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D.G. Bailey, W. J. Hopkins, H. H. Taylor **, and F. M. Filachione
Eastern Regional Research Center Philadelphia, Pennsylvania 19118 AND R.G. Koeppen S.B. Foot Tanning Company Red Wing, Minnesota 55066 |
The hides treated by drumming produced leather equal or superior in
quality to the controls. Use of the more concentrated solution applied by
spraying produced leather with unacceptably loose break
The result demonstrate that a sulfite and acetic acid preservation can be
adapted to current leather processing methods under tannery conditions to
produce commercial quality side upper leather. This method provides the tanner
with an alternative to fresh or salt cured hides.
Effluent disposal in many localities. The elimination of the cost of salt and the
labor needed to apply it would result in additional savings.
A variety of methods have been proposed to attain short-term nonsalt
preservation of raw hides. Smykel and Juva (1) have proposed a chilling
procedure for a two-to three-day preservation. Hughes (2) reported a temporary
preservation of hides with boric acid, and Cooper and Galloway (3)
demonstrated short-term preservation using a combination of chlorite and zinc.
A method reported initially several years ago and recently described in detail by
Buechler (4) involves acetone dehydration of fresh hides. Our laboratory (5) has
published methods on the use of polyhydric alcohols for dehydration and
preservation of hides. Each of these methods has been shown to provide
effective preservation, but each appears to have certain limitations due either to
cost, the need for special equipment, or loss in quality of the resulting leather.
Previous work from our laboratory (6,7) demonstrated that the sulfite-acetic
acid treatment rapidly reduces the microbial population on the fresh hides and
maintains a low level of viable organisms after application. Sulfur dioxide is the
active material in the elimination of the microbial activity (8). In aqueous solution
sulfur dioxide is present as a dissolved gas, bisulfite ion, and/or sulfite ion. The
proportion of each is dependent on the pH of the solution. At a high pH all the
sulfite is present as sulfite ion. Has no preservative effect. At a low pH all the
sulfite is present as a dissolved gas which can rapidly escape from solution.
Using acetic acid in addition to sodium sulfite results in a buffered solution of pH
4.5 At. This pH sulfur dioxide is present in equilibrium with bisulfite ion, and loss
of sulfur dioxide to the atmosphere occurs slowly. Using a closed system to
store hides provides maximum effectiveness for this method of preservation.
This paper presents a statistical analysis of a commercial trial conducted
entirely at. S. B. Foot Tannery in Red Wing, Minnesota. The study is divided into
two parts, reflecting two different methods of application of the preservative
solution. In both cases hides were held for seven days in a closed drum and
then processed normally into side-upper leather.
Processing parameters measured included raw weight, fleshed weight,
crust area, tensile strength, SATRA extension, and SATRA load. A subjective
evaluation of several aspects of the final leather quality was made by
experienced tannery personnel. The data were evaluated statistically to determine
the effect of preservation treatment. Matched side brined hides were used as
controls throughout the tests.
Twenty hides were obtained from a local packing plant and transported to
the tannery, where they were sided, marked, and weighed. The sides were
divided into test and control groups by cross-matching alternating left and right
sides. The control hides were brine cured, allowed to drain overnight, and
treated with additional safety salt. The test hides were sprayed with sulfite-acetic
acid solution in a revolving spray tunnel in a manner described by Benrud (9)
in preservation experiments using benzalkonium chloride. The spray was applied
to the skins in the tunnel at the rate of one quart of preservative solution per
side. The quantity of both sodium sulfite and acetic acid applied to each side
was one percent of the side weight.
WARNING ON SO2 : Caution must be exercise with aced solutions containing
Na2 So3 because of SO2 evolution.
After treatment the sides were placed in 55-gallon fiber barrels, covered
with an airtight lid, and held at ambient temperatures for seven days. The total
elapsed time between hide removal in the slaughterhouse and placement of the
hides in the containers was fine hours.
Two of the sulfite treated hides were stored in a separate barrel and exposed to
elevated temperatures during the test. This barrel was placed in direct sunlight
for the first three days of the test while the rest of the hide samples were kept
under cover. While in the sun the temperature inside the barrel reached slightly
over 100§ F. During the hottest part of the day. During the same period the
maximum temperature reached in the other barrels was between 80º and 84º F.
