Grinding
10
Dec 2002
Dear Steve and others
I was looking for grinding and milling equipments in the Exhibit Room
on GSA Denver 2002. There was a Booth #421 exhibiting this type of equipment.
Here is the information: ----------------------------------
SPEX CertiPrep 6750 FREEZER/MILL The 6750 Freezer/Mill from SPEX CertiPrep
is an updated version of the classic SPEX CertiPrep 6700 cryogenic mill.
The 6750 is used on samples normally considered difficult or impossible
to grind at ambient temperatures: polymers, wood, bone, tissue, rubber,
and the like. The Freezer/Mill embrittles samples by immersing the grinding
vial in liquid nitrogen, and then pulverizes them with a magnetically
driven impactor. The samples, up to several grams in weight, are isolated
in a sealed vial during grinding, which rarely takes more than several
minutes. Grinding vials can be pre-cooled to achieve throughput of 10
or more samples per hour; low temperatures are retained throughout,
preserving structural and compositional aspects degraded or volatilized
during room-temperature grinding.
Telephone: 1-800-LAB-SPEX
or (732) 549-7144
Fax: (732) 603-9647
Email: CertiPrep@spexcsp.com
http://www.spexcsp.com
Since I didn't have chance
try that type of mill on the show, I don't know its performance. But
I saw some plant samples they ground on exhibition. The sample grain
size looks meeting my requirement for cellulose extraction. The Exhibitor
told this equipment does make big noise.
--------------------------
Zheng-Hua
Dr Zheng-Hua Li
Stable Isotope Lab
Dept of Geological Sciences
Uni of Tennessee
Knoxville, TN 37996
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10 Dec 2002
Had to try this again since pics wouldn't go to list:
Steve & group,
We use two refurbished Erbach
(E-300?) ORBITAL shakers. Recently picked up a 1960 New Brunswick G-10
model too. Vintage. All three we have were purchased through university
surplus. New price for these heavy-duty models is over $3k! Make sure
their not reciprocal shakers if you find used ones.
The top plate has been modified
(differently on each one) to hold Gerberbaby food jars. These are expendible,
cheap, readily available and have nice curved inner edges for ball/jar
surface contact. IMPORTANT: We wrap a strip of packing tape around the
lower half and base of the jars to retain sample material if it breaks.
One shaker has a heavy foam
block (see pics; plastic bags you see in 4th pic are baggies used before
the packing tape idea) on the top platform withdoorknob holes drilled
in for jars. The other two use the standardErlenmeyer flask metal clips
that came with them originally, which have been bent a bit to fit. Inside
jars we put 2 stainless-steel balls (0.5" and 0.75" diam).
Lids get label tape to id. The amount of material you add should just
cover the floor of the jar. Too little leaves a mound in the center
unground; too much inhibits ball movement.
We run them at low speed
only; overnight for most dry leaf/needles. Wood must be 'thoroughly'
preground on a Wiley mill before going on the shaker. Wood usually needs
several days grinding. Mortar and pestle with liquidnitrogen are kept
handy for the ones that are insufficiently ground (still this is tough).
Overall, this works great
for dry plant material. Somewhat less effective for wood. The Wiley
pregrinding is key for wood but has high material loss.
Bob
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Robert D. Stickrod II, Lab Manager Idaho Stable Isotopes Laboratory
University of Idaho, Forest Resources CNR 214, 6th & Line St. Moscow,
ID
83844-1133, USA (208) 885-6512 lab (208) 885-6226 fax (509) 338-2814
cell
www.cnr.uidaho.edu/isil
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11 Dec 2002
Hi Steve and other tree ringers
Todd Dawson turned me on
to a grinding method that I have found to be quite good and cheap. Essentially
we are using a ball mill called a Wig-L-Bug. It is made by Crescent
(industrial model C32003A) and can be found from dental supply houses
(Dentsply) and costs only about $370. I would highly recommend purchasing
spare "long arms" as they tend to break periodically (only
$3 each). It comes with a simple timer and anywhere from 5 to 10 minutes
will produce powdered wood samples.
We use 3/16 inch ball bearings
(very cheap) that we clean will a sonic bath. We use disposable 1 ml
cryotubes (NUNC Brand #375299, about $160 for a pack of 500) that fit
well onto the Wig-L-Bug. The cryotubes appear sturdy enough for the
shaking but occasionally the seam may crack (we add some tape to the
end and have never lost a sample). The other thing I like is that the
cryotube mates perfectly with a 1.5 ml epindorph tube (which is what
I store my samples in) so transferring material into and out of the
tube is pretty easy. The tube can hold up to 100 mg of wood at a time.
