.
I
An Environmentally Acceptable Solvent
Based On nomtal-Propyl Bromide
Ronald L. Shubkm, Ph.D.
R&D Advisor
and
Eric W. Limatta, Ph.D.
R&D Specialist
Albemarle Corporation
Presented In Part at the:
Eighth Annual International Workshop On Solvent Substitution
December 2-5, 1997
Scottsdale, Arizona
ALBEMARLE
C O R P O R A T I O N
TM
Cleaning Solvents Based On normal-Propyl Bromide
Ronald L. Shubkin, Ph.D.
normal-Propyl bromide (nPB) has begun to attract wide interest as an environmentally
acceptable alternative to chlorocarbons, hydrochlorocarbons and chlorofluorocarbons. In
addition to its aggressive cleaning performance, nPB has a very low Ozone Depletion Potential
and a very low Global Warming Potential. It has no Flash Point by either the Tag Closed Cup
or Open Cup methods. Applications for nPB-based cleaners include vapor degreasing, cold
cleaning and ultrasonic cleaning of complex metal parts, circuit boards, electronic components,
implantable prosthetic devices, optical equipment and others. A discussion of toxicological,
environmental and regulatory considerations is included. Case histories will illustrate the
broad applicability of nPB-based cleaners.
m r o d u c t io0
The introduction of chlorinated solvents provided manufacturers and fabricators a
convenient and economical way to clean a host of difficult soils from strategic parts. Efficient
cleaning, rapid drying, low flammability, residue free parts and relatively low solvent costs all
contributed to the popularity of chlorocarbon fluids. However, many chlorine containing solvents
have now been banned or restricted because of environmental and/or health considerations. In the
search to find suitable alternatives, a wide variety of new solvents were developed'. Many of the
new solvent cleaners do excellent jobs, but still suffer from one or more deficiencies relative to the
overall costlperformance of the chlorinated materials they replaced. Even some of the newer
solvents, such as some hydrochloroflouorocarbons (HCFCs), have been shown to have
environmental problems and have been banned from usage in cleaning applications.
Background
In 1991, the total U.S. market for 1,1,1-trichloroethane(TCA) as a cleaning solvent was
700 MM Ibs. Another 200 MM Ibs was sold as an emissive solvent. TCA was very effective and
very popular as a cleaning solvent, but it suffers from two important drawbacks relative to
environmental considerations. It has a relatively high Ozone Depletion Potential and a relatively
high Global Warming Potential. The manufacture of TCA was banned by the Montreal Protocol
effective January 1, 1996.
Identification of an across the board replacement for TCA has proved to be a formidable
task, and a fragmentation of the cleaning market has resulted.' Different products and procedures
have been developed for different applications, but not all of these have proven to be wholly
satisfactory. As an example, the hydrochlorofluorocarbon HCFC-141 b was introduced and
seemed satisfactory for a number of niche applications, but it was banned from use as a cleaning
agent effective January 1, 1997. It may still be used as a refrigerant.
A host of new cleaning systems have been introduced in recent years to meet the
Page 2
challenges presented by today's industrial cleaning requirements. All of the new systems offer
advantages in specified niche applications, but none have met all of the requirements of the
I
marketplace. Some of the important alternatives are:
Alternative chlorocarbon solvents. Most chlorinated solvents are effective cleaning
agents. However, most have either been banned from manufacture, restricted to specified
uses, or scheduled for phase-out.
Hydrocarbons and oxygenated hydrocarbons. These solvents have the obvious advantage
of low cost. However, they are readily flammable and present serious hazards when used
in cleaning operations.
Hydrochlorofluorocarbons (HCFCs). As with many chlorocarbon solvents, the most
popular of these (HCFC-14lb) has been restricted to non-cleaning applications. Other
examples are too expensive, too volatile, or have only moderate cleaning ability.
Fluorocarbons. Fluorocarbons are non-toxic, non-flammable and very safe to use. They
are also very expensive and have poor solvency for most soils.
Hydrofluorocarbons (HFCs). HFCs have moderate solvency but are expensive. They are
excellent for niche applications that can tolerate the high price.
Hydrofluoroethers (HFEs). HFEs are similar to HFCs in solvency and cost.
Volatile methyl siloxanes (VMSs). VMSs, such as hexamethyldisiloxane, are low in
toxicity and contain no halogen atoms. They are chemically very stable. On the other
hand, they have flash points and only moderate solvency -- and they are expensive.
