[NHCOLL-L:4295] Fw: re: Nalgene paper and Tyvek

Thu Apr 9 10:52:27 EDT 2009

I have been following the Nalgene and Tyvek label discussion with interest
and would like to offer the following comments and observations that may
help to clear up some misconceptions.

PET and polyolefin are not the same thing.

In conservation, the term "polyester" usually refers to poly(ethylene
terephthalate), PET, which can be considered as the condensation polymer of
terephthalic acid and ethylene glycol (although it is not necessarily made
from these compounds). This polymer is used in conservation in sheets like
Mylar, Melinex, and Hostaphan, fibres like Dacron and Terylene, and
spun-bonded or non-woven textiles like Reemay and Hollytex. Pop bottles are
made of PET. A good discussion of poly(ethylene terephthalate) is given at
http://en.wikipedia.org/wiki/Polyethylene_terephthalate .

Polyolefin is a general name for the class of polymers made from olefins,
or alkenes, which are hydrocarbons with double bonds, such as ethylene
(ethane), propylene (propene), butylene (butane), hexane, octane, etc. If a
single olefin monomer is used to make the polymer it tends to be name after
that monomer, such as polyethylene or polypropylene. If more than one type
of monomer, and especially if the higher molecular weight monomers are
used, the term polyolefin is often used. Polyolefin products commonly used
in conservation include Coroplast, Tyvek, Ethafoam, Volara, Plastazote,
Tupperware and similar food storage containers, etc.

Tyvek is fully described at www.tyvek.com . The Product Handbook for DuPont
Tyvek at
http://www2.dupont.com/Tyvek/en_US/assets/downloads/tyvek_handbook.pdf and
DuPont Tyvek User's Guide at
http://www2.dupont.com/Tyvek_Graphics/en_US/assets/downloads/DuPont_Tyvek_Users_Guide.pdf
 are highly recommended reading, with much discussion about printing. All
Tyvek is spun-bonded polyolefin, specifically high density polyethylene,
with no binding agents.  There are two basic forms of Tyvek.  Type 10 is a
hard paper-like material, which is the type most suited for labels. Types
14 and 16 are soft textile-like materials and are not suitable for most
labels. I do not think there is much difference in the chemical composition
of the fibres that make up these different types, but rather in the thermal
and mechanical treatment that the web receives after it has been formed
during the initial filament spinning process. Tyvek Brillion is a special
Tyvek style, made by a method that produces thinner fibres, and which is
calendered at higher temperatures and pressures to a yield a smoother
product especially suited for high quality, high resolution printing.

PET is more resistant that polyolefin to damage by UV radiation. For
instance, PET is one of the most UV resistant fibres used to make
sailcloth. However, long exposure will cause damage. In contrast,
polyolefin is quickly damaged by UV radiation.  The Product Handbook for
Tyvekstates: "Physical properties of spunbonded olefin are degraded with
extended exposure to direct sunlight (ultraviolet rays), although at least
one to three months of useful outdoor life can be expected in many
applications. UV resistance can be improved with opaque coatings. Styles of
spunbonded olefin containing UV inhibitors are available for applications
requiring higher UV resistance." Degradation of maps on walls and house
wrap that may have been exposed for months to sunlight is probably a
manifestation of UV damage, most likely by photo-oxidation.

Polyolefins are hydrocarbon polymers. They contain no ester groups that are
susceptible to hydrolysis. As its name indicates, PET, or polyester,
contains ester groups that are susceptible to hydrolysis. Fortunately for
water and pop bottle makers, and conservation, this occurs only at elevated
temperatures, near the softening point of the plastic. PET must be dried
before thermal processing to prevent hydrolysis at processing temperatures,
but hydrolysis is not a problem at room temperature.

PET has greater resistance to thermal oxidation than polyolefin. However,
at room temperature it is unlikely that much thermal oxidation occurs in
polyolefins.

There is considerable evidence that both PET and polyolefins have
longevities of decades in good museum conditions.

Decades of study on PET, especially in connection with photograph film base
and archival storage products indicate that PET remains unchanged for
decades (some say centuries).

In 1975, W.F. van Altena published a paper entitled "Envelopes for the
Archival Storage of Processed Astronomical Photographs" in the American
Astronomical Society Photo Bulletin, V. 1, p. 18-19, 1975, in which he
described experiments using Tyvek envelopes to store astronomical
photographic plates that began in 1971 and included tests that consisted of
keeping processed colour film in contact with Tyvek sheets for 14 and 28
days at 60 deg C and 70 percent RH.  These tests showed no effect of the
Tyvek on the dye stability.  In January 2008 I corresponded with van Altena
to ask him how the envelopes were holding up now.  His response was: "I
have just checked the old Tyvek envelopes that I started using here at Yale
when I moved in 1974 (The envelopes probably date from around 1979.) and
found no evidence of degradation.  In the old paper envelopes that I
investigated (early to mid-1900's envelopes) I often found a residue on the
glass side that was transferred from the paper as well as the more obvious
transfer of glue from the seams onto the emulsion or glass.  Even when the
emulsion was placed opposite to the seam, some transfer was noted that had
passed through the adjacent envelope.  In the case of the Tyvek, I see no
evidence of outgassing from the Tyvek or glue.  The latter was always of
great concern in our study of using Tyvek, since heat bonding was not
possible with Tyvek."

I have been saving Tyvek mailing envelopes for decades.  I have 30 year old
Tyvek envelopes that show no apparent discoloration or brittleness. Stamps,
postage meter labels, closure flap adhesives, seam adhesives, and printed
inscriptions appear to be unchanged. I have maps printed on Tyvek that are
more than 15 years old that have been on canoe trips and were surely
exposed to some sun and water. These show no apparent changes, aside from
wear due to use. These observations indicate longevity of more than 30
years for printed Tyvek at ambient conditions.

At room temperature, in good museum lighting with no UV, and at moderate RH
(30-50%) both PET and polyolefin are chemically stable, and have proven
longevity of at least 30 years.

All types of Tyvek can have various surface treatments such as untreated,
corona discharge to promote adhesion of inks and adhesive, antistatic
agents to dissipate electrical charge, and clay coatings to improve
printability, on one or both sides. Tyvek Type 10 has a rough and a smooth
side. For labels, printing on the correct side of a suitable grade with
suitable surface treatments is required. The Handbook and User 's Guide
provide guidance.

R. Scott Williams
Senior Conservation Scientist (Chemist)
Conservation Research Division
Canadian Conservation Institute
1030 Innes Road
Ottawa, Ontario, Canada K1A 0M5
tel: (613) 998-3721
fax: (613) 998-4721
email: scott_williams at pch.gc.ca

Visit the CCI Web sites at www.cci-icc.gc.ca and www.preservation.gc.ca