Compared with synthetic polymers, natural polymers and biopolymers are polymer compounds formed by biochemistry or photosynthesis in nature or minerals. They are found in animals, plants, or minerals, such as cellulose, starch, protein, lignin, natural rubber, asbestos, mica, nucleic acids. Natural polymers and biopolymers often contain other macromolecular substances or mineral impurities, which can be purified, processed or modified by physical and chemical methods. They are widely used in industry, agriculture, transportation and people's lives.

Figure 1. Biodegradable polymers used in the medical field.

Applications:

Natural polymers and biopolymers can be used in biomaterials, antibacterial materials, coatings, shape-memory materials and other fields.

• Biomaterials: In terms of biomaterials, natural polymers and biopolymers can be used as cytocompatible materials. A tunable poly (phthalamide) (BDIS) is synthesized by melt co-polycondensation of four biological monomers, salicylic acid (SA), itaconic acid (IA), 1,10-decanediamine (DD) and 1,4-butanediamine (BD). The obtained poly (phthalamide) is a new type of poly (phthalamide) which combines many properties, such as low melting point of semi crystal poly (phthalamide), high toughness of amorphous poly (phthalamide), and high elastic of poly (phthalamide). In addition, the cytotoxicity test in vitro shows that the polyphthalamide is non-toxic to mouse fibroblasts and has great application potential in biomaterials.
• Antibacterial materials: In the field of antibacterial materials, natural polymers and biopolymers have a good application prospect as a new type of antibacterial polymer material. A new type of antibacterial poly, ethylene terephthalate (PET), can be prepared from biological monomers derived from vanillin. PET can be modified by a two-step method: the photoinitiator is first grafted with N-N-diethylenediamine by PET ammonolysis. Then, the photopolymerization of biological acrylamide monomers is carried out by grafting. The results of bioassay show that the modified material has potential antibacterial properties against Gram-positive cocci, Staphylococcus aureus, Escherichia coli and so on.

Figure 2. Polyethylene terephthalate.

• Coating: In the field of coatings, natural polymers and biopolymers have good comprehensive properties and show good application prospects. For example, a thin film coating can be formed by light-curing using a mixture of acrylic epoxy soybean oil (AESO) and betulin (which can be extracted in large quantities from birch trees). The elastic modulus, tensile strength, hardness and wear resistance of the cured film increase, while the fracture strain decrease. And the addition of AB comonomer can increase the glass transition temperature of cured AESO polymer. In addition, some researchers use cardanol-derived methacrylic acid monomer (CAMA) to perform emulsion polymerization in toluene or aqueous medium with sodium lauryl sulfate as a surfactant to obtain cardanol aromatic biobased polymer latex. The results show that the particle size of the stabilized latex obtained is between 25-75 nm, and it has a single glass transition temperature, which is suitable for coating applications.

Figure 3. Diagram showing the preparation of latex paint using cardanol-derived methacrylic acid monomer.

• Shape memory material: As a kind of promising shape-memory materials, natural polymers and biopolymers have good shape memory properties and can be used as continuous conversion switches. For example, the biobased poly (propylene sebacate) synthesized from 1,3-propylene glycol, sebacic acid and itaconic acid is a kind of shape memory material with good shape recovery and immobilization properties.

References:

1. Zeng C, Seino H.(2013) "Self-healing bio-based furan polymers cross-linked with various bis-maleimides." Polymer, 54(20):5351-5357.
2. Dumas L, Bonnaud L.(2016) "High-performance bio-based benzoxazine networks from resorcinol and hydroquinone." European Polymer Journal, 75(2):486-494.