Semi-aqueous systems. The problem of proper disposal of semi-aqueous systems is often
overlooked. Because of the high organic content, it is not appropriate (or legal in most
cases) to dispose of these systems down the drain. Separation and recycle of the organic
phase is usually difficult and is not cost-efficient. Slow drying and potential corrosion
problems may also come into play.
Aqueous systems. Aqueous systems are very inexpensive in terms of cleaner cost, but
they are not suitable for many applications. Slow drying and residues on the clean parts
are two major problems. Corrosion of metal parts may also be a factor. Finally, electrical
and electronic applications usually cannot tolerate the presence of any remaining traces of
water.
No clean systems. Some manufacturers have eliminated the need to clean at various
stages of manufacture. Sometimes this requires a change in the manufacturing process or
the order of assembly.
l
r
iv
1
n i e
A new solvent/cleaner based on normal-propyl bromide (nPB) has been developed to meet
the needs of those who require the cleaning efficiency of the chlorinated solvents, but who must
meet the strict environmental standards for a replacement solvent.* The new solvent/cleaner does
not suffer from many of the short-comings of other alternative solvents that have been offered to
the market. nF'B is an effective cleaning agent. It is safe to use under the proper conditions, has a
low ODP and a low GWP, and it is not regulated under most environmental and worker safety
Page 3
rules. It is compatible with metals, has a low tendency to cause corrosion and may be used in
most current vapor degreasing equipment. It is easily recycled and is moderately priced.
Physical PropTable I compares the physical properties of nPB to two hydrochlorocarbons and two
hydrochlorofluorocarbons. HCFC-14lb is CH3-CCI2F, and HCFC-225 is a mixture of the two
isomers CF,-CF,-CHCI, and CF,CI-CF,-CHCLF. The physical properties of the nPB are similar to
all four of these solvents, but particularly so to TCA.
Latent Heat of
Vap., caVgm
58.8
57.5
57.2
52.3
33
Sol. in Water,
g d 1 0 0 gms water
0.24
0.07
0.11
0.18
0.033
Sol. of Water,
gmd100 gms solv.
0.05
0.05
0.03
0.042
0.03
Surface Tension,
25"C, dynedcm
25.9
25.6
26.4
19.3
16.2
Flash Point,
TCC, "C
None
None
None
None
None
Flammability Limits,
volume ?LO
4-7.8
7-13
8-10.5
7.6-17.7
None
Page 4
ng
-
Power
Indicators that relate to the cleaning ability of a solvent are the solubility parameters
These are the Hildebrand Parameter, the Kauri Butanol Number and the Hansen Parameters As
indicated by the data in Table 11, these values for nPB compare quite well to the common
chlorocarbons.
TABLE II
1
Hansen
Parameters:
Non-Polar"
16.0
17.0
18.0
18.2
19.0
Polar"
6.5
4.3
3.1
6.3
65
Hydrogen
Bonding"
4.7
2.1
5.3
6.1
2.9
Page 5
performance in removing polyol esters This experimental results are consistent with the Hansen
Parameters which show that nPB has a slightly lower value for non-polar materials and higher
I
values for polar and hydrogen bonding compounds.
The cleaning power of nPB based cleaners is clearly equivalent to the popular chlorinated
solvents that have been banned or restricted. Comparisons to the new alternative solvents that
have been introduced to replace the chlorinated materials are even more dramatic. Again, it is
instructive to first compare the relative solvency power of nPB to some of the new solvents that
are being offered in the cleaning market.
Table I11 compares the Kauri Butanol Number of nPB to decafluoropentane (DuPont
Vertrelm XF), perfluorobutylmethyl ether (3M HFE 7100), dichloropentafluoropropane (Asahi
Glass AK-225) and hexamethyldisiloxane(Dow Coming OS-10). By this one measure, superior
performance is expected from the cleaning formulations based on nPB.
/I
I
I
fiQka.u
normal-Propyl Bromide
(Albemarle ABZOLTMCleaners)
Decafluoropentane
(Vertrel" XF)
Perfluorobutylmethylether
(3M HFE-7100)
w t a n o l Number
I
I
I
125
9
10
Dichloropentafluoropropane
(Asahi Glass AK-225)
31
Hexamethyldisiloxane
(Dow Coming OS-10)
17
Page 6
Ranking Relative to ABZOLTMVG Cleaner
4.7
AEZOLTMVG Cleaner
E4 1,1,1-Trichloroethane
Trichloroethylene
Perchloroethylene
Methylene Chloride
Graoh 1. Relative cleaning performance of a klly formulated cleaning solvent based on nPB and
some of
~
ABZOL VG
H Vertrel XF
HFE-7100
AK-225
os-IO
Graph 2. Relative cleaning performance of a hlly formulated cleaning solvent based on nPB and
a selection of other new alternative solvents.
