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Renewable Resource, Sustainable and Biodegradable Polymers
13 Renewable Resource, Sustainable and Biodegradable Polymers The polymers covered in this chapter are those that are produced from renewable resource raw materials, such as corn or that are biodegradable or compostable. Biopolymers are materials that either occur naturally (i.e., proteins, sugars) or are synthesized from naturally occurring biological materials like sugars, fats, oil, and starch and these are included in this chapter. This is a developing area in packaging materials and medical products and though there are a relatively limited number of polymers used commercially, they will certainly become more numerous and more common in the future. Biodegradable plastics are made out of ingredients that can be metabolized by naturally occurring microorganisms in the environment. Some petroleum-based plastics will biodegrade eventually, but that process usually takes a very long time and contributes to global warming through the release of carbon dioxide. The ASTM D6400-04 standard specification for compostable plastics has definitions for various types of degradable plastics which are as follows:
• Degradable plastics are designed to undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties that may vary as measured by standard test methods appropriate to the plastic and the application in a period of time that determines its classification.
• Biodegradable plastics are plastics in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi, and algae.
• Photodegradable plastics are plastics in which the degradation results from the action of natural daylight.
• Oxidatively degradable plastics are degradable plastics in which the degradation results from oxidation.
• Hydrolytically degradable plastics are degradable plastics in which the degradation results from hydrolysis.
• Compostable plastics are plastics that undergo degradation by biological processes during composting to yield carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials. They leave no visually distinguishable or toxic residue. Renewable plastic is derived from natural plant products such as corn, oats, wood, and other plants, which helps ensure the sustainability of the earth. Polylactic acid (PLA) is the most widely researched and used 100% biodegradable plastic packaging polymer currently and is made entirely from corn-based cornstarch. Details on PLA are included in a following section. Interest in these materials is strong as the number of commercially available materials grows. However, many materials are not commercially viable and disappear. The table of trade names and producers from the previous edition has been removed for this reason. Trade names and Producers are listed in the individual sections for each polymer. Weather resistance and ultraviolet (UV) resistance is not usually a desired property for those polymers which are compostable or biodegradable. However, some data are available as the rate of decomposition is used to calculate or estimate the lifetime or breakdown rates. For these materials, water is critical to decomposition. Renewable resourced polymers may need weather and UV resistance as their aim is to not use oil-based raw materials. The following sections contain the details of several of the more common sustainable polymers.
13.1 Cellulose-Based Materials Cellulose is an organic compound with the formula (C6H10O5)n the structure of which is shown in
The Effect of UV Light and Weather on Plastics and Elastomers. DOI: https://doi.org/10.1016/B978-0-12-816457-0.00013-7 © 2019 Elsevier Inc. All rights reserved.
425
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Figure 13.1 Chemical structure of cellulose.
Figure 13.2 UV degradation in cellulose. UV, Ultraviolet.
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Fig. 13.1. It is a polysaccharide consisting of a linear chain of several hundred to over ten thousand linked D-glucose units. Cellulose is mainly obtained from wood pulp and cotton. Cellulose is chemically modified to make many polymers that are useful in plastics or coatings. Some of these modifications are described in subsequent sections. Cellulose-based plastics are generally biodegradable and they are degraded by UV. Chain scission and various radicals can be produced as shown in Fig. 13.2. The macroradicals can react with oxygen producing hydroperoxide and other decomposition products as is common in many of the other
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plastics. In spite of these reaction possibilities, cellulose is a relatively stable material.
13.1.1 Cellophane Cellophane is a polymeric cellulose film made from the cellulose from wood, cotton, hemp, or other sources. The raw material of choice is called dissolving pulp, which is white like cotton and contains 92%98% cellulose. The cellulose is dissolved in alkali in a process known as mercerization. It is aged several days. The mercerized pulp is treated with carbon disulfide to make an orange solution called viscose or cellulose xanthate. The viscose solution is then extruded through a slit into a bath of dilute sulfuric acid and sodium sulfate to reconvert the viscose into cellulose. The film is then passed through several more baths, one to remove sulfur, one to bleach the film, and one to add glycerin to prevent the film from becoming brittle. Cellophane has a CAS number of 9005-81-6. The approximate chemical structures are shown in Fig. 13.3. The Cellophane may be coated with nitrocellulose or wax to make it impermeable to water vapor. It may also be coated with polyethylene or other materials to make it heat sealable for automated wrapping machines. Weathering Viscose is largely transparent to UV light, but prolonged exposure to sunlight weakens viscose rayon fibers. A 6-hour exposure of unstabilized viscose to UV light leads to a loss in in strength of about 4% [1]. Manufacturers Cellophane
and
trade
names:
Innovia
Figure 13.3 Conversion of raw cellulose to viscose.
427
Applications and uses: Cellulosic film applications include tapes and labels, photographic film, coatings for paper, glass, and plastic, fibers for clothing Data for cellophane/viscose polymers are found in Fig. 13.4.