Preservation Test II
This test consisted of ten hides obtained from the same slaughterhouse, brought
to the tannery, sided, marked, and cross-matched. The control sides were
brined, and the test hides were drummed for ten minutes in a 20 percent float
containing sodium sulfite and acetic acid in an amount equal to one percent of
the weight of the sides being treated. The sides were then removed from the
drum and placed in 55-gallon fiber barrels along with the float and held for seven
days.
After storage the hides in both tests were soaked, fleshed, and processed
normally into crust leather. Half of the test sides and half of the control sides
from Preservation Test I were further processed into finished leather. The crust
area of all sides was measured.
A general subjective evaluation of the final leather from each side was made,
comparing the control sides with the test sides for break, temper, color, draw,
and veininess. Tensile strength and SATRA values were measured on all
samples by standard ALCA methods (10). Shrink temperatures were also
obtained on all samples. Each sample was examined microscopically for the
presence of vertical fiber defect, using the techniques developed by Everett (11).
The information from all measurements was stored on magnetic tape in a
computer. Statistical comparisons of each of the parameters of this test were
made using programs supplied by Com-Share Computer Utilization Company
Analysis. Analysis was done by zero order correlation evaluation of all variables
department of Agriculture over others of a similar nature not mentioned. by
sample and process, multiple and stepwise regression, and variance and
covariance analysis. For these tests, a one-way multivariate analysis of variance
proved to be the most effective means of comparing the two methods of
application of preservative solution.
The hides in the second test utilizing a drum float application of the sulfite did
not show hair looseness or difficulties in handling during processing. No wringer
roller pattern was observed on the hide at blue sort. Both the test and control
sides processed normally.
Data collected in both tests during processing consisted of the raw weight
fleshed weight, and crust area for sulfite treated and brine cured hides (Table I).
The only statistically significant difference observed was between the means for
weight after fleshing of brined and sulfite treated hides from Preservation Test I.
The sulfite treated hides showed an average weight loss of about three pounds
more than the average weight loss of the control. When the weight of the treated
hides after fleshing was corrected for the loss of hair, the difference was still
statistically different at the 95 percent level of confidence. The small differences
found in all of the other measured parameters were not significant and could
have occurred at random.
The concentration of acetic acid and sulfite in the two treatments could be
responsible for this single difference observed between the two application
procedures. Table II compares the two solutions as applied to the hides. The
significant reduction in weight after fleshing is probably due to the dehydrating
affect of the spray treatment solution. A 15 percent w/w solution of both acetic
acid
and sodium sulfite would have a dehydratitng effect similar to a 30 percent
(saturated) brine solution. In the spray treatment the hide weight difference
between treated and untreated hides before fleshing was over five pounds after
the hides were drained of treatment. This difference was significant at the 98
percent confidence level.
Physical testing of the crust and finished leather from both preservation
tests resulted in a surprising number hides having low tensile strength values in
both test and control sides (Table III). These hides showed test values ranging
from 730 to 1880 p.s.i, compared to the more normal range of values which run
from 2800 to 3200 p.s.i. These results suggested the presence of vertical fiber
defect (VFD) in these hides. Microscopic examination confirmed that at least four
hides in the first preservation test had vertical fiber defect, and two in the second
test had intermediate fiber defect, It also verified that two hides
Were incorrectly matched. Two consecutive control sides had tensile strengths
of about 3300 p.s.i., while the corresponding test sides had tensile strengths of
925 and 1320 p.s.i. VFD was present in the test sides but not in the control
sides, indicating that these sides were not matched. Data from the fully defective
hides and from the mismatched pair were not used in the statistical analysis as
presented below.
Physical differences in both Preservation Tests I and II were small. The
phyiscal test data showed no significant differences between test and control
sides in either tensile strength, SATRA extensions, or SATRA loads (table IV).
In addition to these physical tests, all samples from both preservation
methods were tested in the crust or finished leather for shrink temperature.
Again, there were no significant differences between test and control sides.
The absolute criterion on which any preservation procedure must be
judged
is its ability to meet the manufacturer's specifications for saleable quality leather.
The first preservation procedure, utilizing a spray application of the acid and
sulfite, did not meet this criterion due to a coarse break. The tanners' evaluation
of the leather included the following: temper, color, draw veininess, and break
(Table V).
All the spray treated sides except one had an unacceptable coarse break.
