Biopolymers: Properties, Processing, and Applications

Biopolymers are naturally occurring polymers, which are produced by living organisms. They are distinct from synthetic biodegradable polymers.

There has been growing concern about the negative impacts of environmental pollution from fossil fuels and waste from petrochemical products. A lot of research has gone into exploring other alternatives to petroleum-based products which would be renewable as well as bio-degradable and thus pose a lesser risk to the environment. Biopolymers are one such possible solution to the problem because they are typically biodegradable materials obtained from renewable raw materials. However, it must be noted that not all biodegradable polymers are biopolymers (i.e. produced from renewable resources). As one might expect, there are challenges related to biopolymers such as their limited rate of production, cost of production and the suitability of their properties.

Some of the first modern biomaterials made from natural biopolymers include rubber, linoleum, celluloid and cellophane. The latter two are made using cellulose, which is the most naturally abundant biopolymer and the most abundant organic material on Earth, making up a third of all plant matter. Since the middle of the 20th century, these human-made biopolymers were virtually all replaced with petrochemical-based materials. However, due to growing ecological concerns, biopolymers are enjoying renewed interest from the scientific community, the industrial sector and even in politics [1].

In this article, you will learn about: 

  • The properties of biopolymers
  • The production and processing of biopolymers
  • Applications of biopolymers
  • Examples of biopolymers
  • The future of biopolymers

Properties of biopolymers

The main interest in biopolymers is to replace many of the everyday items which are made from petroleum products. This means that they will be required to exhibit similar, if not better, properties than the materials they replace to make them suitable for the various applications that they will be put to. Much of the property measurements of biopolymers have variance due to factors such as degree of polymerisation, type and concentration of additives, and presence of reinforcement materials. Information about the properties of biopolymers is not as extensive as for traditional polymers, but there is still a considerable depth of investigation into their physical, mechanical, thermal properties [2].

Some biopolymers have been identified to possess electronic and ionic conductivity and have thus been termed electro-active biopolymers (EABP). This has given them the potential to replace other synthetic materials. These biopolymers, which include starch, cellulose, chitosan and pectin, show a wide-ranging electrical conductivity between 10-3 and 10-14 S/cm [3].

Table 1. Physical, mechanical and thermal properties of some commercial biopolymers.

(You can also compare these materials visually on the Matmatch comparison page)

Biopolymer

Density

at 20 °C

Tensile strength

at 20 °C

Flexural modulus 

at 20 °C

Melting point

Elongation

at 20 °C

PLA Luminy® LX530

1.24 g/cm³

50 MPa

N/A

165 °C

5 %

TYÜP BMF 990

1.26 - 1.3 g/cm³

40 MPa

N/A

110 - 120 °C

300 %

NuPlastiQ®BC 27240

1.3 g/cm³

12MPa

0.24 GPa

140 - 160 °C

272 %

Extrudr Wood Filament

1.23 g/cm³

40 MPa

3.2 GPa

150 - 170 °C

N/A

EVO 719

1.3 g/cm³

40 MPa

2 GPa

140 °C

30 %

Injicera CHX 0113

1.11 g/cm³

14 MPa

0.48 GPa

165 °C

59%

CR1 1013

1.1 g/cm³

9 MPa

4.43 GPa

132 °C

89 %

The production and processing of biopolymers

There are many different methods and techniques used to produce biopolymers. Since most of these polymers already exist in nature or are produced by natural organisms, these processes are often a matter of extraction followed by synthesis. They may include a combination of any of fermentation, filtration, compounding/granulation, hydrolysis, esterification, poly-condensation, oxidation and dehydration. Below is an example of the production process involved in making polybutylene succinate (PBS).

Figure 1. Process route for the production of polybutylene succinate (PBS) with bio-based succinic acid (PBS bb SCA) [1].

Applications of biopolymers

Biopolymers are used in many industrial applications as well as food packaging, cosmetics and medicine [4]. They can replace traditional petroleum-based plastics in many applications. Some biopolymers have also been applied to specific uses that other plastics would not be suitable for, such as in the creation of artificial tissue. These applications may require biocompatible and biodegradable materials with sensitivity to changes in pH as well as physicochemical and thermal fluctuations [5].

Biopolymers, in general, often exhibit poor mechanical properties, chemical resistance and processability in comparison to synthetic polymers. To make them more suitable for specific applications, they can be reinforced with fillers which drastically improve these properties. Biopolymers that have been reinforced in this way are called biopolymer composites. The table below is a summary of some common biopolymer composites, their properties and the industries in which they are already widely used.

Table 2. Summary of biopolymer composites production methods, properties, and applications [6].