13.1.2 Nitrocellulose Nitrocellulose is made by treating cellulose with a mixture of sulfuric and nitric acids. This changes the hydroxyl groups (2OH) on the cellulose to nitro groups (2NO3) as shown in Fig. 13.5. Nitrocellulose, also known as gun cotton and is the main ingredient of smokeless gunpowder, decomposes explosively. In the early 20th century, it was found to make an excellent film and paint. Nitrocellulose lacquer was used as a finish on guitars and saxophones for most of the 20th century and is still used on some current applications. Manufactured by (among others) DuPont, the paint was also used on automobiles sharing the same color codes as many guitars including Fender and Gibson brands. Nitrocellulose lacquer is also used as an aircraft dope, painted onto fabric-covered aircraft to tauten and provide protection to the material. Its CAS number is 9004-70-0. Nitrocellulose is not molded. It has been used in coatings and was widely used as automotive paint in the 1930s. The early types of nitrocellulose automotive lacquers showed signs of deterioration after a few months’ exposure in Florida. 2-(20 Hydroxy-30 ,50 -di-tert-butylphenyl)-5-chlorobenzotriazole (e.g., Tinuvin 327) is highly effective in stabilizing nitrocellulose coatings at a use level range of 0.5%2.0% and can be used in combination with phenolic and phosphate antioxidants, as
428
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Figure 13.4 Effect of irradiation with UV light on the tensile strength retention of unstabilized viscose rayon to that stabilized with the sulfuric acid ester of 4-fl-hydroxyethylsulfonyl-2-aminoanisole [2]. UV, Ultraviolet. Table 13.1 Yellowness Index of Nitrocellulose in a Wood Coating Before and After 24 h Exposure to QUV-B 313 (UVB-313 Lamps Produce not only the Shortest Ultraviolet Rays that the Sun Emits, they Also Emit Unnaturally, Short-wavelengths Below What is Found on the Earth’s Surface) [3] Hours exposed
0
24
Yellowness index of nitrocellulose without UV stabilizer
1.0
18.3
Yellowness index of nitrocellulose with UV stabilizer
0.7
15.9
UV, Ultraviolet.
Figure 13.5 Structure of nitrocellulose.
well as hindered amine light stabilizers (HALS), to optimize performance in outdoor applications. Nitrocellulose is not usually used by itself for film applications, but more commonly is part of multilayered films structures, especially those based on cellophane. Manufacturers and trade names: Innovia Films Cellophane Applications and uses: Food wrap, coatings (for guitars) Data for nitrocellulose is found in Table 13.1.
13.1.3 Cellulose Acetate Cellulose acetate is the acetate ester of cellulose. It is sometimes called acetylated cellulose or xylonite. Its CAS number is 9004-35-7 and the approximate chemical structure is shown in Fig. 13.6. Cellulose acetate weathers well and is nonyellowing on long-term exposure to the sun, making it useful as a coating for signs and decals. The transparency of CA coatings and their ability to transmit sunlight, particularly beneficial UV rays, have led to extensive use of these film formers for coating wire screening for greenhouse windows, poultry runs, and similar structures. The good physical strength of the coatings yields a tough, tear-resistant screen [4].
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429
Manufacturers and trade names: Celanese Cellulose Acetate; Eastman Chemical Company Tenite; Daicel Corporation; Solvay Ocalio; Rotuba Applications and uses: Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters, found in screwdriver handles, ink pen reservoirs, and X-ray films Data for cellulose acetate is in Table 13.2.
13.1.4 Cellulose Acetate Butyrate
Figure 13.6 Chemical structure of cellulose acetate.
Cellulose acetate butyrate (CAB) is a mixed ester of cellulose. CAB, commonly known as butyrate, is resistant to UV rays, has lower moisture absorption than cellulose acetate and has extremely high impact strength. Its CAS number is 9004-36-8 and the approximate chemical structure is shown in Fig. 13.7.
Table 13.2 Remaining Weight of Samples of Cellulose Acetate With Various Plasticizers After Being Subjected to QUV Test Machine With Water Spray Accelerated Weathering Testing [5] Sample
Accelerated Weathering Time (h) 0
125
175
325
425
% Remaining weight Pure cellulose acetate
100
100
98
98
100
With 20 wt% polyethylene glycol
100
92
89
81
80
With 20 wt% triacetin
100
100
100
95
94
With 20 wt% tripropionin
100
100
100
94
87
With 20 wt% triethyl citrate
100
98
95
96
94
Figure 13.7 Chemical structure of cellulose acetate butyrate.
430
Manufacturers and trade names: Chemical Company Tenite; Uvex; Spartech
THE EFFECT
Eastman Excelon,
Applications and uses: Printing visual aids, page protection and animation cells Data for CAB polymers are found in Figs. 13.813.10.
