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<div class="moz-cite-prefix">Dear all,<br>
<br>
sorry for picking this discussion up again (after returning from
vacation).<br>
<br>
It may not only be the chemical & physical composition of the
liner that may cause or accelerate its deterioration, but also
additives and/or denaturing agents added to the ethanol which may
speed up degradation of plastics. I am not sure if Canadian
Museums have to use denatured or undenatured ethanol. In Europe a
large variety of denaturing agents has been used during the last
century, leading to quite complex chemical mixtures after topping
up evaporation losses for decades. As a matter of fact, this tends
to give single lots a unique chemical history. Destruction might
even speed up if aggressive additives do have higher evaporation
rates compared to ethanol (resulting in a very reactive, highly
concentrated small gas atmosphere between fluid surface &
lid). <br>
<br>
"Cracking of [some] plastics" might also be expedited from
degradation products of/or residual formaldehyde escaping from
formalin fixed specimens.<br>
<br>
As far as I know, the colleagues in Bern/Switzerland have been
testing Teflon liners designed for (standardised metal) twist-off
lids with promising results, but I do not have first-hand
information on this.<br>
<br>
All the best<br>
Dirk <br>
<br>
Am 01.08.2012 19:33, schrieb Paul Callomon:<br>
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<p class="MsoNormal">Colleagues,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Realizing the possible implications for us
all of age-related failure of jar lid liners, I have been
doing some survey work. The results are encouraging. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph"
style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="mso-list:Ignore">-<span style="font:7.0pt "Times
New Roman""> </span></span><!--[endif]-->The
supplier of the liners, O. Berk (KOLS Containers in those
days) have confirmed that the liner in question is a generic
version of the Tekniplex F217 liner that differs from the
brand-name version only in the blowing agent that is used to
foam the center core. The outer skins are solid low-density
polyethylene, and the center is foamed LDPE. <o:p></o:p></p>
<p class="MsoListParagraph"
style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="mso-list:Ignore">-<span style="font:7.0pt "Times
New Roman""> </span></span><!--[endif]-->I
retrieved and tested several other jars using the same lid
that were put into service in the same or following year
(2000-01). The lids thus came either from the same batch as
the failed one, or from another batch that was purchased
shortly after. I carried out a simple visual examination
followed by a pliability test. For the latter, I lifted the
edge of the liner (it is glued to the inside of the lid) in
two places using a dental hook and folded a flap over until it
touched the surface of the liner (folded double). When it had
returned, I inspected the surface. The material showed some
wrinkling from this treatment, as is normal, but no cracking
or crazing. This is the same thing that happens with a brand
new liner, and although the wrinkling remains to a certain
extent, this does not seem to compromise sealing.<o:p></o:p></p>
<p class="MsoListParagraph"
style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="mso-list:Ignore">-<span style="font:7.0pt "Times
New Roman""> </span></span><!--[endif]-->By
contrast, the failed liner snapped when folded over, and its
surface is covered with a combination of fractal (branching)
crazing as well as the cell-like crazing one sees in old
ceramic glazes. The material has thus clearly undergone a
major chemical change, and a colleague has generously offered
to run tests to try and diagnose this. <o:p></o:p></p>
<p class="MsoNormal" style="margin-left:18.0pt"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:18.0pt">In conclusion,
it seems that this might have been a single incident. The next
step is to trace the history of the contents (13 separate
specimen lots in glass tubes) and see what treatments were
used on them that might have caused this problem. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif"">Paul Callomon<o:p></o:p></span></b></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
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Malacology, Invertebrate Paleontology and General
Invertebrates<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-top:4.0pt"><span
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Academy of Natural Sciences of Drexel University<o:p></o:p></span></p>
<p class="MsoNormal"><span
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<p class="MsoNormal"><span
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