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Testing of flexible PVC compounds for biostability
I
I
Testing of flexible PVC compounds for biostability
Roger G. Hamel and Thomas C. McEntee of Rohm & Haas compare the performance of three different biocides in protecting PVC films in outdoor applications.
Introduction Laboratory tests, such as ASTM G 21 and Pink Stain test for resistance to Streptoverticillium reticulum are commonly used to demonstrate the effectiveness of biostabilizers for plastic articles. Although these tests are convenient, they do not always give the best comparative indication of performance for outdoor performance. The common zone of inhibition laboratory test depends upon factors such as the rate of diffusion of the biostabilizer to the surface of the plastic, the rate of dissolution from the surface into the aqueous agar phase and the rate of diffusion through the agar phase. Therefore, the test favours faster leaching compounds over slower leaching ones. In practice, however, compounds with lower leach rates may be more effective. Actual exterior exposure tests are more effective at predicting long-term performance. In this article the performance of several biocides are compared:
OBPA OIT DCOIT
10,10-oxybisphenoxarsine 2-n-octyl-isothiazolin-3-one 4,5-dichloro-2-n-octylisothiazolin-3-one These were compared in laboratory and exterior testing and demonstrate the superior performance of D C O I T in protecting flexible PVC films in outdoor applications. Outdoor weathering is expected to give a good indication of real world performance if the material will ultimately be exposed to the elements. Exterior testing is more difficult m do than laboratory testing and requires careful design of the experiment. The reasons include: • The exposure times are usually long. Even in subtropical environments, where the exposure conditions are more challenging, outdoor exposure tests usually require at least one year. • The exact exposure conditions are not controlled. Temperature, rainfall, humidity and sunlight vary from day to day throughout the year and from
Titanium dioxide
w
5.70
19.98
0.57
Lubricants and process aids
0.25
2.05
0.75
0.25
Plastics Additives & Compounding October 2000
24
year to year, so good records of test conditions must be kept. • The choice of location can greatly affect the results of the test, so a consistent testing site is important if one wishes to make comparisons between compounds. The purpose of the study was to report on the performance of DCOIT, a biostabilizer recently introduced in the plastics industry, in exterior performance in the sub-tropical environment. In addition, we compare exterior exposure testing with the more commonly reported laboratory studies of biostability against defined cultures of micro-organisms.
Materials and methods The flexible PVC formulations selected for this study were designed to cover a range of plasticizer (both phthalate and epoxidized soybean oil -ESBO), filler and pigment levels. They were not designed to be specific to any particular application, but to show a range of microbiological response based on our previous knowledge of some of the relationships between formulation variables and microbiological susceptibility. The untreated formulations were all known to be highly susceptible to fungal attack and useful models for the study of biostabilizers. The biostabilizers were added to the formulations, and they were formed into 0.8-mm thick films on a two-roll mill. The films were milled for four minutes at 165°C. The PVC formulations tested included (see Table 1): A A clear flexible PVC formulation with a UV stabilizer
Additives Untreated
r
~
m
o:
:o ,P.,
Blank
B
OBPA
All of the films that did not contain a biostabilizer showed no zone of inhibition against ~ the Stv. reticulum and had trace to moderate stain on the test films. They all developed heavy growth in the ASTM G 21 tests. The unprotected film showed differences in the degree of bio-susceptibility during OIT DCOIT outdoor exposure. Formulation D had a light growth rating in as little as four months while formulation A took nine to ten months to develop the same level of growth.
A moderately pigmented white flexible PVC formulation C A highly pigmented white flexible PVC formulation D A lightly pigmented white flexible PVC formulation with low heat and light stability The biostabilizer levels tested were a blank, 500 ppm OBPA, 1000 and 1200 ppm OIT and 1000 and 1200 ppm DCOIT. In addition, formulations A and B were tested at 800 and 2000 ppm of OIT and 800 and 2000 ppm DCOIT. Portions of each film were subjected to laboratory biostability tests including fungal susceptibility according to the ASTM G 21 test and staining resistance against the pink stain organist Stv. reticulum. The Sub-Tropical Testing Service Site and the Everglades Test Site are located approximately 30 miles South-West of Miami, USA and six miles apart, with the Everglades test site being further inland. The films exposed at the Everglades Test Site consistently develop more severe fungal growth due to higher humidity, less wind and higher rainfall, for example, than at the Sub-Tropical Test Site. The results of the experiments are shown graphically in figures 1-4.