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13.1.5 Ethyl Cellulose Ethyl cellulose is similar in structure to cellulose and cellulose acetate, but some of the hydroxyl (2OH) functional groups are replaced on the cellulose by the ethoxy group (OCH2CH3). Ethyl cellulose has a CAS number of 9004-57-3 and its structure is shown in Fig. 13.11.
Figure 13.8 Tensile strength at break after Arizona Weathering for Eastman Tenite Butyrate [2]. Note: 3.2-mm (0.125-in.) thick specimens of an outdoor type of Tenite butyrate [14].
Figure 13.9 Elongation at break after Arizona Weathering for Eastman Tenite Butyrate [2]. Note: 3.2-mm (0.125-in.) thick specimens of an outdoor type of Tenite butyrate.
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431
Figure 13.10 Impact strength after weathering for Eastman Tenite Butyrate [2]. Note: 3.2-mm (0.125-in.) thick specimens of an outdoor type of Tenite butyrate; samples weathered in a vertical position facing due south. Testing as per ASTM D3029.
Dow Ethocel does not discolor on exposure to strong sunlight nor does it promote the discoloration of plasticizers or polymers [6].
13.2 Polycaprolactone
Figure 13.11 Structure of ethyl cellulose.
Several phenolic stabilizers may be used with ethyl cellulose. Manufacturers and trade names: Dow Ethocel, Ashland Aqualon Applications and uses: Pharmaceutical applications, cosmetics, nail polish, vitamin coatings, printing inks, specialty coatings, and food packaging
Polycaprolactone (PCL) is biodegradable polyester with a low melting point of around 60°C and a glass transition temperature of about 260°C. PCL is prepared by ring opening polymerization of ε-caprolactone using a catalyst such as stannous octanoate. The structure of caprolactone and PCL is shown in Fig. 13.12. PCL is degraded by hydrolysis of its ester linkages in physiological conditions (such as in the human body) and has therefore received a great deal of attention for use as an implantable biomaterial. In particular, it is especially interesting for the preparation of long term implantable devices. A variety of drugs have been encapsulated within PCL beads for controlled release and targeted drug delivery. PCL is often mixed with starch to obtain a good biodegradable material at a low price. Perstorp offers PCLs under the trade name CAPAt. Low molecular weight PCLs may be added to other plastics to improve their weather resistance.
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Figure 13.12 Conversion of caprolactone to polycaprolactone.
Figure 13.13 Conversion of lactic acid to polylactic acid by two routes.
Manufacturers and trade names: Perstorp CAPA (previously Solvay), Dow Chemical Tone (discontinued) Applications and uses: The mix of PCL and starch has been successfully used for making trash bags in Korea (Yukong Company)
13.3 Poly(lactic acid) PLA is derived from renewable resources, such as cornstarch or sugarcanes. PLA polymers are considered biodegradable and compostable. PLA is a thermoplastic, high-strength, high-modulus polymer that can be made from annually renewable sources to yield articles for use in either the
industrial packaging field or the biocompatible/ bioabsorbable medical device market. Bacterial fermentation is used to make lactic acid, which is then converted to the lactide dimer to remove the water molecule which would otherwise limit the ability to make high molecular weight polymer. The lactide dimer, after the water is removed, can be polymerized without the production of the water. This process is shown in Fig. 13.13 and can proceed by two possible routes, the direct route and the lactide route. The PLA CAS number is 9002-97-5. Manufacturers and trade names: FKur Bio-Flex, Cereplast Inc. Compostables, Mitsubishi Chemical Fozeas, NatureWorks LLC Ingeo, Alcan Packaging Ceramis-PLA
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Applications and uses: Biomedical applications, such as sutures, stents, dialysis media, and drug delivery devices. It is also being evaluated as a material for tissue engineering, loose-fill packaging, compost bags, food packaging, and disposable tableware. PLA can be in the form of fibers and nonwoven textiles; potential uses: upholstery, disposable garments, awnings, and feminine hygiene products Data for PLA is shown in Figs. 13.1413.20.
433
13.4 Poly-3-hydroxybutyrate Polyhydroxyalkanoates (PHAs) are naturally produced and include poly-3-hydroxybutyrate (PHB or PH3B), polyhydroxyvalerate and polyhydroxyhexanoate; A PHA copolymer called PHBV (PHB-co3-hydroxyvalerate) is less stiff and tougher, and it may be used as packaging material. Chemical structures of some of these polymers are shown in Fig. 13.21.
Figure 13.14 Tensile strength of poly(lactic acid) and polylactide during a weather ability test (accelerated test using a Weather-Ometer) [7].
Figure 13.15 Tensile strength of poly(lactic acid) and polylactide during an outdoor exposure test [7].
Figure 13.16 Ball Burst strength vs UV exposure time of Ingeo PLA fabric [8]. Note: Test Method: ASTM D3787; ATTCC 16E light exposure. UV, Ultraviolet; PLA, Polylactic acid.