The other advantage of a ball mill is that the sample is homogenized
as well as ground, so subsampling is less of an issue. If you have multiple
ball mills and fairly soft wood at least 20 to 30 samples could be ground
per hour.
I have yet to process very
small samples and getting enough of the powder out of the cryotube could
be problematic. I have found that about 4 to 5 mg of powder cannot be
extracted from the cryotube. Most of my samples are about 60 to 80 mg
so the loss is acceptable at this point. The losses are better, in my
opinion, than those from a Wiley mill. To avoid losses in grinding,
I have contemplated for very narrow tree rings (< 0.5 mm), cutting
the ring portion of interest into very narrow slices and placing them
directly into the filter bags for processing and then using a blade
to cut up the cellulose for loading into capsules. Has anyone done this
and does the cellulose extraction procedure have to run longer to process
slices?
To optimize Wig-L-Bug usage
the wood needs to be completely dry and cut into small pieces (large
chunks will take much longer). Generally, I cut out the latewood or
earlywood under a dissecting scope with a scalpel and then take the
slices and cut them into small pieces with a razor blade, place them
in an epindorph tube, dry them overnight and then grind them the next
day. I am using the filter bag/soxhlet method and there is some concern
that the powder is so fine that it will pass through the pores of the
filter bag. However, I have found that I get comparable yields from
the powder as compared to coarse samples (25-27% compared to 27-33%).
The reduction in extraction time for powdered samples as compared to
coarse samples makes these losses acceptable, but also something to
consider when dealing with small amounts of material (again, I may not
grind very narrow slices). The fineness of the powder is a function
of the time in the ball mill, so some tests should be run to determine
what works best. Hardwoods or latewood would obviously take longer to
grind than softwoods or earlywood (helps to place very fine pieces of
hardwood in the mill, whereas softer woods could have larger chunks).
That's all I can think of.
Happy Grinding and Merry Christmas to all!
John Roden
Associate Professor
Department of Biology
Southern Oregon University
Ashland, OR, 97520
rodenj@sou.edu
voice: 541-552-6798
fax: 541-552-6415
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12 Dec 2002
Dear John and others,
> To avoid losses in grinding, I have contemplated for very narrow
tree rings (< 0.5 mm), cutting the ring portion of interest into
very narrow slices and placing them directly into the filter bags for
processing and then using a blade to cut up the cellulose for loading
into capsules. Has anyone done this and does the cellulose extraction
procedure have to run longer to process slices?
As we are working with small
wood samples (10-30 mg), we tested possibility to perform cellulose
extraction on coarse samples (0.1-0.3mm thick slices and wood shreds)
in order to avoid large losses due to grinding (we are using the Retsch
Mixer Mill MM200 with 10 ml stainless steel jars). After a 2-day bleaching
step, these samples (Jack pine) appear perfectly white, just as the
ground ones. No isotopes analysis have been performed on them yet.
> I am using the filter
bag/soxhlet method and there is some concern that the powder is so fine
that it will pass through the pores of the filter bag. However, I have
found that I get comparable yields from the powder as compared to coarse
samples (25-27% compared to 27-33%). The reduction in extraction time
for powdered samples as compared to coarse samples makes these losses
acceptable, but also something to consider when dealing with small amounts
of material (again, I may not grind very narrow slices). The fineness
of the powder is a function of the time in the ball mill, so some tests
should be run to
We obtained a very fine powder
with the MM200, but losses can be too important with our smallest samples
as 5 mg in average stay in the jars (which sometimes correspond to 50%
of our sample). Actually, grinding yield depends largely on the wood
quality (i.e. large inter-specific variations, but no evident difference
between sapwood and heartwood for coniferous species).
After some tests, we abandoned
the idea to use F57 Ankom filters because of their too large porosity
(30 microns) causing important yield decrease (especially during the
step of removing of hemicelluloses by NaOH). I used to use teflon pouches
(Alltech Pre-cut membranes 1 um PTFE 47mm 100/CAN $127.00 Part.2059).
These filters are very resistant and can be used several times after
careful washing. However, we recently had to switch to the 0.45 micron
model (Part. 2058) because of serious delivery time problems with the
supplier for the 0.1 um one. This 0.45 um model seems to be suitable
too, but we don't really know what should be the minimum pore size to
allow good diffusion of the extracts (i.e. lignins and hemicellulose
fragments). Our alpha-cellulose yield is quite high (between 25% and
37%, according to the species), but we don't know if it is due to very
small losses or mediocre hemicelluloses extraction.