Page 7
Cleaning of Electronics Components
The electronics industry faces some cleaning challenges not found in other types of
cleaning applications. In particular, it is of utmost importance that ionic residues remaining on
integrated circuit boards after soldering operations be removed to very low levels. Cleaners based
on nPB and formulated for vapor degreasing have proven to be surprisingly good at the removal
of ionics. However, a new formulation designed specifically for the electronics industry ha5
recently been introduced. ABZOLTMEG Cleaner is a narrow boiling range (azeotropic or near
azeotropic) blend of nPB, a specifically selected alcohol, and the appropriate levels of stabilizers.
Two independent experiments have demonstrated the high efficiency of the ABZOLm EG
Cleaner formulation for the removal of ionic residues from circuit boards. In one experiment,
circuit boards were prepared by a potential customer. They were cleaned and evaluated for
cleanliness at Detrex Corporation using an Omega Meter. In the second, circuit boards were
prepared by Contamination Studies Laboratories (CSL). These boards were cleaned at the
Albemarle Technical Center and returned to CSL for evaluation by the Omega Meter and by Ion
Chromatography.
The circuit boards prepared by the potential customer were made of polyimide and were
6"x7" with solder mask on both sides. Each board contained twelve 20-pin LCCs (Leadless Chip
Carriers) and two 68-pin LCCs. The LCCs had 50 mil pitch centers (distance between leads).
The boards prepared by CSL were JPC-B-36 boards. First they were pre-cleaned to less than 0.1
microgradsqh of NaCl residues. Alpha Metals RA321 RA solder paste was hand applied to
the test pads. The paste was reflowed in an oven in the usual fashion. M e r cooling, the boards
were sprayed with Kester 1585-Mil RA flux and again reflowed.
The cleaning process at Detrex emulated an in-line process at the customer which included
immersion in the boiling solvent for 100 seconds and the use of spray wands. The cleaning
process at Albemarle employed a batch vapor degreaser with three minutes immersion in the boil
sump. Three circuit boards were cleaned by each combination of cleaning process and evaluation.
The levels of ionic contamination found on the boards were:
I2Qad.m
Detrex
CSL
Meter
4.4 pgms/in2
3.9
shmahwx
2.30 pgms/in2
1
2
3.10
3
fiA
2.70 pgms/in2
Ave.
4.9 pgms/in2
Standard Requirements
Mil-C-28809
<14.0 pgms/in2
Mil-STD-2000
<14.0
NASA NHB 5300.4 (3A-7) <10.0
m
CSL
Ion Chromatography
2.87 pgms/in2
2.18
2.55
2.55 pgms/in2
Page 8
Contamination Studies Laboratory noted in their report that the maximum historically
acceptable level for ionic contaminants is 14.0 pgms/in2(see Mil specs above). The report
judges ABZOLTM EG Clemer to perform better than the Freon TMS benchmark.
Evaaoration Rates
From the standpoint of raw material costs, the most economical class of substitutes for
chlorinated solvents are aqueous systems. These cleaning systems suffer from two major
drawbacks. The first is that they employ non-volatile surfactants and thus have a potential for
leaving a residue. The second is the slow drying. The latter can be improved only by the
installation of specialized drying equipment. Cleaning systems based on nPB have drying rates
that are comparable to the chlorinated solvents. To compare evaporation rates, loss of weight
from 2 ml of solvent at room temperature (24°C) was measured after five minutes. Graph 3
compares the relative rate of evaporation of an ABZOLW Cleaner to four common chlorinated
solvents.
Evaporation Rates Relative to l,l,l-Trichloroethane, RT
"
Relative Rates
Evaporation rates from normalized weight loss of 2 mL of sobent
afler 5 minutes at room temperature.
Graph 3 . Relative rates of evaporation for nPB based cleaners and chlorinated solvents
Thermal Stability
A knowledge of the thermal stability and thermal degradation products of a new solvent is
important for safety considerations during use. Buildup of contaminants on heating elements, for
instance, can cause localized hot spots that may degrade the solvent. It is important to know at
what temperature this will occur and to insure that the products of the degradation are not
dangerous or highly toxic. Two different approaches were taken to determine thermal stability.