Figure 13.17 Molecular weight loss vs UV exposure time of Ingeo PLA fabric [8]. Note: ATTCC 16E Light exposure. UV, Ultraviolet; PLA, Polylactic acid.
Figure 13.18 Color change vs UV exposure time of Ingeo PLA fabric [8]. Note: ATTCC 16E light exposure; HunterLab D65/10° Illuminator/observer. UV, Ultraviolet.
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435
Figure 13.19 Number average molecular weight dependence on ageing time at 50°C with and without. UV exposure and humidity of flame retarded PLA [9]. Note: Humidity tests using Memmert Humidity Chamber Model HCP 108, UV using a Q-LAB QUV chamber with and without water spray. UV, Ultraviolet; PLA, Polylactic acid.
Figure 13.20 Melting Tm dependence on ageing time at 50°C with and without UV exposure and humidity of flame retarded PLA. [9]. Note: Humidity tests using HCP 108 device, UV using a Q-LAB QUV chamber with and without water spray. Tm, Temperature; UV, Ultraviolet; PLA, Polylactic acid.
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Figure 13.21 Structures of several polyhydroxyalkanoates.
Figure 13.22 Tensile strength vs accelerated weathering exposure time of PHBV [10]. Note: Xenon-arc Weather-Ometer (Q-Sun Xe-1-S). The films were exposed to a repeated 2 h cycle of radiation followed by 2 h of radiation plus water spray. PHBV, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).
Articles made of PHB thermoplasts retain their original shape at 121 or 132°C. Because of this, perishable goods can be canned into packages produced of Biomer resins and preserved by steam sterilization.
Chemical Fozeas, NatureWorks LLC Ingeo, Alcan Packaging Ceramis-PLA, Metabolix/ ADM Tirel, Tianan Enmat, Copersucar Biocycle, Biomer Biomer L, Procter & Gamble Nodax
Manufacturers and trade names: FKur BioFlex, Cereplast Inc. Compostables, Mitsubishi
Applications and uses: Biomedical applications, such as sutures, stents, dialysis media, and drug
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437
Figure 13.23 Young’s modulus vs accelerated weathering exposure time of PHBV [10]. Note: Xenon-arc Weather-Ometer (Q-Sun Xe-1-S). The films were exposed to a repeated 2 h cycle of radiation followed by 2 h of radiation plus water spray. PHBV, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).
Figure 13.24 Elongation at break vs accelerated weathering exposure time of PHBV [10]. Note: Xenon-arc Weather-Ometer (Q-Sun Xe-1-S). The films were exposed to a repeated 2 h cycle of radiation followed by 2 h of radiation plus water spray. PHBV, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).
delivery devices. It is also being evaluated as a material for tissue engineering, loose-fill packaging, compost bags, food packaging, and disposable tableware. PLA can be in the form of fibers and nonwoven textiles; potential uses: upholstery, disposable garments, awnings, and feminine hygiene products Data for PHB plastics are found in Figs. 13.2213.24.
References [1] C. Panchigar, Compiled From Various Sources. Available from: https://www.scribd.com/doc/ 48749674/Property-of-Viscose. [2] T.B. Boboev, K.M. Makhkamov, B.N. Narzullaev, et al., Polymer Mechanics 10 (1974) 791. Available from: https://doi.org/ 10.1007/BF00857967.
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[3] Eastman Chemical Company, Eastmant Cellulose Ester Technical Tip, Controlling Yellowing in Wood Coatings, Eastman Chemical Company, 2013. [4] Eastman Chemical Company, Eastmant Cellulose-Based Specialty Polymers, Eastman Chemical Company, 2009. [5] R. Quintana, O. Persenaire, Y. Lemmouchi, J. Sampson, S. Martin, L. Bonnaud, et al., Enhancement of cellulose acetate degradation under accelerated weathering by plasticization with eco-friendly plasticizers, Polym. Degrad. Stab. 98 (9) (2013) 15561562. Available from: https://doi.org/10.1016/j.polymdegradstab. 2013.06.032. [6] Dow Chemical Company, ETHOCEL Ethylcellulose Polymers Technical Handbook, Dow Chemical Company, 2005. [7] M. Ajioka, K. Enomoto, K. Suzuki, A. Yamaguchi, The basic properties of poly
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(lactic acid) produced by the direct condensation polymerization of lactic acid, J. Environ. Polym. Degrad. 3 (1995) 225234. [8] Ingeo, NatureWorks LLC, UV Resistance, Technical Bulletin 370904, Ingeo, NatureWorks LLC, 2006. [9] N. Lesaffre, S. Bellayer, H. Vezin, G. Fontaine, M. Jimenez, S. Bourbigot, Recent advances on the ageing of flame retarded PLA: effect of UV-light and/or relative humidity, Polym. Degrad. Stab. 139 (2017) 143164. Available from: https://doi.org/ 10.1016/j.polymdegradstab.2017.04.007. [10] L. Wei, A.G. McDonald, Accelerated weathering studies on the bioplastic, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), Polym. Degrad. Stab. 126 (2016) 93100. Available from: https://doi.org/10.1016/j.polymdegradstab. 2016.01.023.