Regards,
Stephane Ponton
Stéphane Ponton, PhD
Department of Biological Sciences
University of Lethbridge
4401 University Drive
Lethbridge, Alberta T1K 3M4, Canada
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28 Jan 2003
Hello,
Here is an addition to the previous discussion about sample reduction
(grinding/maceration/etc.). I have been looking for equipment that will
reduce small whole wood samples (30mg-50mg) to a particle size of less
than 150 microns in a single procedure, with very small sample loss.
The size constraint is based on a paper by Borella et al. (1998).
Borella, S., M. Leuenberger, M. Saurer, and R. Siegwolf, Controlling
uncertainties in d13C analysis of tree rings: pooling, mixing and cellulose
extraction, Journal of Geophysical Research, 103 (D16), 19519-19526,
1998.
So far I have two trials to report:
Gilson Company, Fritsch LC-140 Rotor-Speed Mill (called "pulverisette
14" by Fritsch)
I arranged to have samples of spruce ground at Gilson Company, Lewis
Center, Ohio. This model was recommended to me by the technicians at
Gilson after hearing about the desired particle size and beginning sample
size constraints. The spruce I sent them was pre-ground to 20 mesh (840
microns).
I wanted the material ground in a single step, but my instructions were
apparently not clear, as they tested the grinding in a 3-step procedure
as follows:
(a) Initial grinding on 0.20mm sieve (200 microns); 20% retained on
a 106 micron sieve, 80% passed through.
(b) Half of the material was then ground on a 0.08mm (800 micron) sieve.
After grinding, almost all material passed through the 106
micron sieve, about 14% was retained on a 75 micron sieve, and about
85% passed through the 75 micron sieve.
(c) As a final test, they used 5mg samples from (b), and tested the
equipment for amount recovered. At 20,000 rpm, about 80%
was recovered. At 10,000 rpm, 100% of the 5mg was recovered.
According to the technician at Gilson, cleaning the mill between samples
would take "a matter of minutes". From the cleaning description
I would estimate 5+ minutes. I am told that underneath the rotor there
are some ringed grooves. Material will accumulate in these grooves,
and should be cleaned out using a wire brush. (This suggests one place
where sample would be lost.) Another potential problem is buildup of
static electricity on the metal parts. (Static electricity is a particular
problem where wood particles are concerned.) The technician said that
they sometimes use micronized silica to reduce the static, but admitted
that it doesn't always work.
In subsequent email with the technician I was told that grinding a 50mg
sample from 20 mesh (840microns) to <150microns would take about
10 seconds. Also, a titanium conversion kit (expensive) is available
for "iron-free" grinding.
In summary, this equipment appears to be more than adequate for the
grinding of whole wood to an acceptable particle size and the grinding
is very fast. The cost of this mill is $5645. The accessories used for
these tests were: (1) a 24-rib stainless steel rotor, $1340, (2) a 20mm
sieve ring, $131, and (3) an 8mm sieve ring, $131. Only one sieve ring
would be required, so the total cost to be operational would be $7116.
The problems I see with this system are sample loss caused by a non-sealed
system and by the effects of static electricity, and between-sample
"downtime"..
The URL for this company is
www.globalgilson.com
SPEX certiprep, 6750 Freezer Mill
I visited SPEX certiprep, in Metuchen, New Jersey, twice to test their
6750 Freezer Mill. This model is an impact mill, using electromagnets
to shuttle a steel rod from one end to the other of steel cylinders,
fitted with end caps. The setup uses liquid nitrogen to both cool the
electromagnets and the sample(s). This mill can run 3 small samples
at once using microvials, though the microvials use smaller rods, so
the force of the impact is less. The sample capacity of the microvials
is 0.1-0.5ml. Larger vials can accomodate samples of 0.5-4.0ml, but
only 1 sample can be ground at a time.
The recommended grinding procedure is a 15-minute initial cooldown (this
would be less for subsequent samples), and 3 2-minute impact sessions
separated by 2 2-minute cooldown periods. I did not experiment to see
if the same results could be obtained if these times were reduced. Given
the specifications above, the per-sample grinding time using the microvials
is about 5 minutes (assuming an average of 5 minutes for the cooldown).
