Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3 '1.~3~
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lile pres~,lt inven~ion re,a~es ~o microemulsions of
wa~er~ oi7 (~/'û~ ~ype and to tfleir use in the treatment of
paper produc~s.
More ~ar~icularly, t~e present invention relates to W/0
microemulsions con~ainirly alkali meta7 and alhaline earth
metal sa~ts, and to their ùse for deacid;fy;ng paper and
pa~e~ produclx, such as books, drawings, paintings on paper
an~ prin~inys.
Paper is knowrl to undergo degradation over time. The
mos~ impor~arl~ factor among those factors which cause paper-
ùegrada~ion is the acidity present in paper products.
Sucn acidity may have several origins, such as, for
example:
-- ~ne acidic charac-ter or hydrolys;s of add;tives used in
~aper manufactor;ng process; and
-- the conver-sion of air pollutànts adsorbed by paper (e.g.:
SU2) into strong acids (H2SG4);
-- lignine degr-adation;
-- oxidation of cellulose and hemicellulose dur;ng bleach-
ing, or during the course of natural ageing.
In ar;dic paper, ageing causes discolouring
(yellowing), brittleness, and, in general, loss of
mecnanical properties of the paper. These effects are more
serious if paper contains a large amount of lign;ne.
The acid-catalysed degradation process of paper
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produc~s carl be s~opped by dear_idificatiorl.
The most widely used deacidification process is based
or~ e pre~ipitation of an alhaline buffer on the cellulosic
fivres of paper ~W.J. ~arrow, Restoration methods; Society
oi` American Ar-c;nivists, Richmorld, Virginia, ~ct. 27, 1942).
The ~heets are soaked in a solution of calcium hydroxide,
whi~rl neu~rali~es the acids presen~; residual calcium
rhy~rvxide is subsequently conver~ed into carbonate by means
or a b;carvo~la~e soiu~ion. Carbonate deposited on paper
~u~)plies an alhalirle r-eser-ve which, during a certain time
periou, neutr-ali~es the acids coming from same paper and
from 5Ur roundirlg environment.
unfortuna~ely, this process cannot be applied for a
bulk tr-eatmen~ OT books, because these must be previously
disassembled into individual sheets, and the individual
snee~s must be treated and dried one by one.
~ urthermore, the use of such an aqueous solution
causes, during the drying, the bonding of pages and the
swelling of paper fibres.
The trend in the development of processes for paper
deacidification was therefore one of depositing substances which may supply
an alkaline buffer, while avoiding use of the aqueous vehicle.
~ a-A-2 18û 248 discloses an expensive process for paper
pruducts preservation, in which a polymeric film is coated
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,i,e me~r~ou ~isclosed in u.S. pa~ent 4 ~22 &43 uses a
~s~lena ion uorlsL i ~u~ed b y sa l~ts of basic metals and a
su~u~ior) eonl~osed by an inert halogerlated hydrocarbon an~ a
~vrTde~dr)~. urlfor~urla~ely, ~he me~hod requires the use of
IJ9~n~ O nydr oc;a r r)Or~S, Wil i~1 ar e nox ioUS and pollutan~.
T;le ~r~;es~ d isclc~seu in U.S. patent 3 676 055
pr u~eses a po~ r ea~merl~ for acidic books. According to this
~"~ "e ~o~ks are first dipped in a solution or
~s~er-siorl coln~osed by alkali metal and alkal;ne earth metal
o~ides, arlri an or-garlic solvent. Subsequently, for the end
pr-eser-va~ion treatment, a solution of alkyl oxides, or of a
mixture of alkyl oxides under pression developed by a
propeilarlt (Freon 12j -is used.
,his process suTfers from the following drawbacks:
-- two treatmenl sie~s;
-- inK migra~ion; and
-- ~ne use of Freorl ~i.e., a halogenated hydrocarbon), which
causes the process to be environmentally unfriendly.
in another_ process (G. ~elly, Non aqueous
deaeidificatiorl of Books and Paper in Conservation of
Library and Archive Materials and the Graphic Arts (G.
i-etherbridge, ed.), London, Butterworths, 1987, page 117)
~ne dried books are impregna~ed with diethylz;nc vapors at
3 ~
` c . L) i y ~ rly i ~ ; r)~u l r ~ es ~h~ ~c i d i t y ~nd i s ~ nver ted,
wn~ r- du~or i)s ~;he nor~ noisture amount, into zinc
'J, io~, i,r)US l~avirl~ ~n a~h~line reserve.
The ~)ru(~es~ re~luir-e~ ~ very deep pre-drying because
~ne react ion ~el,ween w~er ~nd die~hilzinc is very fast; this
~r e-~ir y i rly c~ r-~ ion migr~t, c;i~u~;~ d~mages to paper produc~t.
rur t,herlnore~ in the presence of oxygen, diethylzinc is
iv~ d ~ro~:~3s~ ~;e~y conditions mus~ be carefully
uor~ (~r ~i i e~ .