The control sides had the tight break associated with good quality side upper
leather. In all other aspects the treated sides were similar to the controls. Treated
sides had similar veins and temper, and less draw, and were somewhat lighter
in color compared to the control sides.
Subjective evaluation of the samples from the Preservation Test II showed
that drumming in a 20 percent float did not cause the coarse break seen in hides
which were treated in the spray tunnel. The leather produced was evaluated as
being equivalent to or better than the brine control leather in all subjective
evaluations including break.
The results of the experiment with the two hides which were placed in the
sun to provide elevated temperatures conditions were inconclusive. These two
sides, like all of the others which were treated with sulfite-acetic acid in the spray
tunnel, were judged to have an unacceptable coarse break but were similar in
all other respects. The higher temperature had no other observable effect on
these two sides. Small scale experiments performed with hide pieces indicate
that good preservation results can be achieved routinely with this system at
temperatures as high as 86º F.
The results of this study show that the proposed seven-day sulfite-acetic
acid preservation system can be adapted to a commercial situation to produce
acceptable side upper leather.
Application of one percent Na2 SO3 (Sodium sultite) and one percent
acetic acid to the raw hides by drumming for ten minutes en a 20 percent float
produced leather of high commercial quality after seven days of storage at
temperatures up to 84o F. This method did not require any alteration in the
normal production procedure.
Application of the same quantity of sulfite and acetic acid but in a more
concentrated solution by means of a spray tunnel produced leather with an
unacceptable coarse break. This does not preclude the possibility that a more
dilute spray might give the desired preservation without producing the coarse
break in the leather.
Received May 12,1976.
Mr. HOPKINS: Fleshings from brine cured hides may contain potentially
toxic biocides. The chemicals we use are both used in the food industries and
should have less problems.
Mr. De: Would you thin that the hide trimmings could be used for edible
gelatin?
Mr. HOPKINS: yes, this might be a possibility if the hides were handled
in an acceptable sanitary fashion.
Mr. ADEL Z. HANNA (Triangle Tanning Company): Was hydrogen sulfide
evolved? Could this be hazardous?
Mr. HOPKINS: We did not notice any sulfide evolution.
Mr. Hugh Hawthorn (Canada Packers Limited): What was the time lag
from take-off to treatment?
Mr. HOPKINS: Perhaps three hours.
Mr. Hawthorn: What equipment Would You use on a large scale?
Mr. HOPKINS: They were in the solution for an hour prior to hanging over
the horse.
Mr. Albert S. JAMISON (Seton Leather Company): The sulfite you used for
preservation has an oxygen demand. Did you check the BOD's of the soak
waters?
Mr. HOPKINS: No, we did not, but it does contribute to the BOD.
However, sulfite is used in some tannery beamhouses.
* This discussion followed the presentation by Mr. Hopkins of Part II of
this series at the 1974 convention. See JALCA, 70,372-9 (1975) for the paper.
Mr. JAMISON: Are we Just substituting one effluent problem for another?
Mr. HOPKINS: I don't think a significant amount will end up in the effluent
in the reduced form. Also when in contact with lime, Any remaining sulfite will
precipitate.
Mr. SATYENDRA M. De: I think that at the pH of operation, most of the
sulfite absorbed in the hide is converted to sulfate, diminishing the sulfite
chemical oxygen demand.
Mr. Guy MOBERG (Denison Hide Company): Does this cure remove water
from the hides like brining does?
Mr. HOPKINS: Some water may be removed from the hide, but basically
it does not act. Like a concentrated brine.
Mr. MOBERG: How will the hides be dried for shipment to keep shipment
weights from changing during transportation?
Mr. HOPKINS: Container packaging will have to be used to prevent the
hides from drying.
Mr. STUART E. Miller, Jr. (Salz Leathers, Inc.): You mentioned, Bill, that
your sides were wrapped in plastic bags. Was this done to maintain sterility or
for convenience?
Mr. HOPKINS: It. Was done to keep them from drying out in storage, and
also to prevent further contamination.
Mr. Miller: Were these manury hides? Do manury hides require More
chemicals?
Mr. HOPKINS: These were relatively clean cowhides. More work is needed to
develop the conditions for a practical procedure. We have shown that we can
preserve hides which were fleshed or demanured.
Dr. JEROME F. Levy (Rohm and Haas Company): In our work on fresh
hide preservation, we can distinguish between preservatives that effect a quick
kill of the hide's bacterial populations and bactericides that give long - term
preservation but are not able to reduce large initial levels of bacterial
contamination. Could you classify your process in either class?