Matrix/Filler

Production Method

Properties

Applications

PLA/PEG/Chit

Extrusion

Low stiffness/

High flexibility

Bone & dental implants food packaging

PLA/Cellulose

Extrusion/injection

Improved rigidity & biodegradability

Packaging, automotive

PLA/Potato pulp

Extrusion/injection

Low stiffness & ductility, good processability

Food packaging

PLA/MgO

Solution casting

Improved stability and bioactivity

Medical implants, tissue engineering, orthopaedic devices

PHB/wood sawdust fibres

Extrusion

Improved degradation in soil

Agriculture or plant nursery

PHBV/TPU/cellulose

Extrusion/injection

Balanced heat resistance, stiffness, and toughness

Food packaging tissue engineering

Nanocellulose/CNT

Cast moulding

Good electrical conductivity

Super-capacitor, sensors

Rubber/potato starch

Roller mixing

Accelerated thermal ageing

Vibration isolators, shock mounts, electrical components

Potato starch/wheat gluten

Compression moulding

Improved maximum stress & extensibility

Development of bio-based plastics

Alginate/cinnamon oil

Solution casting

Good antibacterial activity

Active packaging materials

PVA/Chitosan

Electro-spinning

Good chemical stability

Drug delivery food packaging

PPC/TPU

Melt compounding

Good thermal stability & stiffness

Electronic packaging applications

Examples of biopolymers

Biopolymers can be classified broadly into three categories based on their monomeric units and structure:

  • Polynucleotides: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
  • Polysaccharides: cellulose, chitosan, chitin, etc.
  • Polypeptides: collagen, gelatin, gluten, whey, etc.


Biopolymers can also be categorised by other criteria such as their base materials (animal, plant or microbial), their biodegradability, their synthesis route, their applications or their properties.

Examples of some commercially-produced biopolymers include [1]:

  • Bio-based polyesters such as polylactic acid (PLA), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polytrimethylene terephthalate (PTT)
  • Bio-based polyolefins such as polyethylene (Bio-PE)
  • Bio-based polyamides (Bio-PA) such as homopolyamides (Bio-PA 6, Bio-PA 11) and copolyamides (Bio-PA 4.10 – Bio-PA 5.10 – Bio-PA 6.10, Bio-PA 10.10)
  • Polyurethanes such as Bio-PUR
  • Polysaccharide polymers such as cellulose-based polymers (regenerated cellulose, cellulose diacetate) and starch-based polymers (thermoplastic starch, starch blends)

The future of biopolymers

The figure below shows the increase in bio-based polymer production between 2017 and what is estimated to be the case in 2022. Furthermore, it is projected that biodegradable biopolymers will constitute a larger percentage of biopolymer production in the coming years. It is clear to see that biopolymer production is on an upward trajectory. While it has a long way to go, if it is to take over from petroleum products, production is forecasted to increase from 2.27 million tonnes in 2017 to 4.31 million tonnes in 2022. This is at least partly a result of public demand and government regulations, which will continue to have a significant impact.

Figure 2. New Economy bioplastics production capacities by material type [1].

Sources

[1] "Biopolymers, facts and statistics," Institute for Bioplastics and Biocomposites, Hochschule Hannover, ISSN (Print) 2363-8559, ISSN (Online) 25103431, Edition 5, 2018. [Online]. Available:https://www.ifbb-hannover.de/files/IfBB/downloads/faltblaetter_broschueren/Biopolymers-Facts-Statistics-2018.pdf. [Accessed Apr. 2, 2020].

[2] K. Van de Velde and P. Kiekens, "Biopolymers: overview of several properties and

consequences on their applications," Polym. Test. 21 (2002) 433–442, Aug. 2001.

[3] S. Muthulakshmi, “Investigations on the biopolymers papain, gum acacia, gum tragacanth and gum guar: Physical and antimicrobial properties,” PhD dissertation, Department of Physics, Manonmaniam Sundaranar University, Tirunelveli, 2013.

[4] M. E. Hassan, J. Bai and D. Dou, "Biopolymers; Definition, Classification and Applications," Egypt. J. Chem. Vol. 62, No. 9. pp. 17251737, 2019.

[5] L. Altomare, L. Bonetti, C. E. Campiglio, L. De Nardo, L. Draghi, F. Tana and S. Farè, "Biopolymer-based strategies in the design of smart medical devices and artificial organs," Int J Artif. Organs. Vol. 41, No. 6. pp. 337–359, 2018.

[6] A. M. Díez-Pascual, "Synthesis and Applications of Biopolymer Composites," Int. J. Mol. Vol. 20, 2321, 2019.