• Degradable plastics are designed to undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties that may vary as measured by standard test methods appropriate to the plastic and the application in a period of time that determines its classification.
• Biodegradable plastics are plastics in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi, and algae.
• Photodegradable plastics are plastics in which the degradation results from the action of natural daylight.
• Oxidatively degradable plastics are degradable plastics in which the degradation results from oxidation.
• Hydrolytically degradable plastics are degradable plastics in which the degradation results from hydrolysis.
• Compostable plastics are plastics that undergo degradation by biological processes during composting to yield carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials. They leave no visually distinguishable or toxic residue. Renewable plastic is derived from natural plant products such as corn, oats, wood, and other plants, which helps ensure the sustainability of the earth. Polylactic acid (PLA) is the most widely researched and used 100% biodegradable plastic packaging polymer currently and is made entirely from corn-based cornstarch. Details on PLA are included in a following section. Interest in these materials is strong as the number of commercially available materials grows. However, many materials are not commercially viable and disappear. The table of trade names and producers from the previous edition has been removed for this reason. Trade names and Producers are listed in the individual sections for each polymer. Weather resistance and ultraviolet (UV) resistance is not usually a desired property for those polymers which are compostable or biodegradable. However, some data are available as the rate of decomposition is used to calculate or estimate the lifetime or breakdown rates. For these materials, water is critical to decomposition. Renewable resourced polymers may need weather and UV resistance as their aim is to not use oil-based raw materials. The following sections contain the details of several of the more common sustainable polymers.
13.1 Cellulose-Based Materials Cellulose is an organic compound with the formula (C6H10O5)n the structure of which is shown in
The Effect of UV Light and Weather on Plastics and Elastomers. DOI: https://doi.org/10.1016/B978-0-12-816457-0.00013-7 © 2019 Elsevier Inc. All rights reserved.
425
426
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OF
Figure 13.1 Chemical structure of cellulose.
Figure 13.2 UV degradation in cellulose. UV, Ultraviolet.
UV LIGHT
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WEATHER
ON
PLASTICS
AND
ELASTOMERS
Fig. 13.1. It is a polysaccharide consisting of a linear chain of several hundred to over ten thousand linked D-glucose units. Cellulose is mainly obtained from wood pulp and cotton. Cellulose is chemically modified to make many polymers that are useful in plastics or coatings. Some of these modifications are described in subsequent sections. Cellulose-based plastics are generally biodegradable and they are degraded by UV. Chain scission and various radicals can be produced as shown in Fig. 13.2. The macroradicals can react with oxygen producing hydroperoxide and other decomposition products as is common in many of the other
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BIODEGRADABLE POLYMERS
plastics. In spite of these reaction possibilities, cellulose is a relatively stable material.
13.1.1 Cellophane Cellophane is a polymeric cellulose film made from the cellulose from wood, cotton, hemp, or other sources. The raw material of choice is called dissolving pulp, which is white like cotton and contains 92%98% cellulose. The cellulose is dissolved in alkali in a process known as mercerization. It is aged several days. The mercerized pulp is treated with carbon disulfide to make an orange solution called viscose or cellulose xanthate. The viscose solution is then extruded through a slit into a bath of dilute sulfuric acid and sodium sulfate to reconvert the viscose into cellulose. The film is then passed through several more baths, one to remove sulfur, one to bleach the film, and one to add glycerin to prevent the film from becoming brittle. Cellophane has a CAS number of 9005-81-6. The approximate chemical structures are shown in Fig. 13.3. The Cellophane may be coated with nitrocellulose or wax to make it impermeable to water vapor. It may also be coated with polyethylene or other materials to make it heat sealable for automated wrapping machines. Weathering Viscose is largely transparent to UV light, but prolonged exposure to sunlight weakens viscose rayon fibers. A 6-hour exposure of unstabilized viscose to UV light leads to a loss in in strength of about 4% [1]. Manufacturers Cellophane
and
trade
names:
Innovia
Figure 13.3 Conversion of raw cellulose to viscose.
427
Applications and uses: Cellulosic film applications include tapes and labels, photographic film, coatings for paper, glass, and plastic, fibers for clothing Data for cellophane/viscose polymers are found in Fig. 13.4.