OBPA
treated
All of the OBPA treated film had large zones of inhibition and had no stain in the Pink Stain tests. These four films also developed no growth in the ASTM G 21 tests. The level of mildew protection out-
doors varied with formulation. The films treated with OBPA did not perform as well outdoors as those treated with either of the isothiazolone biostabilizers.
Isothiazolone treated The Pink Stain Tests show very little difference in the performance of the two isothiazolone biostabilizers tested. Above 800 ppm active ingredient, all of the isothiazolone treated film had no stain and the zones of inhibition were comparable for the OIT and DCOIT. DCOIT showed better performance in outdoor weathering due to the too high solubility in water of OIT.
Formulation effects In formulation A, the DCOIT showed consistent good performance outdoors. All of the formulations showed trace growth in the ASTM G 21 tests and all of the films treated with at least 1000 ppm DCOIT showed no stain in the Sty. reticulum tests. In formulation B, the DCOIT showed superior outdoor performance. The OIT showed less performance outdoors but had larger zones of inhibition against the Sty. reticulum. OIT showed a No Growth rating in the ASTM G 21 test at levels of 1000 ppm or higher. In formulation C, the DCOIT showed
~To Growth
Trsce
Growth
Light Growth
Me~lium
Blank
OBPA
OIT
DCOIT
PlasticsAdditives & Compounding October 2000
25
/
Additives 1o m
year, all of the samples had more than medium growth on the samples.
Discussion
Growth Rating at 12 Months
le
e BLANK OBPA OIT
DCOIT
I The moderate to high level of ESBO present in each of the formulas is thought to be the primary intrinsic factor that makes the films susceptible in both laboratory and natural exposure. However, the ESBO alone can not explain higher susceptibility, for example formulation D, in subtropical exposure and failure of the biostabilizer to provide a long term benefit. In order of conventional
i
lo -
-
-
8 -
-
T
-
~
T
T
t
Gm~b Rating at 12 Months
2 ""--m~
0
.
.
""11~
.
~
.
good outdoor performance at one of the outdoor test sites. The D C O I T showed no growth at one site and good performance at the second site. Formulation D was particularly susceptible to fungal attack. At the end of one
-
-
plastic heat and light stability the formulas are thought to rank: C, A, B, and D (best to worst). A previous study (2a) looked at the effect of biocides on the performance of PVC heat stabilizers that showed that the barium zinc stabilizers were compatible with the OBPA and isothiazolone biostabilizers. There were differences in the bio-susceptibility of the various formulations and the performance of the biostabilizers was also found to be formulation dependent. This observation is not surprising and has been observed in many other studies (4,5,6). Table 2 shows some basic data on the biostabilizers. The DCOIT molecule is known to have a slow rate of diffusion to the surface of flexible PVC, which shows good longterm performance under field conditions. However, under optimal conditions for fungal growth in the laboratory the diffusion rate in this formulation may be below its threshold limit or MIC (minimum
Plastics Additives & Compounding October 2000
26
inhibitory concentration) to be effective against all fungi. The ASTM G-21 test was developed to cover a broad group or class of fungi for various polymers. In early years of testing most organisms were isolated on military items, such as textiles and wood, and were used in MIL specifications many years ago. Flexible PVC does not actually support the growth of all of these fungi. In addition, not all of these G-21 organisms have been isolated from flexible PVC and are not necessarily responsible for its deterioration. For example, Aureobasidium has been isolated in many field failures of flexible PVC but fungi such as Chaaetomium and Gliocaldium have not.
Conclusions °
D C O I T showed superior sub-tropical performance compared with OBPA and OIT. In the ASTM G 21, DCOIT treated films typically exhibited Trace Growth compared with Heavy Growth in the untreated formulas. • OBPA showed superior performance in the laboratory tests in all formulations tested. • The commonly employed petri dish tests were not always a good predictor of performance in outdoor applications, but worked well to show the intrinsic susceptibility of formulas. • The level of performance was formulation dependent. The use ofa biostabilizer alone may not ensure the longterm protection of a formulation that is very susceptible to fungal attack and UV degradation. Outdoor test sites, even in the same general geographic area, can confer different severity of exposures. The relative performances of the biostabilizers were consistent between sites. Subtropical exposure is expected to accelerate the fungal growth on the samples, but should reflect the same relative performance in milder climates outdoors.
References I.
