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Náhrada xylénu
Termín xylen nebo xylol obvykle označuje směs tří izomerů aromatického uhlovodíku (dimethylbenzenu) používaného jako rozpouštědlo v tiskařství, lakýrnictví a v gumárenském a kožedělném průmyslu. Je to čirá, bezbarvá kapalina nasládlého zápachu, hořlavá. Obvykle se získává v rámci rafinace ropy. Konkrétně se získává např. z reformátu (produkt reformování benzínů), jako vedlejší produkt při alkylaci aromátů, při transalkylaci (též disproporcionaci) toluenu. Chemická rovnováha mezi izomery je příznivě nastavena ve prospěch izomeru meta, který je nejméně žádaný. Proto bývá v rafinérsko-petrochemických komplexech instalován proces izomerace xylenů. Podobně jako jiná rozpouštědla je i xylen zneužíván jako inhalační droga.
Date: 29 Jan 2012
From: Monona Rossol <actsnyc [at] cs__com>
Subject: Alternative to xyleneRaymond A. Spiteri <raymond.a.spiteri [at] gov__mt> writews
>We are seeking a less hazardous alternative to xylene to be used in
>solvent mixtures and for dissolving acrylic resins like Paraloid B72
>for eventual use in conservation treatments. Can anyone suggest, or
>has used, a viable alternative. Has anyone used 'Clarify' as an
>alternative to xylene, and if so, is it a viable alternative.Google doesn't come up with any brand name solvent called Clarify.
Must be very local and you'll need to identify the actual chemicals.
On the theory Clarify might be one of the "natural" solvents which
sometimes function as aromatics, I've addressed them here, too.It seems you need a light aromatic solvent. So I looked at all the
usual suspects.TLV-TWA MAK-TWA
——- ——-Benzene 0.5ppm 3A—-*
Toluene (methyl benzene) 20 ppm 50 ppm
Xylene (di methyl benzene mixed isomers) 100 ppm 100 ppm
Trimethyl benzene isomers 25 ppm 20 ppm
Ethyl benzene 20 ppm 3A—-*
Turpentine 20 ppm Sh**
Citrus oil (d-limonene) 20 ppm 3A—-** The German's don't set limits for germ cell mutagens that can
cause damage the embryo (or for human carcinogens). They think that
it is immoral to set a limit which amounts to deciding how many
fetuses and/or workers it is acceptable to kill.** The Germans also don't set limits for strong sensitizers.
So you can see xylene is universally thought to be the least toxic
of the light aromatics and you are probably stuck with it. Even the
aliphatic hydrocarbons such as mineral spirits are all now (as of
2011) in the range of 100 ppm. So you can't really do better with
any solvent I know about.Monona Rossol, M.S., M.F.A.
industrial hygienist
Arts, Crafts &Theater Safety, Inc.
181 Thompson St., #23
New York NY 10012-2586
212/777-0062——————————
Date: 12 Feb 2012
From: John Burke <jb [at] museumca__org>
Subject: Alternative to xyleneSmadar Gabrieli <smadar.gabrieli [at] uwa__edu__au> writes
>Raymond A. Spiteri <raymond.a.spiteri [at] gov__mt> writews
>
>>We are seeking a less hazardous alternative to xylene to be used in
>>solvent mixtures and for dissolving acrylic resins like Paraloid B72
>>for eventual use in conservation treatments. Can anyone suggest, or
>>has used, a viable alternative. Has anyone used 'Clarify' as an
>>alternative to xylene, and if so, is it a viable alternative.