Page 9
Thermal degradation studies were conducted by Columbia Scientific using the
Accelerating Rate Calorimetry (ARC) method. This method identifies the temperature for the
onset of degradation by detecting the accompanying exotherm. For ABZOLTMVG Cleaner (a
hlly formulated commercial cleaner based on nPB), a significant exotherm occurred at 2265°C.
The test was terminated at 347°C. For ABZOLTMPS (nPB containing no additives), no
exotherm was reported up to 395°C. However, the final pressure of the bomb after it was cooled
was considerably higher than for the VG sample. Scrutiny of the temperature and pressure data
shows that the temperature curve for the ABZOLw PS Cleaner flattened briefly at 226.5"C and
that the rate of increase in pressure increased simultaneously. A possible interpretation of the data
is that nPB thermally degrades at 226.5"C, but the event is either endothermic or it is slightly
exothermic and is not detected by the ARC instrument. In the case of the ABZOLm VG Cleaner,
which contains stabilizers, the products of the degradation react exothermically with one or more
of the stabilizers present.
The degradation products formed in the experiments described above were trapped in a
stainless steel bomb and analyzed by gas chromatographyhass spectrometry ( G U M S ) . The
products are essentially the same from both the stabilized and the unstabilized nPB, although the
ratios of the products are somewhat different. No free bromine or HBr is detected. Although
trace amounts of methyl bromide and benzene are found, no products of a highly toxic nature
form in significant quantities. Unlike chlorinated solvents, it is impossible to produce an
extremely toxic compound such as phosgene.
The second approach to determining thermal stability was to simulate a real world failure
of a heating element in a vapor degreaser'. A coiled nichrome wire was immersed in ABZOLTM
VG Cleaner in the bottom of a 250 ml flask. The flask was connected to a dry ice/acetone trap
which was vented to a laboratory hood. Electric current was passed through the nichrome wire
until the exposed part glowed red hot. The cleaning solution boiled vigorously. The vaporized
products were collected in the trap and analyzed by GCMS Unlike the ARC experiment that
was conducted in the absence of air, some of the products formed in this experiment contain
oxygen.
The decomposition products detected after the two experiments were:
ARC Method
Propane
Isobutane
Butane
Methyl bromide
2-Methyl butane
Pentane
Ethyl bromide
Branched C,H,, isomers
Isopropyl bromide
Submereed Nichrome Wire
Propene
Methyl bromide
Ethyl bromide
Benzene
Toluene
Dipropyl ether
1,3,5-Trioxacycloheptane
4-Bromo-2-butanol
4-Bromo- 1-butanol
Page 10
Excessively high temperature “hot spots” on the interior walls of a vapor degreaser can
occur if the heating elements short circuit. The thermal degradation studies show that the use of
ABZOLW Cleaners creates no risks that are not normally encountered in the event of
catastrophic equipment failure.
..
Qrrosmitv of HBr
Because hydrolysis of nPB produces HBr, while hydrolysis of chlorocarbons produces.
HCI, it was important to determine the relative corrosivity of the two acids. Corrosion tests were
carried out on carbon steel (CS) and stainless steel (SS) under static conditions. Two
concentrations (saturated and dilute) and two temperatures (25 and 53°C) were used. HJ3r is less
corrosive under all four of these conditions. The results are given in Table IV:
TABLE IV
Hvdrolvsis of nPB
Laboratory tests show that nPB is subject to a small degree of hydrolysis when contacted
with water for extended times, particularly at elevated temperatures. In laboratory tests, a hlly
formulated nPB cleaning solvent was compared with a hlly formulated l,l, 1-trichloroethane
(TCA) cleaning solvent. After refluxing with water for 164 Ius, the layers were separated and
analyzed. The nPB formulation showed 2-3 times as much hydrolysis as the TCA. These results
are something of a trade-off with the corrosion data. nPB is more susceptible to hydrolysis than
TCA, but is less corrosive if hydrolysis takes place.
Materials o f Construction - Comoatih
‘ ilitv wi th MetaIs and Drum Linin
ABZOLTMVG Cleaner was tested for compatibility with metals according to Mil-T81533A 4.4.9. This is a metal corrosion test that was originally designed to test the suitability of
TCA for military applications, The metal coupon is held half-submerged in the refluxing cleaning
fluid for 24 hrs. It is then examined for signs of corrosion All of the following metals passed this
test:
Page 1 1
Nickel
Inconel
Brass
Copper
Monel
Aluminum
Stainless steel 3 16L
Titanium
Zinc
Taqtalum
Carbon steel 1010
Fresh aluminum surfaces react immediately with 1, 1,l-trichloroethane. n-Propyl bromide
is much less reactive towards aluminum. If an aluminum coupon is scratched beneath the surface
of TCA which contains no metal passivators, there is an immediate formation of a dark, brownish
red color. If the test is repeated using nPB, no color formation is observed for several hours. At
reflux, some small dark spots are observed on the edges of the aluminum coupons after three to
four hours. Fully formulated nPB is completely safe for use with aluminum and other active
metals.