Renate Borgmann-Strahsen and Malcolm T. J. Mellor, "Activity of Fungistatic Agents in PVC-P",
Additives Table 2: Physical properties of biostabilizers Biostabilizer (ppm)
Melting point (°C)
DCOIT
Water solubility
[84-1:86
5
20
480
40-41
2
OIT
Kunststoffe 89 (1999) 7, pp. 68-74. 2(a). R. G. Hamel and N. M. Rei, "The Effect of Biocide Selection on the Performance of PVC Heat Stabilizers", Society of Plastics Engineers, ANTEC (1993), p. 2963-2976. 2(b). R. Borgaman-Strahsen and E. Bessems, "Influence of Stabilizers and Production Procedure on the Effectivity of Fungistats in Flexible PVC", Journal of Coated Fabrics, 23 91994), p. 221-227. 2(c). Wolfgang Linger, Technical Secretary, IBRG, Document No.:
3.
of Plasticised PVC" Society of Plastics Engineers, (1970), p. 26-30. This article is a summary of a paper presented at the AddPlast Europe 2000 conference.
Contact:
IBRG/PPG/9703. N.M. Rei, T. C. McEntee and J. Brophy, "Fungicides and Biocides", Plastics Additives and Modifiers Handbook, Jesse Edenbaum, ed. New
4. 5.
6.
York: Van Norstrand Reinhold, 1992. H. Becker and H. Gross, Materials and Organisms 9 (1974), p. 81-131. K.J. Seal, "The Biodeterioration and Biodegradation of Naturally Occurring and Synthetic Plastic Polymers", Biodeter-ioration Abstracts 2 (1988) 4. P 295-317. G. Tirpak "Microbial Degradation
Non-halogenated flame reta with a price-performance aq
Rohm and Haas Company, 185 rue de Bercy, 75579 Paris, Cedex 12, France Tel: + 33 1 4002 5000 Fax." + 33 1 4345 2819 Rohm and Haas Company, 1 O0 Independence Mall West, Philadelphia, PA 19106-2399, USA Tel: +1 215-592-3000 Fax: +1 215-592-3377
nce e!
!~:~!i~i!i
MagShield* advantages: • Priced competitively to A T H • H i g h e r t h e r m a l process stability t h ~ A T H • N o n - t o x i c an d N o n - c o r r osi ve .............................. tAX: 410-7S0-57~
www.magspecialtles.com e-mail: ~v|a~chem~i
PLEASE INSERT 009 ON READER ENQUIRY CARD
PlasticsAdditives & Compounding October 2000
27
I
Testing of flexible PVC compounds for biostability
Roger G. Hamel and Thomas C. McEntee of Rohm & Haas compare the performance of three different biocides in protecting PVC films in outdoor applications.
Introduction Laboratory tests, such as ASTM G 21 and Pink Stain test for resistance to Streptoverticillium reticulum are commonly used to demonstrate the effectiveness of biostabilizers for plastic articles. Although these tests are convenient, they do not always give the best comparative indication of performance for outdoor performance. The common zone of inhibition laboratory test depends upon factors such as the rate of diffusion of the biostabilizer to the surface of the plastic, the rate of dissolution from the surface into the aqueous agar phase and the rate of diffusion through the agar phase. Therefore, the test favours faster leaching compounds over slower leaching ones. In practice, however, compounds with lower leach rates may be more effective. Actual exterior exposure tests are more effective at predicting long-term performance. In this article the performance of several biocides are compared:
OBPA OIT DCOIT
10,10-oxybisphenoxarsine 2-n-octyl-isothiazolin-3-one 4,5-dichloro-2-n-octylisothiazolin-3-one These were compared in laboratory and exterior testing and demonstrate the superior performance of D C O I T in protecting flexible PVC films in outdoor applications. Outdoor weathering is expected to give a good indication of real world performance if the material will ultimately be exposed to the elements. Exterior testing is more difficult m do than laboratory testing and requires careful design of the experiment. The reasons include: • The exposure times are usually long. Even in subtropical environments, where the exposure conditions are more challenging, outdoor exposure tests usually require at least one year. • The exact exposure conditions are not controlled. Temperature, rainfall, humidity and sunlight vary from day to day throughout the year and from
Titanium dioxide
w
5.70
19.98
0.57
Lubricants and process aids
0.25
2.05
0.75
0.25
Plastics Additives & Compounding October 2000
24
year to year, so good records of test conditions must be kept. • The choice of location can greatly affect the results of the test, so a consistent testing site is important if one wishes to make comparisons between compounds. The purpose of the study was to report on the performance of DCOIT, a biostabilizer recently introduced in the plastics industry, in exterior performance in the sub-tropical environment. In addition, we compare exterior exposure testing with the more commonly reported laboratory studies of biostability against defined cultures of micro-organisms.
