BIOPLASTICS | BIODEGRADABLE POLYMERS
tion of a sugar by defined lactic bacteria (such as Streptococcus, Pediococcus or Lactobacillus) in the absence of oxygen to form pyruvic acid. This is subsequently reduced to lactic acid. Lactic acid produced by fermentation is optically-active with L(+) and D(-) steroisomers obtained using the appropriate lactobacillus. On an industrial scale, high molecular weight
Right: Coffee capsules produced by ATI using Total-Corbion’s high heat resistant Luminy PLA
PLA is produced by ring opening of the lactide, resulting in four different forms depending on the lactide type used. L-PLA and D-PLA are the two optically-active regular forms; the other two optically-inactive forms are L,D-PLA and the meso-PLA form. Depending on the ratio of monomers D(-) and L(+), PLA can range from totally amorphous to 80% crystalline. The properties of PLA can be adjusted during polymerisation but many grades are characterised by low impact resistance, low elongation at break, poor barrier, low crystal- lisation rate, and low heat deflection temperature (HDT). Performance can be enhanced by blending with other polymers or by increasing the crystalline content (although the latter approach impacts negatively on biodegradation). Polybutylene succinate (PBS) is a biodegrad-
able linear polyester with a repeat unit molecular weight of 172 and carbon content of around 55.8%. The polymer has a crystallinity of 35-45%, a glass transition temperature of -32°C, and melting point of 114-115°C. It can trace its roots back to 1863, with more detailed work carried out by Wallace Hume Carothers at DuPont in the 1930s. It was not until the 1990s that interest was aroused again due to its biodegradable nature. Direct esterification of succinic acid with
About the author
Carmine Di Fiore is co-founder of MA Plastic Engineering, which provides specialist consultancy services to the compounding and masterbatch industries. His career has included R&D, production and raw material procurement roles. Over the past 15 years he has been closely involved in the development and production of biodegradable and compostable compounds for a variety of applications.
44 COMPOUNDING WORLD | September 2021
1,4-butanediol is the most common means of producing PBS. It is a two-step synthesis process where an excess of the diol is first esterified with diacid to form PBS oligomers through the elimina- tion of water. The oligomers are then polymerised under vacuum to obtain a high molecular weight polymer.
Initially developed to overcome the low elonga-
tion at break of PBS, polybutylene succinate adipate (PBSA) is produced by adding adipic acid to succinic acid during polymerisa- tion. The resulting copolymer shows some advantages in film produc- tion even though it has a relatively low melting point of 84°C. In other respects, PBSA shows similar properties to linear low-density polyethylene. PBSA biodegrades faster than PBS, making it suitable for applications such as composting bags. Polybutylene
adipate-co-terephthalate
(PBAT) is one of the most successful of a number of aliphatic polyesters developed to improve perfor- mance and reduce production cost. The glass transition temperature of PBAT is about -30°C and the melting temperature between 110-125°C. It is available commercially from BASF under the
Ecoflex name. PBAT is a random copolymer produced from
from terephthalic acid, 1,4-butanediol and adipic acid. The carbon content of commercial grades is around 64%. The presence of terephthalic acid in the polymer strengthens the copolyester structure and allows higher molecular weights to be ob- tained. At levels up to 40% it has minimal impact on biodegradability with at least 90% of the polymer metabolised within three months under composting conditions. PBAT is a flexible polymer with mechanical
properties similar to low density polyethylene (LDPE), which makes it suitable for food packaging and agricultural films. However, its relatively low tensile modulus means it is typically used in blends with other biodegradable polymers, such as PLA, and with mineral fillers. n This article is based on a longer and more detailed technical paper that covers synthesis and properties of currently available biodegradable polymers (the full version can be downloaded free of charge HERE).
difiore@mapeconsulting.it
www.compoundingworld.com
I
M A
G E
:
T
O T
A
L
-
C
O
R
B
I
O
N
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100