>
>I don't know of a substitute to xylene for all applications, but
>since you specify B72, it is miscible in Acetone and in Ethanol, or
>a mixture of the two. So is B67. Change the proportion according to
>the necessary working time. When making decision about which one to
>use, check also for change of colour – in different situations one
>or the other may cause change, while the other doesn't.I agree that acetone and/or ethanol might be reasonable alternatives
to xylene for B-72, at least from a health perspective if properties
and effects are acceptable. Be careful with commercial solvent
substitutes though: most replacements for aromatics, such as
esters/cycloalkanes, are more driven by VOC regulations than
exposure limits (though I see a number of histology solvent
replacements online, q.v.). Check the MSDS carefully, and compare
threshold limit values (TLVs) as a start.——————————
Date: 13 Feb 2012
From: Simon Moore <couteaufin [at] aol__com>
Subject: Alternative to xyleneRaymond A. Spiteri <raymond.a.spiteri [at] gov__mt> writews
>We are seeking a less hazardous alternative to xylene to be used in
>solvent mixtures and for dissolving acrylic resins like Paraloid B72
>for eventual use in conservation treatments. …I too am looking for an alternative for xylene but to loosen
coverslips on archival microslides mounted with Canada Balsam,
Euparal and the like and, on which, xylene works very well. If
there is a more user-friendly alternative I would be pleased to hear
of it. I have had Cumene suggested, since the molecule is close in
structure, but have had no experience with this.Simon Moore MIScT, FLS, ACR,
Conservator of Natural Science——————————
Date: 13 Feb 2012
From: Greg D. Smith <gdsmith [at] imamuseum__org>
Subject: Alternative to xyleneSmadar Gabrieli <smadar.gabrieli [at] uwa__edu__au> writes
>Raymond A. Spiteri <raymond.a.spiteri [at] gov__mt> writews
>
>>We are seeking a less hazardous alternative to xylene to be used in
>>solvent mixtures and for dissolving acrylic resins like Paraloid B72
>>for eventual use in conservation treatments. Can anyone suggest, or
>>has used, a viable alternative. Has anyone used 'Clarify' as an
>>alternative to xylene, and if so, is it a viable alternative.
>
>I don't know of a substitute to xylene for all applications, but
>since you specify B72, it is miscible in Acetone and in Ethanol, or
>a mixture of the two. So is B67. Change the proportion according to
>the necessary working time. When making decision about which one to
>use, check also for change of colour – in different situations one
>or the other may cause change, while the other doesn't.It is important to note that the glass transition temperature (Tg)
of solvent cast B-72 films depends heavily on the solvent used. The
recent suggestion to switch to ethanol or acetone from xylene could
lead to large changes in the dry film Tg and hence mechanical
properties like strength, toughness, and elasticity. The Tg
reported by Hansen et al. for B-72 in acetone is 42C while toluene
gave a film with Tg at 31C. Measurements in my lab for young films
(150 days old and less than 1.5% retained solvent) of 4% w/v B-72
have given Tg values at 46C for acetone, 33C for toluene, and 18C
for xylene. We are waiting to see if the xylene film, which
currently has retained solvent identical to the toluene film,
eventually achieves a similar Tg value over time as one would expect
from such similar solvents. The current discrepancy may have to do
with the larger radius of xylene and hence greater plasticization
for equal amounts of solvent. In our experience ethanol (at least
pure, undenatured ethanol) is a very poor solvent for B72 (at least
the old formulation of B-72) forming a thick mucus at even 4% w/v
concentration that could only be dispersed in the solvent with
vigorous shaking.Gregory Dale Smith, Ph.D.
Otto N. Frenzel III Senior Conservation Scientist
Indianapolis Museum of Art
4000 Michigan Road
Indianapolis, IN 46208-3326
317-923-1331 x154
Fax: 317-931-1978——————————
Date: 13 Feb 2012
From: Alan Phenix <aphenix [at] getty__edu>
Subject: Alternative to xyleneSmadar Gabrieli <smadar.gabrieli [at] uwa__edu__au> writes
>Raymond A. Spiteri <raymond.a.spiteri [at] gov__mt> writews
>
>>We are seeking a less hazardous alternative to xylene to be used in
>>solvent mixtures and for dissolving acrylic resins like Paraloid B72
>>for eventual use in conservation treatments. Can anyone suggest, or
>>has used, a viable alternative. Has anyone used 'Clarify' as an
>>alternative to xylene, and if so, is it a viable alternative.
