred
amount of polyglycol required to eliminate dust in
such a PVA is 0.5 to 2.0 percent.
Percent
polyethylene glycol Percent
(600 mole wt) __ Dust
0.0 8.3
0.8 2.9
25 2.0 2.
3.0 1.9
5.0 1.9
6.0 1.9
,~
3~
~a~
Percent
polyethylene glycol Percent
~600 mole wt) Dust
_ _ _ ____
o,o 11.5
1.0 7-5
2.0 ~-5
3.0 2.5
3.5 2.~ (loss
of fluidity)
EXAMPLE V
This example is to illustrate that
p~lyglycol does not adversely affect the end-use
proper~ies oP PVA when cast into film form from
aqueous solution, while other compounds generally
grQuped with polyglycol as plasticizer additives for
PVA reduce the tensile stren~th of such a film.
Aqueous solutions of PVA (Elvanol~ 71 30,
E. I. du Pont de Nemours and Company) containing the
various additives listed below were cast from aqueous
solutions onto a glass plate, air dried 24 hours and
conditioned for 48 hours at 21C and 50 percen~
relative humidity prior to Instron ~esting.
The breaking tensile strength was determined
according to the following procedure: a 2.5 cm wiàe
by 2.2 mil ~hick sample was pulled by the jaws on an
Instron*tester at ~ rate of 5 cm/min with an initial
jaw separation of 2.5 cm. The 'censile strength
re~istered at break was averaged for 5 samples.
The tensile strength of film produced from untreated
PVA is 77 x 103K~a.
The results are tabula~ed below.
*deno.tes t~ade maxk
3~
dd i t i v e _ i l e
O ~ 8~ polyglycol (mol wt ~600) 77 x 103 KPa
2 . 0% " " 77 x 103 KPa
2.0% glycerin 70 x 103 KPa
2 . 0~ diethylene glycol 70 x 103 KPa
2~ 0% dibutyl phosphate film unobtainable
due to loss of
wetting properties
lQ
11