I tested this mill with (1) the same spruce sent to Gilson, (2) thick
slices from a 5.0mm dried conifer core, (3) thick slices from a 5.0mm
fresh conifer core, and (4) approx. 3-8mm segments of fresh conifer
needles. In almost all cases, the Freezer Mill was able to reduce the
material to much less than 150microns. This is a somewhat subjective
assessment, as I did not have the equipment necessary for a particle
analysis, but the final product was much finer than material described
as <106microns from the trial at Gilson. The only failure of the
equipment occurred when I placed over 100mg of thick increment-core
slices into one of the microvials.
Reduction of that sample size to 50mg resulted in a very fine final
particle size.
Because the grinding system is closed, the percentage of sample recovered
depended entirely on operator error in opening the vials, not loss during
grinding. The samples were easier to recover if the vials were warmed
to room temperature before the vials were opened. The microvials were
not always easy to open, sometimes requiring two pairs of pliers, or
similar, to remove the endcaps. The endcaps are machined as press fit,
so a tight fit is desirable, but the company needs to come up with a
simpler design for opening the vials. With care, one could recover well
over 90% of any sample.
I used the vials they had been experimenting with in their testing lab.
I did not carefully clean their vials before use, and they had been
run for a long time without samples in them immediately prior to our
use. The inside of older vials show some wear from the impactors hitting
the sides of the cylinder. The samples showed some discoloration after
the first run; probably caused by contact of the sample material with
the inside of the steel vials. Subsequent uses of the vials did not
show significant
discoloration, but some material from the inside of the vials was probably
present. Cellulose extraction should remove this contaminant, but it
may be a concern if whole plant material is to be analyzed.
I recommend this mill for the grinding of small botanical samples, with
two caveats. The mill is very loud when running and a ready supply of
liquid nitrogen must be available during milling. Also, sieves are not
part of this method, so production of samples of a certain range of
particle sizes is not possible using this equipment.
The cost of this mill is $4100, with large vials being $165, and a set
of 3 small vials being $465. I would recommend at least 3 of each type
of vial or vial set, to reduce the downtime during processing, thereby
reducing both the total processing time and the liquid nitrogen cost.
The total cost to be operational for small samples would be $4565, though
additional sets of vials are recommended.
The problems that I see with the SPEX Freezer Mill are:
(1) the Liquid Nitrogen cost, and (2) sample loss. The vials are a press
fitting, so you have to be very careful opening the vials, or you lose
sample. We weighed the samples before and after, and found about a 10%
loss. However, the samples were not dried before grinding, so it's possible
that water was pulled out of the wood during the cooldown before grinding.
Also, additional care in sample recovery might have increased the yield.
There was also a discoloration in the final product, apparently from
the steel of the vials. We did not carefully clean their vials before
use, and they had been run for a long time without samples in them immediately
prior to our use. I don't have evidence that any powder from the interaction
of the grinding rod and the vial would be removed during processing
to cellulose, but I expect that this would be the case.
The URL for this company is
http://www.spexcsp.com/
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Dr. William E. Wright
Postdoctoral Fellow
Lamont-Doherty Earth Observatory
of Columbia University
61 Route 9W
Palisades, New York, USA
10964-1000
Phone: (845) 365-8441
FAX: (845) 365-8510
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___________________________________________________________________________________________________________
18 Jan 2004
A while ago I reported homogenization results for whole wood maceration
using a cryogenic impact grinder built by SPEX CertiPrep. While I stand
by my statements about the small particle size, and, therefore, the
high degree of homogeneity in the resulting product, I must issue a
caveat. I later found that grinding with this machine could produce
wood flour with such a small particle size that much if not all of the
test sample was lost through the pouching matrix during extraction.
After experimenting with the grinding time, I was able to ensure that
most of the particle sizes in the resulting product were between about
25 microns (the mesh size of the pouching material) and about 125 microns
(e.g. Borella et al., 1998). (The upper end was not quantified. It was
an estimate based on comparison of the post-grinding product with material
passed through a 120 mesh sieve... 120 mesh=125 microns) (note: the
amount of cellulose recovered after extraction plotted as a linear function
against the time of grinding.)
That said, an internal cellulose
standard produced from whole wood, using the SPEX equipment, currently
has a standard deviation of less than 0.1 per mil for d18O.
Regards,
Ed Wright
--
/ / / /:/ / / / / / / / / /./ / / / / / / / / /./ / / / / / / / / /./
Dr. William E. Wright
Postdoctoral Fellow
14A Marine Biology
Lamont-Doherty Earth Observatory
of Columbia University
61 Route 9W
Palisades, New York, USA
10964-1000
Phone: (845) 365-8441
FAX: (845) 365-8150
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