>
>I don't know of a substitute to xylene for all applications, but
>since you specify B72, it is miscible in Acetone and in Ethanol, or
>a mixture of the two. So is B67. Change the proportion according to
>the necessary working time. When making decision about which one to
>use, check also for change of colour – in different situations one
>or the other may cause change, while the other doesn't.To pick up on the posts about solvents for Paraloid B72, there
are–of course–quite a lot of different solvents for this resin.
However, solvent selection depends on a whole host of factors:
chemical and physical properties, health hazards, environmental
effects, and many more; not to forget what might be safe to use with
any given object and all kinds of application-related factors. It
all depends on what you are trying to do with the resin. For sure,
acetone will dissolve B72 quite well (ethanol less so), but it
evaporates very fast. While that might (just) be OK for B72 used as
an adhesive, that probably wouldn't be OK for most coating
applications (ie. lacquer or varnish), or penetrating consolidant.In the context of finding safer alternatives to xylene, for use with
B72 as a retouching medium for easel paintings, over 20 years ago I
suggested the glycol ether 1-methoxypropan-2-ol CAS #107-98-2) as
one possibility. This cannot be regarded as harmless, with European
occupational exposure limits (WELs in the UK) of 100ppm/ 375 mg per
m3; but it is appreciably less hazardous than xylene (UK WEL 50ppm/
220 mg per m3). And 1-methoxypropan-2-ol is a doubly-functional
oxygenated solvent, which might mean that it is too 'active' for use
in certain applications on certain objects on account of risk to the
original material.There are, it seems, quite a few solvent products out there that
offer themselves as 'xylene substitutes'; these are often intended
for use in fields such as histology, where xylene has traditionally
been used for solubilizing lipids. I don't know anything about the
product 'Clarify', but in the United States I am aware of a couple
of 'xylene substitute' solvents offered by CBG Technologies in Ohio:
Formula 83 and Formula 78H. (Formula 78H, which has the higher
boiling point is marketed actually as a substitute for higher
boiling aromatic solvents of the high-flash naphtha type, eg.
Shellsol A100, etc.). I'm sure there are probably quite a few
other products of this type out there. Basically, these solvents are
naphthenic (ie., cycloparaffinic) hydrocarbon blends. Shell North
America no longer offers any products of this type: its solvents
Cypar 7 and Cypar9 were discontinued some years ago. In Europe,
there is a potentially useful similar product from ExxonMobil in the
form of Nappar 10, but how one might get hold of small quantities of
that, I don't know.Naphthenics are composed of saturated cyclic aliphatic hydrocarbon
compounds, not aromatic hydrocarbons, which accounts for their lower
'harmfulness'; but they are less polar/polarizable than aromatics,
so have lower solvent power. While they have the greatest solvent
power of the wider group of aliphatic hydrocarbons (which includes
also n-paraffinic and iso-paraffinic types) such naphthenic solvents
are not active enough in themselves to dissolve Paraloid B72 (I have
in front of me some in B72 in a jar of 78H, and it has not
dissolved.). In principle, though, it is possible to create solvent
mixtures of a non-polar solvent like these naphthenic hydrocarbons
(or any type of mineral spirits) and an oxygenated solvent (such as
one of the glycol ethers or ether esters) that would have sufficient
solvent power to dissolve B72. However, I would not yet propose
trying that option until the research is done; one key factor is
balancing the evaporation rates of the components so that relatively
constant solvent composition is maintained throughout drying, in
order to prevent the resin precipitating out prematurely. We are
presently in discussions with Dow Coatings Materials, makers of the
resin, on the specific topic of alternative solvents (and blends)
for Paraloid B72.Alan Phenix
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