In addition to the corrosion test, two month immersion studies were carried out at 130°F
with carbon steel 1010, stainless steel 316 and high baked phenolic linings. All of these materials
were shown to be suitable for long-term storage of cleaning fluids containing nPB. Most
perfluorinated plastics are also suitable for storage.
w b i l i t y With Plastics and El
a
w
Plastics and elastomers that pass short term compatibility tests (immersion in boiling
solvent for fifteen minutes) include the following:
l?!.wtk
Elastomers
AcculamTMepoxy glass
AlathonTM HDPE
DelrinTMacetal*
KynarTMpolyvinyl fluoride*
NylonTM(6 and 6.6)
Phenolics*
Polyester (filled & unfilled)
Polypropylene
Teflonm PTFE*
T e f z e P ethylene/PTFE*
XLPEm crosslinked PE
AdipreneTM polyurethane
AflasTM PTFE
Buna-NTM rubber
KalrezTMfluorelastomer*
NeopreneTMpolychloroprene
Viton-ATMfluoroelastomer**
Viton-BTM fluoroelastomer**
* These materials are also compatible for long term (2 months) immersion at elevated
temperature (65°C).
** The WonTMfluorelastomers are marginal for long term (2 months) immersion at
elevated temperature (65°C).
Plastics and elastomers that were found to be unsuitable (U) or marginal (M) for contact
Page 12
with nPB at elevated temperature for short periods (1 5 min.) include:
Plastics
Elastomers
Low density polyethylene (M)
UltemTMpolyether imide (M)
Butyl rubber (M)
NBR nitrile rubber (M)
I
EPDM-60 (U)
Silicone (U)
WOW
- Acute
n-Propyl bromide is toxic, but can be handled safely if reasonable precautions are taken.
Below is a compilation of the current acute toxicology for nPB:
..
m a l i a n Gene- nPB is negative for dominant lethal activity in rats at 400
mg/kg/day given for 5 days to male rats prior to breeding once weekly for 8 successive weeks.
No difference in mating performance was noted in treated males. Their frequency of fertile
matings, mean numbers of corpora lutea, number of implants per female, number of live embryos
per female, and the dominate lethal index was comparable to the negative control group at weeks
1,2,3,4,5,6,7 and 8 after treatment. The frequency of dead implants was higher at week 8 of
treatment compared to the control group, but no increase was observed in the dominate lethal
index at that or any other time. The frequency of dead implants in the treated group was
comparable to the control group at weeks 1,2,3,4,5,6 and 7.
Mammalian M
'
- The half-life of nPB in the rat is very short ( approximately 2
hours). The majority of the administered dose is eliminated rapidly in expired air as the
unchanged parent compound. The remainder is metabolized and excreted in the urine
(predominant route) or in the expired air as C02(minor route).
Following a single intraperitoneal dose (200 mg/kg), the initial rate of excretion of
unchanged (14C)-labeled parent compound in the expired air of the rat was rapid. Two hours
after administration, 56% of the administered dose was exhaled as the parent compound. After 4
hours, 60% had been exhaled: only trace amounts were detected in expired air after this time. An
earlier study also reported the elimination of the unchanged parent compound in expired air.
Oxidation to C 0 2 occurred only to a minor extent. Only 1.4 % of the total dose (or 3.5% of the
metabolized dose) was exhaled as C 0 2 over 48 hours. Approximately 40% of the total IF'administered dose was available for metabolism in the rat and excretion in the urine.
T x'
- The solubility of nPB in is approximately 0.25gllOOml water
at 20 C. The 96 hour LCSO in flathead minnows is 67300 w g L .
Toxicolom - Chronic
Ninety day inhalation studies with rats were used to set the Albemarle Workplace
Exposure Guideline ( A W G ) for workers using nPB on an eight hour shift, five shifts per week.
Page 13
The AWEG has been set at 100 ppm. At this level, solventkleaners based on nPB can be used
safely with modem vapor degreasers and in other applications with proper handling. By
comparison, the exposure guideline (PEL) for trichloroethylene is only 50 ppm (25 ppm in
California).