Materials and methods The flexible PVC formulations selected for this study were designed to cover a range of plasticizer (both phthalate and epoxidized soybean oil -ESBO), filler and pigment levels. They were not designed to be specific to any particular application, but to show a range of microbiological response based on our previous knowledge of some of the relationships between formulation variables and microbiological susceptibility. The untreated formulations were all known to be highly susceptible to fungal attack and useful models for the study of biostabilizers. The biostabilizers were added to the formulations, and they were formed into 0.8-mm thick films on a two-roll mill. The films were milled for four minutes at 165°C. The PVC formulations tested included (see Table 1): A A clear flexible PVC formulation with a UV stabilizer
Additives Untreated
r
~
m
o:
:o ,P.,
Blank
B
OBPA
All of the films that did not contain a biostabilizer showed no zone of inhibition against ~ the Stv. reticulum and had trace to moderate stain on the test films. They all developed heavy growth in the ASTM G 21 tests. The unprotected film showed differences in the degree of bio-susceptibility during OIT DCOIT outdoor exposure. Formulation D had a light growth rating in as little as four months while formulation A took nine to ten months to develop the same level of growth.
A moderately pigmented white flexible PVC formulation C A highly pigmented white flexible PVC formulation D A lightly pigmented white flexible PVC formulation with low heat and light stability The biostabilizer levels tested were a blank, 500 ppm OBPA, 1000 and 1200 ppm OIT and 1000 and 1200 ppm DCOIT. In addition, formulations A and B were tested at 800 and 2000 ppm of OIT and 800 and 2000 ppm DCOIT. Portions of each film were subjected to laboratory biostability tests including fungal susceptibility according to the ASTM G 21 test and staining resistance against the pink stain organist Stv. reticulum. The Sub-Tropical Testing Service Site and the Everglades Test Site are located approximately 30 miles South-West of Miami, USA and six miles apart, with the Everglades test site being further inland. The films exposed at the Everglades Test Site consistently develop more severe fungal growth due to higher humidity, less wind and higher rainfall, for example, than at the Sub-Tropical Test Site. The results of the experiments are shown graphically in figures 1-4.
OBPA
treated
All of the OBPA treated film had large zones of inhibition and had no stain in the Pink Stain tests. These four films also developed no growth in the ASTM G 21 tests. The level of mildew protection out-
doors varied with formulation. The films treated with OBPA did not perform as well outdoors as those treated with either of the isothiazolone biostabilizers.
Isothiazolone treated The Pink Stain Tests show very little difference in the performance of the two isothiazolone biostabilizers tested. Above 800 ppm active ingredient, all of the isothiazolone treated film had no stain and the zones of inhibition were comparable for the OIT and DCOIT. DCOIT showed better performance in outdoor weathering due to the too high solubility in water of OIT.
Formulation effects In formulation A, the DCOIT showed consistent good performance outdoors. All of the formulations showed trace growth in the ASTM G 21 tests and all of the films treated with at least 1000 ppm DCOIT showed no stain in the Sty. reticulum tests. In formulation B, the DCOIT showed superior outdoor performance. The OIT showed less performance outdoors but had larger zones of inhibition against the Sty. reticulum. OIT showed a No Growth rating in the ASTM G 21 test at levels of 1000 ppm or higher. In formulation C, the DCOIT showed
~To Growth
Trsce
Growth
Light Growth
Me~lium
Blank
OBPA
OIT
DCOIT
PlasticsAdditives & Compounding October 2000
25
/
Additives 1o m
year, all of the samples had more than medium growth on the samples.
Discussion
Growth Rating at 12 Months
le
e BLANK OBPA OIT
DCOIT
I The moderate to high level of ESBO present in each of the formulas is thought to be the primary intrinsic factor that makes the films susceptible in both laboratory and natural exposure. However, the ESBO alone can not explain higher susceptibility, for example formulation D, in subtropical exposure and failure of the biostabilizer to provide a long term benefit. In order of conventional
i
lo -
-
-
8 -
-
T
-
~
T
T
t
Gm~b Rating at 12 Months
2 ""--m~
0
.
.
""11~
.