Mr. HOPKINS: Our paper given last year gave some data on this decrease
in count. You want a mixture of the two effects. The acid condition in our system
is unfavorable to growth. We have found that by treating hide samples with just
an acid solution at a low pH we can get a rapid lowering of the microbial count;
however, in a few days, obvious occurs. The preservative effect of sulfite salts
under acid conditions is well documented.
Mr. SATYENDRA M. De: Thank you, Bill, a for most interesting paper.
Dr. Thomas C. THORSTENSEN (Thorstensen Laboratory): The Department of
Agriculture has again come through with a very significant paper and one of
considerable practical importance. The problem of short-term cure of hides is
one of the most urgent in our industry. There is a definite shift in production to
hide-producing areas and this type of cure system is in my opinion a method for
the future.
Two prior papers in this series dealt with the reduction of bacterial counts
and indicated definitely an excellent hide preservation with the sulfite-acetic acid
system. This present paper covers two experiments, one in a hide washer and
one in a drum. The results in the drum experiment were much better. The
conditions in the hide washer were chemically drastic, and poor quality leather
resulted. We must exercise care with these processes to control them properly;
but if properly controlled they seem to be very effective as a method of
preservation.
Dr. Ross G. DONOVAN (Canada packers Limited): You mentioned that the
new treatment was less expensive. Can you give us some numbers for illustrative
purposes?
Dr. BAILEY: I am using Chemical Marketing Reporter prices. The
commercial chemical prices may be less.
Mr. RUSSEL A. Launder (Pfister and Vogel Tanning Company): Dave, I
Think that the ideas has been for short -term curing. Have you considered how
long these hides could be stored?
Dr. Bailey: At Swoboda s making garment leather from the treated hides,
we reached a 28-day holding period without damage. We don't however, know
the possible length of storage that is feasible. The current work was directed
toward short-term preservation of the hides for shoe upper leather.
Dr. Thomas C. THORSTENSEN: Didn't the sulfite-acetic acid give lower
bacterial counts than the brine cure?
Dr. Bailey: Yes, the bacterial counts by our plating methods were quite a
bit lower. That does not necessarily mean that the bacteria that are present on
the brine cured hide are damaging the hide. They could be there, but innocuous.
Mr. William F. DOOLEY (Armira Corporation): Dave, do you have any
thoughts on the effects of prewashing the stock off the kill floor prior to
application of the preservative?
Dr. Bailey: Any treatment like that will lower the bacterial count, so it
should be of some assistance.
Dr. Thomas C. THORSTENSEN: Thank You, Dave, for a very excellent
paper.
** This discussion followed the presentation by Dr. Bailey of part III of this series
at the 1975 Convention. Part III is published on preceding pages in this Journal
issue.
General Index
Abstract
Introduction
Experimental
Results and Discussion
References
Discussion
List of tables
Abstract
Fresh cowhides were Treated with solutions of sodium sulfite and acetic acid by
two different methods. Some of the hides were treated by drumming in a 20
percent float; the others were treated with a more concentrated solution in a
spray tunnel. After storage for seven days in closed barrels at ambient
temperatures, the hides were processed into side upper leather without
modification of standard tannery processes.
Introduction
Nonsalt preservation of hides and skins offers at least two advantages to the
tanning and packing industry. A successful method would significantly reduce
the dissolved solids content of tannery effluents, thereby reducing the cost of
Experimental
Preservation Test I
Results and Discussion
The first preservation method utilizing the spray tunnel resulted in the hair
becoming very loose after seven days. It was estimated that 70 percent of the
hair was removed during the soaking and fleshing operation . the hides were
slippery and difficult to handle during fleshing. At blue sort it was observed
immediately after wringing that the wringer roller surface pattern had been
embossed into the grain layer of the sulfite treated sides. The brined control
sides processed normally.
References
JALCA, 66,161 (1971).
Discussion
Mr. SATYENDRA m. De (Chestnut Operating Company): Thank you, Bill for an
excellent paper. This is an important subject, and one on which we should look
ahead since sodium chloride can potentially give so many problems as the
source of dissolved solids in beamhouse effluents. Bill, I would like to ask you
how the fleshings or trimmings secured from your process will compare to those
from brine cured hide?
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