~c i d ,o~er- ean b~ d~ac; i d i f i ed al so i n gas phase . Such a
~o~ isclc~s~ in U.S. p~tent 4 619 735, which use~
~mirles, such as mel~mine derivatives. Unfortunately, this
process results in the likelihood that a low alkaline reserve will be found, andfurthermore causes paper yellowing and displays toxicity risks.
Therefore, the object of the present invention is to obviate or mitigate at
least one of the disadvantages of the processes known from the prior art and
to provide a relatively low-cost product and process for deacidifying paper and
paper products in bulk, which process renders such paper products resistant
to the effect of acids present in paper and/or deriving from surrounding
environment.
The present Applicant has found now that the use of a microemulsion
makes it possible to deposit an alkaline reserve and consequently protection of
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paper to be achieved, with a relatively simple, low-cost and environmentally
friendly process, because only surfactants are used, which Can be recovered
at process end.
"Mi~;roemulsion" means a dispersed system of oil-in-
wa~er or- wa~er-in-oil. "Oil" means a hydrofobic, water
immiscible liquid.
These microemulsions are very stable, clear systems.
Ine stari1i~y of mi~;roemu7sions ix obta;ned by us;ng
surfa~;~an~s (an~l, possibly, co-surfactants) which form a
s~a~ er monolayer ar-ound dis~ersed water droplets.
The clearness results from dispersed droplets being of
srnall. size (~û-1~ûO A~.
Tne use of a microemulsion of water-in-oil ~WiO) type
as the vehicle Tor deac;dify;ng substances of paper d;splays
two advantages:
-- Owing to the small amour-t of water contained in the
emulsion, it does not cause the fibres to be swollen;
-- No pr-oblems ar ise during the drying step, because the
i s pe r se n t p hase i s vo 7 a t i 1 e .
Therefore, in one of its aspects, the present invention provides a
microemulsion of water-in-oil type containing the following components:
(a) an aqueous solution of alhal i metal and/or ellkal ine
earth met~l :;al ts soluble in water in dispersed ph~lse,
(b) a hydrophobic dispersant agent in continuous phase,
6 ~1 3
(~,) di~ ~ec~, One surTdc~arlt ayerl~:.
In another of its aspects, the present invention provides a microemulsion
of water-in-oil, characterized in that its essential components are the following:
a~ 1-3û~ by we-igh~ of a 10 3 - 1G M aqueous solution of
water-soluble alkali metal and alkaline earth
me~al salts,
b~ 5û-95% by weight of a hydrofobic organic solvent as the
d i sper san~ agent,
( (.: ) 1 -4U~ y we i ght of at 1 east one non- i on i c or i on i c
surfactant.
When an ionic: surfactant is used, the microemulsion
possiL)ly compr ises from 1 to 20s6 by weight (based on
surfactant) of an organic co-surfactant.
Particularly preferred accord;ng to the present
inven~ion is a microemulsion containing 6-lû~ by weight of a
lû-- - 1û-~ M aqueous solution of alkali metal and alkaline
earth metal saits, 70-90% by weight of a hydrophobic solvent, 5-25% by
weight of a surfactant.
I n the m i c roemu l s i on accord i ng to the present
invention, water is used in order to act as the vehicle for
the alkalating agent, therefore the amount of water used in the process is really
kept at a minimum.
The salts of alkal i metals and alkal ine earth metals
used in the emulsion according to the present invention can
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a
~ o~iues, ;)y~r-oxiues, oar~onaces an~ bicar-bonates of the
me~als of ~roups I al)d II, as well as diborates ~e.g.:
i~a2B4G73; a~l o; them being watet-soluble.
Pre~erred cornpound are those containing Mg, Na, Ca;
parciculariy pr~ferred are non-toxicant compounds, such as
maynes-ium ans sodium ox-ide~, carbonates and bicarbonates,
and calciurn and magnesium hydroxides.
The hydrophobic organic solvent used in the
microemulsion accordirlg to the present invention has a
boiling poin~ comprised witnin the range of from O'C to
16ûC, pre;erarly comprised within the range of from ~O'C to
1 û ~,
Non-limiting examples of solvents are cyclohexane, n-heptane, n-hexane,
isooctane~ The preferred solvent is heptane.
The surfactar)t pr-esent in the microemulsion according
10 trle present invention is used in order to stabilize the
small dispersed water droplets, reduc;ng the interfacial
~ension o; the sy~tem.