Environmental and Health Regulatory Status
Worker safety, public safety and environmental protection are paramount in the
development of any new product. The current status of n-propyl bromide and solventhleaner
systems based upon it is:
1. SARA - Supefind Amendments and Re-authorizaton Act. This act requires reporting of
inventories and emissions of listed chemicals and groups. nPB is not regulated.
-
2. HAP Hazardous Air Pollutant. A listing of chemicals that the EPA has declared hazardous.
nPB is not on the list.
3 . NESHAP - National Emission Standard for HAP. Sets standards for use of HAPS.Since nPB
is not a HAP,these standards do not apply.
4. RCRA - Resource Conservation Recovery Act. Defines hazardous wastes and how to
manage them. nPB is not regulated under this act.
5. GWP and HGWP - Global Warming Potential, Atmospheric Lifetime and Ozone Depletion
Potential calculations were carried out in a cooperative effort by Atmospheric and Environmental
Research, Inc. and the Center for Chemical and Environmental Physics at Aerodyne Research,
Inc.' GWP is calculated relative to CO,, while HGWP (Halocarbon GWP) is calculated relative
to CFC-11. GWP calculations were done using different integration time horizons. By the
HGWP method, CFC-11 is ten thousand times more detrimental as a global warming agent than is
nPB. By the GWP method, it is fourteen thousand times worse than nPB, and nPB is only one
tenth as bad as CO,.
ComPoundCFC-11
nPB
1.o
0.0001
GWP
GWP
GaYKSJ
(100 yrs)
4500
1.01
3400
0.31
GWP
(500 yrs)
1400
0.1
6 . Atmospheric Lifetime - Ozone Depletion Potentials (as well as GWP) depend on the
atmospheric lifetime of the substance in question. Ozone depletion takes place in the
stratosphere. In order for a substance to have a high ODP, it must be able to work its way to the
stratosphere. The atmospheric lifetime ofnPB is only eleven days by the latest estimate.' In
comparison, TCA has a lifetime of 5.4 years.
Page 14
7. ODP - Ozone Depletion Potential. Models for calculating ODPs have generally been based on
the assumption that the chemicals are relatively long-lived in the atmosphere. Because of the
short atmospheric lifetime of nPB, certain assumptions had to be made relative to the rate of
transport of the molecules and the free radicals that are formed when they dissociate. In a
recently published paper, two different models were used, resulting in ODPs of 0.0019 and
0.027.4 More recently, Professor Don Wuebbles and associates at the Department of
Atmospheric Sciences, University of Illinois, has determined that the ODP for nPB is only 0.006.5
For comparison, TCA has an ODP of 0.1.
8. PEL - Permissible Exposure Limit. This is the concentration of a material in the air that a
worker can be safely exposed to over a time weighted eight hour work day, five days per week.
Albemarle has set an Albemarle Workplace Exposure Guideline (AWEG) of 100 ppm based on 90
day inhalation tests.
9. VOC - Volatile Organic Compound. All volatile organic compounds are classified as VOCs
until there is experimental evidence that they do not contribute to the formation of smog.
Therefore, nPB is currently classified as a VOC and must be used in accordance with local
regulations regarding VOCs. Studies are currently under way at the Statewide Air Pollution
Research Center, University of California, Riverside, to determine the degree of photo reactivity
of nPB and the types of photochemical products formed. The EPA will review this data to
determine if nPB can be declassified.
10. SNAP - Significant New Alternatives Policy. This is the policy under which EPA gives
approval for the marketing of a replacement for an ozone depleting chemical. ABZOLTM
Cleaners have been commercial since January, 1997, under the EPA S N A P guidelines. The EPA
has indicated in writing that they will soon publish a Proposed Rule in the Federal Register giving
SNAP approval for cleaning, aerosols and emissive solvent uses. A thirty day comment period
will follow before EPA makes the final ruling.
The H&E regulatory status for ABZOLW Cleaners is summarized in Table V.
Summarv
Solvent/Cleaner systems based on n-propyl bromide have been introduced as replacements
for chlorinated solvents in cleaning applications. nPB is an aggressive, fast drying solvent that is
suitable for a variety of difficult cleaning and degreasing applications. The use of nPB based
solvents is not regulated under S A R q HAP, NESHAP or RCRA, and they are approved for sale
under SNAP (further review by EPA possible). nPB has low potentials for ozone depletion and
for global warming, but it is currently classified as a VOC. The Alhemarle Workplace Exposure
Guideline is 100 ppm, which makes it safe to use with the proper precautions for worker safety.