13.1.2 Nitrocellulose Nitrocellulose is made by treating cellulose with a mixture of sulfuric and nitric acids. This changes the hydroxyl groups (2OH) on the cellulose to nitro groups (2NO3) as shown in Fig. 13.5. Nitrocellulose, also known as gun cotton and is the main ingredient of smokeless gunpowder, decomposes explosively. In the early 20th century, it was found to make an excellent film and paint. Nitrocellulose lacquer was used as a finish on guitars and saxophones for most of the 20th century and is still used on some current applications. Manufactured by (among others) DuPont, the paint was also used on automobiles sharing the same color codes as many guitars including Fender and Gibson brands. Nitrocellulose lacquer is also used as an aircraft dope, painted onto fabric-covered aircraft to tauten and provide protection to the material. Its CAS number is 9004-70-0. Nitrocellulose is not molded. It has been used in coatings and was widely used as automotive paint in the 1930s. The early types of nitrocellulose automotive lacquers showed signs of deterioration after a few months’ exposure in Florida. 2-(20 Hydroxy-30 ,50 -di-tert-butylphenyl)-5-chlorobenzotriazole (e.g., Tinuvin 327) is highly effective in stabilizing nitrocellulose coatings at a use level range of 0.5%2.0% and can be used in combination with phenolic and phosphate antioxidants, as
428
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ELASTOMERS
Figure 13.4 Effect of irradiation with UV light on the tensile strength retention of unstabilized viscose rayon to that stabilized with the sulfuric acid ester of 4-fl-hydroxyethylsulfonyl-2-aminoanisole [2]. UV, Ultraviolet. Table 13.1 Yellowness Index of Nitrocellulose in a Wood Coating Before and After 24 h Exposure to QUV-B 313 (UVB-313 Lamps Produce not only the Shortest Ultraviolet Rays that the Sun Emits, they Also Emit Unnaturally, Short-wavelengths Below What is Found on the Earth’s Surface) [3] Hours exposed
0
24
Yellowness index of nitrocellulose without UV stabilizer
1.0
18.3
Yellowness index of nitrocellulose with UV stabilizer
0.7
15.9
UV, Ultraviolet.
Figure 13.5 Structure of nitrocellulose.
well as hindered amine light stabilizers (HALS), to optimize performance in outdoor applications. Nitrocellulose is not usually used by itself for film applications, but more commonly is part of multilayered films structures, especially those based on cellophane. Manufacturers and trade names: Innovia Films Cellophane Applications and uses: Food wrap, coatings (for guitars) Data for nitrocellulose is found in Table 13.1.
13.1.3 Cellulose Acetate Cellulose acetate is the acetate ester of cellulose. It is sometimes called acetylated cellulose or xylonite. Its CAS number is 9004-35-7 and the approximate chemical structure is shown in Fig. 13.6. Cellulose acetate weathers well and is nonyellowing on long-term exposure to the sun, making it useful as a coating for signs and decals. The transparency of CA coatings and their ability to transmit sunlight, particularly beneficial UV rays, have led to extensive use of these film formers for coating wire screening for greenhouse windows, poultry runs, and similar structures. The good physical strength of the coatings yields a tough, tear-resistant screen [4].
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429
Manufacturers and trade names: Celanese Cellulose Acetate; Eastman Chemical Company Tenite; Daicel Corporation; Solvay Ocalio; Rotuba Applications and uses: Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters, found in screwdriver handles, ink pen reservoirs, and X-ray films Data for cellulose acetate is in Table 13.2.
13.1.4 Cellulose Acetate Butyrate
Figure 13.6 Chemical structure of cellulose acetate.
Cellulose acetate butyrate (CAB) is a mixed ester of cellulose. CAB, commonly known as butyrate, is resistant to UV rays, has lower moisture absorption than cellulose acetate and has extremely high impact strength. Its CAS number is 9004-36-8 and the approximate chemical structure is shown in Fig. 13.7.
Table 13.2 Remaining Weight of Samples of Cellulose Acetate With Various Plasticizers After Being Subjected to QUV Test Machine With Water Spray Accelerated Weathering Testing [5] Sample
Accelerated Weathering Time (h) 0
125
175
325
425
% Remaining weight Pure cellulose acetate
100
100
98
98
100
With 20 wt% polyethylene glycol
100
92
89
81
80
With 20 wt% triacetin
100
100
100
95
94
With 20 wt% tripropionin
100
100
100
94
87
With 20 wt% triethyl citrate
100
98
95
96
94
Figure 13.7 Chemical structure of cellulose acetate butyrate.
430
Manufacturers and trade names: Chemical Company Tenite; Uvex; Spartech
THE EFFECT
Eastman Excelon,
Applications and uses: Printing visual aids, page protection and animation cells Data for CAB polymers are found in Figs. 13.813.10.
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UV LIGHT
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WEATHER
ON
PLASTICS
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13.1.5 Ethyl Cellulose Ethyl cellulose is similar in structure to cellulose and cellulose acetate, but some of the hydroxyl (2OH) functional groups are replaced on the cellulose by the ethoxy group (OCH2CH3). Ethyl cellulose has a CAS number of 9004-57-3 and its structure is shown in Fig. 13.11.