Examples of non-ionic surfactants are polyethoxylated
long-chain aliphatic alcohols, in particular
CH3~(CH2)n-CH20~(CH2CH20)m-CH2CH2OH
in which n = l-~û, and m = 1-1ûû; the fatty acids monoesters
wi~h polyoxyethylene, in particular sorbitol monostearate
(monopalmitate, and so forth); ethoxylated nonyl-phenols, ;n
particular
1n3-(c~l2 )8-C6 H4~0~(CH2u;12G)n~H
irl w;lich n = 1-lûG.
Examp1es of ion ic surfactants are A:)T (sodium
dioccy1su1fosurcinate) and SGS (sodium laurylsulfate).
When a nor1-ionic surfactant is used, the use of only
one sur-fac:tant is enough Gn the contrary, when a ionic
surfactant is used, it is sometimes necessary to employ a co-surfactant which
decreases the density of surface charge generated by the ionic surfactant,
reaching the interface and thus decreasing the interfacial tension. In that way,
the co-surfactant makes it possible to achieve a dispersion of small water
droplets. An example of Such a co-surfactant iS a linear-chain aliphatic alcohol
with 3-16 carbon atoms, in particular n-butanol, n-pentanol, n-hexanol.
The microemu1sion according to the present invention
obtained in tna~, way is suitab1e for the treatment of acidic
paper in or der- to decrease the acidity thereof, and
considerabiy s10w down its degradation over time and
a1teration of i ~s mechanical proper-ties.
In another of its aspects, the present invention provides a process for the
treatment of paper products, characterized in that the products are
impregnated by di,uping into the above disclosed microemulsion, and the
surfactant is subsequently removed by washing with solvent and the products
are dried.
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;r~ ~he process accordillg ro cr)e ~resent inven~iorl -che
irrl~re91~a~iOrl OT ~aper wi~h rhe emulsion -is carried out at
roorl) ~errlperature (2~ C). Trhe weiyh~ ratio of mirroemulsion
to pa~er is comprised within the range of frorn 1:1 to 50:1.
The washirly of ~he impr-egnated paper is carried out
wi~h a solvent, for example with an apolar solvent such as
n-hep~ane, or an alcor)ol such as e~hanol.
Tne resul~iny ~reated paper- is dr-ierJ at a temperature
co(llprised wicr~in cr-he range of fr-om O-C to ~G-C preferably
comprised wi~hin the range of frorn 25C to 6~ C.
The evaluacion of the treatment is carried out by means
OT rneasurement OT pH value and of alkaline reserve of paper.
~ ccording to the preferred process the WjO
rnicroemul~ion is prepared by starting from an aqueous
soluiion con~a;ning salts of alkali metals or alkaline earth
metals, a hydrophobic solvent and a surfactant. The acidic
paper is impregnated by being dipped into this microemulsion
a~ room terrlperature. The ratio of microemulsion to paper, by
weight, is comprised within the range of from 2:1 to 20:1.
After the impregnation paper ;s washed with the
solvent and then is oven dried at the temperature of ~O C.
The values obtained for the alkaline reserve and for the pH
value of paper demonstrate that the process according to the
present invention provides a high de-acidification rate.
Therefore, the process according to the present
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invention makes it possible to treat in bulk paper products, suCh as books
(without that they have to be disassembled), drawings, paintings on paper,
paintings, documents, and so forth; the fast deposition of alkalifier agents on
paper fibres, or fast deacidification of paper; and the removal of soil from
paper.
, he process acc;ording to the present, invention is
sui~aL)ie Tor deacidifying cellulose-based paper, as well as
,~ui,o-~;on~aining paper.
Tbe process ~ccording to the present invention is
simF~le and c:hea~, because it does not require special
eclu i pmen t ~ and i s env i ronmental 1 y compati bl e, because the
reac:tants used c:an be recycled wi thout releasing eco-toxic
~uL~ance~; into the env i ronment.
In erder to better understand the present invention,
arld to practice i t, some ; 1 lustrat;ve, non-limiting
examples are reported in the following.
The pH vaiue and the reflectance within the blue range
[~ (3~) j have been determined according to the methods as
described by Gavid N.-S. Hon, Historic Textile and Paper
Materi~ls II; Chap~ter 2, page 24, American Chemical Society,
1 369 .
Exam~l e
A water-in-oil (W~O) microemulsion was prepared by
s i mpl y mi x i ng the fol 1 ow i ng components:
~ Q ~ 3 - ~ ~
I / 70 (.)T il~) I,dl~
1~ OT so~iurTI dioc T y 1 SU 1 T oSur_c i nate, ~nd
a7r OT an ~4ueous solution OT s~ldium bicarbonate at 5% by
weiyh~.