In comparative performance testing, nPB based formulations have been demonstrated to be as
effective as chlorinated solvents and more effective than hydrochlorofluorocarbons,
hydrofluorocarbons, hydrofluorocarbon ethers and volatile methyl siloxanes.
Page 15
I1
1
TABLE V
Environmental and Health Regulatory Status
I
Reeulatlon
SARA
I
ABZOLTMCleaners
1.1.1-Trichloroethane
Trichloroethvlene
No
Yes
Yes
IIHAP
I
No
I
Yes
I
IINESHAP
I
No
I
Yes
I
~
~
No
Yes
Yes
HGWP
0.0001
0.023
Almost Zero?
I
I]Atmospheric Lifetime I
0.0064
11 days'
I
I
1
Yes
RCRA
/I ODP
I1
Yes
0.1
1
Almost Zero?
1
5.4 years
1-
??
1
PEL
IO0 ppm*
350 ppm
50 PPm
voc
Yes
No
Yes
SNAP
Rule to be published
in Federal Register
Unacceptable
Acceptable
1. Electronic Equipment
A company that produces electronic components for clinical equipment used in biomedical
applications had used CFC 113 blends in both liquid and vapor phase defluxing6. Exacting
performance standards, rate of throughput, space limitations, limited capital equipment budget
and lack of an adequate industrial water system were major constraints on a changeover to a new
cleaning system.
The company attempted to switch to a system based on d-limonene. Residue from the
cleaning agent, buildup of rosin flux and reactivity to produce assorted oxidation products made
the electronic components unsuitable for use. An unacceptable green residue remained on the
assemblies and there was an increase in product failures.
M e r switching to a cleaning solvent made from n-propyl bromide (ABZOLTMVG
Cleaner), the company found that the new cleaner did a better job of removing flux than the CFC113 blend. There were no residue problems as there were with d-limonene. Some of the plastic
components did show some discoloration, but this problem was solved by shortening the exposure
Page 16
time -- an added benefit by increasing throughput.
2. Implantable Body Parts
Smith & Nephew Orthopedics (Memphis, TN) manufactures artificial body parts, such as
hip joints, for implantation. The parts consist of a titanium bone replacement and an Ultra High
Molecular Weight Polyethylene W E ) cartilage replacement. Standards for cleanliness are,
of course, very high. In addition, Smith & Nephew expressed concern about retention of solvent
in the UHMWPE parts. A final criteria is that the cleaning solvent must kill at least 50% of the
bacterial spores on an artificially inoculated UHMWPE part. There were two cleaning solvents
that Smith & Nephew wished to replace in their process. The first was based on HCFC-14lb.
The second was based on trichloroethylene.
The initial set of experiments were for part cleanliness, and these were performed at
BaronBlakeslee, Inc. (Long Beach, CA). UHMWPE parts were exposed to ABZ0Lm Cleaner
vapors for 90 seconds. Both cleaned and uncleaned parts were returned to Smith & Nephew,
who found the cleaning to be satisfactory. Acetabular components and hip stems were
contaminated with buffing compound. These were cleaned using the BaronBlakeslee AutoBatch
vapor degreaser. The cycle consisted of 30 seconds in the vapor, 5 minutes immersion in the
ultrasonic sump at 130"F, 2 minutes TopHat drying and 2 minutes freeboard dwell. The parts
were reported to be completely dry with no solvent drag out. BaronBlakeslee returned the parts
to Smith & Nephew, who determined that the cleaning was satisfactory. In a third experiment, a
femoral with finger prints was exposed to vapor for 90 seconds. Evidence of fingerprints
remained after this test.
The second Smith & Nephew concern was retention of the solvent by the UHMWPE
parts. ABZOLTMVG Cleaner was compared directly with commercial cleaning grades of HCFC141b and trichloroethylene. The test procedure was to place five parts in the boiling solvent for
three (3) minutes. The parts were removed and placed in the same solvent at ambient temperature
for two (2) hours. The parts were then removed and placed in an open dish. The dish was left in
a firme hood with the fan going until it was time to take the measurements. To obtain the quantity
of headspace vapors, the parts were placed in a sealed glass chamber and allowed to equilibrate
for one ( I ) hour. The vapors were then analyzed using Gas ChromatographylMass Spectrometry
and quantified against a standard. Measurements were taken at 24 hrs. and 96 hrs. for the
ABZOLTM VG. For the other two solvents, the measurements were at 24 hrs. and 106 hrs The
amount of vapor in the headspace has been converted to ppm by volume.