Figure 13.8 Tensile strength at break after Arizona Weathering for Eastman Tenite Butyrate [2]. Note: 3.2-mm (0.125-in.) thick specimens of an outdoor type of Tenite butyrate [14].
Figure 13.9 Elongation at break after Arizona Weathering for Eastman Tenite Butyrate [2]. Note: 3.2-mm (0.125-in.) thick specimens of an outdoor type of Tenite butyrate.
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Figure 13.10 Impact strength after weathering for Eastman Tenite Butyrate [2]. Note: 3.2-mm (0.125-in.) thick specimens of an outdoor type of Tenite butyrate; samples weathered in a vertical position facing due south. Testing as per ASTM D3029.
Dow Ethocel does not discolor on exposure to strong sunlight nor does it promote the discoloration of plasticizers or polymers [6].
13.2 Polycaprolactone
Figure 13.11 Structure of ethyl cellulose.
Several phenolic stabilizers may be used with ethyl cellulose. Manufacturers and trade names: Dow Ethocel, Ashland Aqualon Applications and uses: Pharmaceutical applications, cosmetics, nail polish, vitamin coatings, printing inks, specialty coatings, and food packaging
Polycaprolactone (PCL) is biodegradable polyester with a low melting point of around 60°C and a glass transition temperature of about 260°C. PCL is prepared by ring opening polymerization of ε-caprolactone using a catalyst such as stannous octanoate. The structure of caprolactone and PCL is shown in Fig. 13.12. PCL is degraded by hydrolysis of its ester linkages in physiological conditions (such as in the human body) and has therefore received a great deal of attention for use as an implantable biomaterial. In particular, it is especially interesting for the preparation of long term implantable devices. A variety of drugs have been encapsulated within PCL beads for controlled release and targeted drug delivery. PCL is often mixed with starch to obtain a good biodegradable material at a low price. Perstorp offers PCLs under the trade name CAPAt. Low molecular weight PCLs may be added to other plastics to improve their weather resistance.
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Figure 13.12 Conversion of caprolactone to polycaprolactone.
Figure 13.13 Conversion of lactic acid to polylactic acid by two routes.
Manufacturers and trade names: Perstorp CAPA (previously Solvay), Dow Chemical Tone (discontinued) Applications and uses: The mix of PCL and starch has been successfully used for making trash bags in Korea (Yukong Company)
13.3 Poly(lactic acid) PLA is derived from renewable resources, such as cornstarch or sugarcanes. PLA polymers are considered biodegradable and compostable. PLA is a thermoplastic, high-strength, high-modulus polymer that can be made from annually renewable sources to yield articles for use in either the
industrial packaging field or the biocompatible/ bioabsorbable medical device market. Bacterial fermentation is used to make lactic acid, which is then converted to the lactide dimer to remove the water molecule which would otherwise limit the ability to make high molecular weight polymer. The lactide dimer, after the water is removed, can be polymerized without the production of the water. This process is shown in Fig. 13.13 and can proceed by two possible routes, the direct route and the lactide route. The PLA CAS number is 9002-97-5. Manufacturers and trade names: FKur Bio-Flex, Cereplast Inc. Compostables, Mitsubishi Chemical Fozeas, NatureWorks LLC Ingeo, Alcan Packaging Ceramis-PLA
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Applications and uses: Biomedical applications, such as sutures, stents, dialysis media, and drug delivery devices. It is also being evaluated as a material for tissue engineering, loose-fill packaging, compost bags, food packaging, and disposable tableware. PLA can be in the form of fibers and nonwoven textiles; potential uses: upholstery, disposable garments, awnings, and feminine hygiene products Data for PLA is shown in Figs. 13.1413.20.
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13.4 Poly-3-hydroxybutyrate Polyhydroxyalkanoates (PHAs) are naturally produced and include poly-3-hydroxybutyrate (PHB or PH3B), polyhydroxyvalerate and polyhydroxyhexanoate; A PHA copolymer called PHBV (PHB-co3-hydroxyvalerate) is less stiff and tougher, and it may be used as packaging material. Chemical structures of some of these polymers are shown in Fig. 13.21.
Figure 13.14 Tensile strength of poly(lactic acid) and polylactide during a weather ability test (accelerated test using a Weather-Ometer) [7].
Figure 13.15 Tensile strength of poly(lactic acid) and polylactide during an outdoor exposure test [7].
Figure 13.16 Ball Burst strength vs UV exposure time of Ingeo PLA fabric [8]. Note: Test Method: ASTM D3787; ATTCC 16E light exposure. UV, Ultraviolet; PLA, Polylactic acid.
Figure 13.17 Molecular weight loss vs UV exposure time of Ingeo PLA fabric [8]. Note: ATTCC 16E Light exposure. UV, Ultraviolet; PLA, Polylactic acid.
