Fiber Processing & Paper Performance
FS-FPL-4710
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Laboratory Facility |
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Vacuum Compression Tester |
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Imaging Systems |
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Semiautomatic Handsheet |
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Mold Flotation Cell |
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JunYong Zhu, Ph.D.
Project Leader
Phone: (608) 231-9520
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Pressure Sensitive Adhesives:
Recycling Evaluation of
New-Generation
Environmentally Benign Pressure Sensitive Adhesives
| Abstract | Introduction | Discussion | Conclusion | References |
Abstract
As a result of a United States Postal Service (USPS) initiative,
a work team was formed consisting of representatives from USPS,
Forest Products Laboratory (FPL), Specialized Technology Resources,
Inc. (STR), and industry representatives, including papermakers,
paper recyclers, paper collectors, equipment manufacturers, paper
users, adhesive manufacturers, and chemical suppliers. The objective
of the work team was to develop new and innovative solutions to
problems associated with recycling paper containing pressure sensitive
adhesives (PSAs). Based on criteria developed by the work team,
the adhesive industry formulated new PSAs that are largely removed
by screening stages of recycling processes. Protocols were also
developed to evaluate newly formulated adhesives. This paper describes
a pilot-scale recycling sequence used to assess removal of contaminants
from feed stocks containing PSAs. The process sequence involves
high consistency pulping, pressure screening, forward and reverse
cleaning, and washing and flotation deinking. Fourteen newly formulated
adhesives have been evaluated using this pilot-scale protocol.
Introduction
Removing contaminants from recovered paper pulps is one of the
biggest environmental challenges facing the paper industry. It is
also one of the major technical barriers to paper recycling. Despite
advances made during the past few years, contaminants from adhesives
cause major problems during both recycling of paper and subsequent
papermaking. Stickies are undesirable recovered paper components
that come from pitch, ink, plastic films, converting aids, paper
coating, and adhesives. These contaminants are called stickies by
papermakers, because they stick to paper machine felts and wires
and cause many operating problems. A large fraction of the stickies
is PSAs, which are found in products such as labels, tapes, and
some postal materials.
Since the USPS currently purchases about 12% of the domestic PSA
production, the USPS can play a significant role in guiding adhesive
development. The main objective of the USPS's program for environmentally
benign PSAs is to develop postage stamp adhesives that are environmentally
benign. For the purposes of this project, environmentally benign
PSA is defined as an adhesive that places no additional burden on
recycled paper mills. Additionally, the adhesives have to fulfill
all other USPS specifications, shelf life, permanence, and philatelic.
The goal is to develop PSA stamp products that can be successfully
recycled into paper products in a typical recycling facility, particularly
those plants supplying pulp for printing and fine grades of paper.
This paper describes some of the program's major issues, team efforts,
and final products.
Top of Page Discussion
Despite the fact that PSA stamps are very popular with the general
public, there are some serious concerns regarding their environmental
impact. To address these concerns, the USPS in conjunction with
FPL, STR, and paper industry representatives, organized several
national PSA meetings to incorporate the input of the adhesive manufacturing
industry and the paper manufacturing industry (1,2,3). The issues
raised and discussed included: problem definition, communication,
education, source quality control, recyclability standards for PSAs,
paper industry perspective, end-product specifications, and the
role of technology. The meetings concluded that problems caused
by stickies are best resolved through combined efforts of the adhesive
industry, the paper industry, and the process equipment manufacturers.
Keeping in mind the criteria set by the paper industry, the adhesive
industry is striving to formulate new PSAs that are mostly removable
in the screening step. The work team met several times to discuss
and decide on the image analysis and pilot plant testing protocols
to use to evaluate the newly produced adhesives on a small scale.
The team agreed that there is a need for a standard method for testing,
more information on the removal efficiencies during recycling unit
operations, and a reasonable method that combines pilot testing
and image analysis.
As a result of all these combined efforts, a pilot-scale
separation sequence was developed to assess the removal of adhesives
from the
feed stock containing PSAs. This pilot-testing protocol simulating
a typical recycling operation included high consistency pulping,
coarse and fine pressure screening, forward and reverse cleaning,
and washing and flotation deinking. Modified TAPPI standard dirt
counts were developed, and handsheets were made from pulp samples
after each unit operation and on paper samples from the paper
machine runs. The protocols simulating typical recycling operations
and
using preconsumer, postconsumer, and control stocks were further
refined to reflect ptimum operating conditions such as temperature,
consistency, screen size, repulping energy, and chemical additives.
Current efforts involve laboratory testing of commercially produced
PSAs, stamp print and finish trials, mill-scale recycling trials,
and development of the final specification and approved product
list for PSA stamp production. In addition to being recyclable,
the final specification includes stringent USPS performance requirements.
These stamp requirements include permanent adhesion to envelop substrates
and ability to withstand long-term aging (archive ability).
Results of this work team were presented by all
participants at the 1998 TAPPI Recycling Symposium cosponsored by the
USPS and FPL
and held in New Orleans on March 8- 12, 1998 (4). In addition,
invited presentations were given at the 1998 PIRA Deinking Conference
in
England (5) and the PTS/CTP Deinking Symposium in Germany (6).
Plans are underway to present the final results of this project at the
TAPPI Recycling Symposium to be held in Washington, DC, March
5-
8, 2000.
Top of
Page Conclusions
Although the USPS’s role in initiating this
program was essential, the cooperative partnership stemming from this
research
program
has resulted in progress towards resolving environmental problems
caused by PSAs. Involving all parties in defining and solving
this environmental problem has proven to be effective. Specific
accomplishments of this cooperation include new testing protocols for
the recyclability
of PSAs and a database of information on the newly formed
PSAs. Although the initial effort of this work were directed at modifying
adhesives for stamps, it is anticipated that the results and
recommendations
resulting from this research program will be applied to labels,
stickers, and a wide range of similar PSA products. References
- Peng, et
al. Proceedings of the USPS/Springborn Joint Conference
Covering Environmentally Benign PSA for
Postal Applications, Windsor,
CT, 14 February 1995. U.S. Postal Service (1995).
- Peng,
et al. Proceedings of the USPS/AFPA Joint Conference
on PSA Issues, Washington, DC, 25 June 1996, U.S.
Postal Service
(1996).
- Peng, et al. Proceedings of
the Environmentally Benign PSAs for Postal Applications,
Washington, DC,
7-9 July
1997, U.S. Postal
Service (1997).
- AbuBakr, Said et al. Proceedings
of the 1998 TAPPI/USPS/FPL Recycling Symposium, New
Orleans,
9-11 March 1998, Tappi
Press (1998).
- AbuBakr, Said et al. Proceedings
of the 5th International Recycling Technology Conference,
Brighton,
England,
9-10 February 1998,
PIRA (1998).
- AbuBakr, Said et al. Proceedings
of the 1998 PTS/CTP Deinking Symposium, Munich, Germany,
6-8 May 1998,
PTS/CTP (1998).
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