Concentration of Solvent in H e a w
96 or 106 hrs
ABZOLTMVG
HCFC-14lb
Trichloroethylene
30 PPm
169 ppm
469 ppm
3.7 ppm
4.4 ppm
27 PPm
Page 17
,
These experiments indicate that the AE3ZOLTMVG Cleaner is retained in the UHMWPE parts to a
lesser extent than either the HCFC-141b or the trichloroethylene.
The third criteria was that the solvent/cleaner reduce bacterial spore counts on the
UHMWPE parts by at least 50%. Smith & Nephew supplied two sets of parts (six parts each)
contaminated with SpordexB BuciflusSubiilis (globigii) spores. Each set was divided into two
sets of three parts each -- one set to be cleaned and one set as a control. The cleaning procedure
WaS:
1. Tests parts were placed in the basket of a laboratory vapor degreaser and covered with
a metal screen to prevent the parts from floating to the surface. The degreaser contained
AE3ZOLm VG Cleaner.
2. The basket was lowered into the vapor zone and remained there until condensation
stopped.
3. The basket was then lowered into the boil-up sump (71°C) for 3 minutes (Set A) or
1.5 minutes (Set B).
4. The parts were placed in the rinse sump for 1 min. followed by the vapor zone for 1
min. The basket was allowed to hang in the free board zone for an additional minute to
assure that the parts were dry.
The two sets of cleaned parts along with the accompanying control sets were returned to
Smith & Nephew for analysis. The bioburden validation was done at Axios, Inc. (Kennesaw,
GA). The results were:
.saw!e
Suore Count
Sample A
Control
Cleaned
5.5 x lo6
1.5 x lo6
73%
Sample B
Control
Cleaned
8.8 x lo6
2.8 x lo6
68%
% Reduction
3. Aluminum Parts for Optical Applications
A manufacturer of optical equipment that uses anodized aluminum components. The parts
have lettering and other markings on them. The customer requested an evaluation to make sure
that the markings would not be damaged in the normal cleaning process. They sent four sets of
components, each set containing six different parts. Two sets were cleaned in ABZOLTM VG
.
Page 18
Cleaner by immersing in the boil-up sump for ten minutes followed by one minute in the rinse
sump. The other two sets were immersed for only three minutes in the boil-up sump and then one
minute in the rinse sump. All twenty-four parts were returned to the customer for examination.
No damage to the parts was observed.
4. Electric Motor Stators
The Galley Products Division of B E Aerospace had a need to clean bumt oils from used
electrical motor stators. They sent two such stators for cleaning. One was clean and the other
was covered in oil. Both were cleaned using ABZ0Lm VG Cleaner. They were first lowered
into the vapor zone of a vapor degreaser and held there until condensation of the vapor on the
parts ceased. This required about 5 minutes. They were then lowered into the ultrasonic bath for
ten minutes and back into the vapor zone for 5 minutes. The parts were returned to B E for
examination.
B E Aerospace reported that the parts were “perfect”. No residual oils or other
contaminants were found, and there was no damage to the electrical wiring or casings.
References:
1. Kanegsberg, B., “Precision Cleaning Without Ozone Depleting Chemicals,” Chemistry and
Industry, #20: 787,21, Oct., 1996.
2. Shubkin, R. L., “A New and Effective SolventKleaner with Low Ozone Depletion Potential,”
1996 International Conference on Ozone Protection Technologies, Proceedings and
Presentation, Washington, D. C., October 21-23, 1996.
3. Shubkin, R. L. and Liimatta, E. W., “A New Cleaning Solvent Based on n-Propyl Bromide,’’
NEPCON West ‘97 Conference, Anaheim, CA, February 23-27, 1997.
4. Nelson, D; Wormhoudt, J; Zahniser, M, Kolb, C; KO, M; Weisenstein, D, “On Reaction
Kinetics and Atmospheric Impact of 1-Bromopropane,” The Journal of Physical Chemistry A,
VOI. 101,4987-4990, 1997.
5. Wuebbles, D. J., Jain, A. K., Patten, K. 0. and Connell, P. S., “Evaluation of Ozone
Depletion Potentials for Chlorobromomethane (CH2ClBr) and 1-Bromo-Propane
(CH2BrCH2CH3)”, Atmospheric Environment, in press.
6. Kanegsberg, B., “Cleaning High Value Components for Biomedical and Other Applications,”
1996 International Conference on Ozone Protection Technologies, Proceedings and Presentation,
Washington, D.C., October 21-23, 1996.
.