Figure 13.18 Color change vs UV exposure time of Ingeo PLA fabric [8]. Note: ATTCC 16E light exposure; HunterLab D65/10° Illuminator/observer. UV, Ultraviolet.
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Figure 13.19 Number average molecular weight dependence on ageing time at 50°C with and without. UV exposure and humidity of flame retarded PLA [9]. Note: Humidity tests using Memmert Humidity Chamber Model HCP 108, UV using a Q-LAB QUV chamber with and without water spray. UV, Ultraviolet; PLA, Polylactic acid.
Figure 13.20 Melting Tm dependence on ageing time at 50°C with and without UV exposure and humidity of flame retarded PLA. [9]. Note: Humidity tests using HCP 108 device, UV using a Q-LAB QUV chamber with and without water spray. Tm, Temperature; UV, Ultraviolet; PLA, Polylactic acid.
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Figure 13.21 Structures of several polyhydroxyalkanoates.
Figure 13.22 Tensile strength vs accelerated weathering exposure time of PHBV [10]. Note: Xenon-arc Weather-Ometer (Q-Sun Xe-1-S). The films were exposed to a repeated 2 h cycle of radiation followed by 2 h of radiation plus water spray. PHBV, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).
Articles made of PHB thermoplasts retain their original shape at 121 or 132°C. Because of this, perishable goods can be canned into packages produced of Biomer resins and preserved by steam sterilization.
Chemical Fozeas, NatureWorks LLC Ingeo, Alcan Packaging Ceramis-PLA, Metabolix/ ADM Tirel, Tianan Enmat, Copersucar Biocycle, Biomer Biomer L, Procter & Gamble Nodax
Manufacturers and trade names: FKur BioFlex, Cereplast Inc. Compostables, Mitsubishi
Applications and uses: Biomedical applications, such as sutures, stents, dialysis media, and drug
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Figure 13.23 Young’s modulus vs accelerated weathering exposure time of PHBV [10]. Note: Xenon-arc Weather-Ometer (Q-Sun Xe-1-S). The films were exposed to a repeated 2 h cycle of radiation followed by 2 h of radiation plus water spray. PHBV, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).
Figure 13.24 Elongation at break vs accelerated weathering exposure time of PHBV [10]. Note: Xenon-arc Weather-Ometer (Q-Sun Xe-1-S). The films were exposed to a repeated 2 h cycle of radiation followed by 2 h of radiation plus water spray. PHBV, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).
delivery devices. It is also being evaluated as a material for tissue engineering, loose-fill packaging, compost bags, food packaging, and disposable tableware. PLA can be in the form of fibers and nonwoven textiles; potential uses: upholstery, disposable garments, awnings, and feminine hygiene products Data for PHB plastics are found in Figs. 13.2213.24.
References [1] C. Panchigar, Compiled From Various Sources. Available from: https://www.scribd.com/doc/ 48749674/Property-of-Viscose. [2] T.B. Boboev, K.M. Makhkamov, B.N. Narzullaev, et al., Polymer Mechanics 10 (1974) 791. Available from: https://doi.org/ 10.1007/BF00857967.
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[3] Eastman Chemical Company, Eastmant Cellulose Ester Technical Tip, Controlling Yellowing in Wood Coatings, Eastman Chemical Company, 2013. [4] Eastman Chemical Company, Eastmant Cellulose-Based Specialty Polymers, Eastman Chemical Company, 2009. [5] R. Quintana, O. Persenaire, Y. Lemmouchi, J. Sampson, S. Martin, L. Bonnaud, et al., Enhancement of cellulose acetate degradation under accelerated weathering by plasticization with eco-friendly plasticizers, Polym. Degrad. Stab. 98 (9) (2013) 15561562. Available from: https://doi.org/10.1016/j.polymdegradstab. 2013.06.032. [6] Dow Chemical Company, ETHOCEL Ethylcellulose Polymers Technical Handbook, Dow Chemical Company, 2005. [7] M. Ajioka, K. Enomoto, K. Suzuki, A. Yamaguchi, The basic properties of poly
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(lactic acid) produced by the direct condensation polymerization of lactic acid, J. Environ. Polym. Degrad. 3 (1995) 225234. [8] Ingeo, NatureWorks LLC, UV Resistance, Technical Bulletin 370904, Ingeo, NatureWorks LLC, 2006. [9] N. Lesaffre, S. Bellayer, H. Vezin, G. Fontaine, M. Jimenez, S. Bourbigot, Recent advances on the ageing of flame retarded PLA: effect of UV-light and/or relative humidity, Polym. Degrad. Stab. 139 (2017) 143164. Available from: https://doi.org/ 10.1016/j.polymdegradstab.2017.04.007. [10] L. Wei, A.G. McDonald, Accelerated weathering studies on the bioplastic, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), Polym. Degrad. Stab. 126 (2016) 93100. Available from: https://doi.org/10.1016/j.polymdegradstab. 2016.01.023.