~
.
good outdoor performance at one of the outdoor test sites. The D C O I T showed no growth at one site and good performance at the second site. Formulation D was particularly susceptible to fungal attack. At the end of one
-
-
plastic heat and light stability the formulas are thought to rank: C, A, B, and D (best to worst). A previous study (2a) looked at the effect of biocides on the performance of PVC heat stabilizers that showed that the barium zinc stabilizers were compatible with the OBPA and isothiazolone biostabilizers. There were differences in the bio-susceptibility of the various formulations and the performance of the biostabilizers was also found to be formulation dependent. This observation is not surprising and has been observed in many other studies (4,5,6). Table 2 shows some basic data on the biostabilizers. The DCOIT molecule is known to have a slow rate of diffusion to the surface of flexible PVC, which shows good longterm performance under field conditions. However, under optimal conditions for fungal growth in the laboratory the diffusion rate in this formulation may be below its threshold limit or MIC (minimum
Plastics Additives & Compounding October 2000
26
inhibitory concentration) to be effective against all fungi. The ASTM G-21 test was developed to cover a broad group or class of fungi for various polymers. In early years of testing most organisms were isolated on military items, such as textiles and wood, and were used in MIL specifications many years ago. Flexible PVC does not actually support the growth of all of these fungi. In addition, not all of these G-21 organisms have been isolated from flexible PVC and are not necessarily responsible for its deterioration. For example, Aureobasidium has been isolated in many field failures of flexible PVC but fungi such as Chaaetomium and Gliocaldium have not.
Conclusions °
D C O I T showed superior sub-tropical performance compared with OBPA and OIT. In the ASTM G 21, DCOIT treated films typically exhibited Trace Growth compared with Heavy Growth in the untreated formulas. • OBPA showed superior performance in the laboratory tests in all formulations tested. • The commonly employed petri dish tests were not always a good predictor of performance in outdoor applications, but worked well to show the intrinsic susceptibility of formulas. • The level of performance was formulation dependent. The use ofa biostabilizer alone may not ensure the longterm protection of a formulation that is very susceptible to fungal attack and UV degradation. Outdoor test sites, even in the same general geographic area, can confer different severity of exposures. The relative performances of the biostabilizers were consistent between sites. Subtropical exposure is expected to accelerate the fungal growth on the samples, but should reflect the same relative performance in milder climates outdoors.
References I.
Renate Borgmann-Strahsen and Malcolm T. J. Mellor, "Activity of Fungistatic Agents in PVC-P",
Additives Table 2: Physical properties of biostabilizers Biostabilizer (ppm)
Melting point (°C)
DCOIT
Water solubility
[84-1:86
5
20
480
40-41
2
OIT
Kunststoffe 89 (1999) 7, pp. 68-74. 2(a). R. G. Hamel and N. M. Rei, "The Effect of Biocide Selection on the Performance of PVC Heat Stabilizers", Society of Plastics Engineers, ANTEC (1993), p. 2963-2976. 2(b). R. Borgaman-Strahsen and E. Bessems, "Influence of Stabilizers and Production Procedure on the Effectivity of Fungistats in Flexible PVC", Journal of Coated Fabrics, 23 91994), p. 221-227. 2(c). Wolfgang Linger, Technical Secretary, IBRG, Document No.:
3.
of Plasticised PVC" Society of Plastics Engineers, (1970), p. 26-30. This article is a summary of a paper presented at the AddPlast Europe 2000 conference.
Contact:
IBRG/PPG/9703. N.M. Rei, T. C. McEntee and J. Brophy, "Fungicides and Biocides", Plastics Additives and Modifiers Handbook, Jesse Edenbaum, ed. New
4. 5.
6.
York: Van Norstrand Reinhold, 1992. H. Becker and H. Gross, Materials and Organisms 9 (1974), p. 81-131. K.J. Seal, "The Biodeterioration and Biodegradation of Naturally Occurring and Synthetic Plastic Polymers", Biodeter-ioration Abstracts 2 (1988) 4. P 295-317. G. Tirpak "Microbial Degradation
Non-halogenated flame reta with a price-performance aq
Rohm and Haas Company, 185 rue de Bercy, 75579 Paris, Cedex 12, France Tel: + 33 1 4002 5000 Fax." + 33 1 4345 2819 Rohm and Haas Company, 1 O0 Independence Mall West, Philadelphia, PA 19106-2399, USA Tel: +1 215-592-3000 Fax: +1 215-592-3377
nce e!
!~:~!i~i!i
MagShield* advantages: • Priced competitively to A T H • H i g h e r t h e r m a l process stability t h ~ A T H • N o n - t o x i c an d N o n - c o r r osi ve .............................. tAX: 410-7S0-57~
www.magspecialtles.com e-mail: ~v|a~chem~i
PLEASE INSERT 009 ON READER ENQUIRY CARD
PlasticsAdditives & Compounding October 2000
27