A sheec OT pure cellulose Whatlnarl paper with pH 5.7 was
imllletseri in cnis microemulxioll. Tne paper was soahed for one
hour at roorrl temper-a~ure (25 C~. The ratio of microemulsion
t~ paper, uy weiyhc, was 5:1.
~ o treated paper was subsequently washed with ethanol,
arld then was dr-ieo inside arl air-circulation oven at 50'C
for 3U rminutes
The fo71Owirlg charar_~eristics OT paper were determined:
p~ = 10.0; depusiced alkaline reserve 0.1û~ (as expressed as
percent CaC03 content, based on paper weight).
Exam~le 2
A water-in-oil ~W/0) microemulsion was prepared by
simply rnixing tne following components:
80,u~ by weight OT heptane,
11,5~ by weight of sodium dioctylsulfosuccinate, and
8,5~ by weight of an aqueous solution of magnesium
bicarbonate at 4% by weight.
A sheet of pure cellulose Whatman paper with pH 5.7 was
immersed in this microemulsion. The paper was soahed for one
hour at room temperature (25 C). The ratio of microemulsion
to paper, by weight, was 5:1.
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The so-treated paper wac subsequently washed with ethanol and then
was dried inside an air-circulation oven at 50DC for 30 minutes.
The fo71Owiny crlar~c~eristics of paper were determined:
pH = 5 i; deposileu alkalirle reserve 0.15~ (as expressed as
per cer~r, Ca~03 con~en~, based on paper weight).
Exam,ole 3
wa~er-irl-oil (WjOj microemulsion was prepared by
~ilnply mi~iny ~he followiny components:
~û ~ or heptarle,
i 1, 5~ OT sod i um dioc:tylsu7fosuccinate, and
OT an aqueous so7utiorl of magnesium bicarbonate at 4%
by wei ght
h pu7p-corlrairlirlg paper sheet, visibly yellowed and
naviny a pH value of 5.1, was dipped in this microemulsion.
The paper was soaked for one hour at room temperature
~5'C) Tne ratio of microemulsion to paper, by weight, was
5 1
So ~r-ea~ed ~aper was subse4uently washed with ethanol
arld then was dried inside an air-circulat;on oven at 50-C
Tor 30 minutes.
The following character;stics of paper were determined:
pH = a.6; reflectance within the blue range [Z (~)] 57.
The resulting paper was exposed to those condit;ons
whir_h ar-e known to cause an accelerated paper ageing.
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InereTore~ ~a~er was ke~ stored inside an oven at 90 C with
a rela~ive humidity of 5G~.
Under such conditions, during a one week storage, paper
undergoes a degradation rate which corresponds to 147-420
years of natùral ageing.
The resùlts obtained are reported in follow;ng Table 1.
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~'3 ~
. .
o
~, "- C~l ~ ~ t
~ ~ ~ = ~ C , =,~,
o~ ~ , ,, ~
~,
U~
g
L _ "
O ~_
- 15 ~ .r ~ ~
Exan)Dle ~
A warer-in-oil (WjO) microemulsion was prepared by
simply mixing the following comp~nents:
aG ~ of heptane,
11,5% of sodium dioc~ylsulfosucc;nate, and
8,~ of an aqueous solution of magnesium hydrogen
carbona~e a~ 4X by weight
A book (tied paper sheets having a pH value of 5.1) was
dipped into this microemuls;on. The book was soaked for one
hour at room temperature (25'C). The ratio of microemulsion
to book, by weight, was 2:1.
The so treated book was subsequently washed with
etharlol and then was air-dried, at room temperature.
The treated book had a pH value of 7.2.
ExamDle 5
A water-in-oil (W/0) microemulsion was prepared by
simply mixing the following components:
~,5X of heptane,
22,5~ of LIALET 125j2(~) (a mixture of diethoxylated Ct20H
and C1 5 OH),
lG,0~ of an aqueous solution of magnesium bicarbonate at 4X
by weight.
A sheet of pure cellulose Whatman paper with pH ~.7 was
immersed in this microemulsion. The paper was soaked for one
hour at room temperature ~25'C). The ratio of microemulsion
-- 16 --
r,'~
? r , L) y w ~ i ~ i l i,, ~ ,, ~ --, i ,
r~ p~p~?r was subsequentlY waerleri with ethan~l
erl wa~, ~ir ie~i in~irie ~n air-r_iroulaibion oven ~ û'~,
r .^,U Irl i rl~",~!j,
;oliowin~ or~ar-ar~,ler isi,iC,s or ,oaper were de~ermined:
,uii = ~ . r~; rie~ s i ~ed aiha7 ir~e r~ser ve ~1.11% ~ax exl~ressed as
r ~ r ~ , u3 (~ o r ~ L~ ~ r~ r~ O r ~ ) r-~ r W ~3 i 9 rl t ) .
