Green Plastics and Polyamides

• "Green plastics" refer to bioplastics made from renewable materials that mimic the look, feel, and performance of petrochemical-based plastics.
• Rising oil prices, global interest in renewable resources, and worries about greenhouse gases and plastic waste have increased interest in biopolymers and bioplastics.
• Monomer origin and chemistry of a product are both important factors when making green plastics.
• Proteins, carbohydrates, and fats/oils are naturally occurring polymers.

Protein

• Proteins include starch, hair, silicate chains in rocks, silk, cotton fibres, and cellulose in woody plants.
• Proteins range in molecular weight from 6,000 to 1,000,000 grams per mole.
• The building blocks of all proteins are α-amino acids, which link together through amide/peptide linkages via condensation reactions to form protein polymers in a stepwise process.

Hydrogen Bonding in Polyamides

• Polyamides, like nylon, exhibit hydrogen bonding between N-H groups and carbonyl groups in adjacent chains, enhancing their strength.

Proteins Structure

• Proteins consists of peptide, dipeptide, or polypeptide chains made from 20 amino acids.
• The sequence is assembled in any order.
• The construction of proteins has infinite variety.

Fats/Oils

• Fats/oils are naturally occurring polymers.

Carbohydrate

• Carbohydrates can be monosaccharides (glucose, fructose), disaccharides (sucrose), or polysaccharides (starch, cellulose, glycogen).
• Polysaccharides are large polymers made of many monosaccharide glucose units.
• Sugar can be sourced from crops (1st generation) or waste products (2nd generation), with the latter potentially suitable for fermentation to bioethanol.

Modified Natural Polymer (Protein)

• Adolf Spitteler, a Bavarian chemist, created a hard, waxy substance from a formaldehyde spill in his lab.
• Milk paint used by 18th-century farmers to create waterproof coatings via mixing buttermilk, lime (calcium oxide, CaO), and colorant.

Modified Natural Polymer (Fat/Oil)

• Henry Ford and Robert Boyer's Soybean Car, which uses modified fat/oil polymers.

Modified Natural Polymer (Carbohydrate)

• Cellulose acetate comes from modifying other natural sources.

Natures Biopolymers

• Polyhydroxyalkonates or PHAs are biocompatible and biodegradable, making them useful in biomedical applications like controlled drug delivery and surgical sutures.
• PHAs are linear polyesters produced naturally by bacteria through the fermentation of sugar or lipids, used by the bacteria to store carbon and energy.
• Maurice Lemoigne, a French microbiologist, first isolated and characterized PHAs in 1923.

Polyhydroxybutyrate (PHB)

• Polyhydroxybutyrate (PHB) is a linear thermoplastic polyester made through controlled bacterial fermentation.
• It was discovered by Maurice Lemoigne in 1923.
• Next-generation PHB derives from transgenic plants or micro-organisms.
• The cost is typically $1-2 per pound.

Bacterial Polyester

• Bacteria can be used to make a bacterial polyester PHA (A polyhydroxyalkanoate)
• Alternative feedstocks include glycerol (from biodiesel production), starch, and triglycerides.
• Advantages of Bacterial Polyesters
• Biodegradable and eco-friendly to synthesise.
• Excellent processability and is from a renewable resource with with good mechanical properties
• Shortcomings of Bacterial Polyesters
• Limited reactive groups which has a Narrow processing window, and is suseptible to thermal degradation which results in brittleness

Monomers from Nature

• Polymerizable monomers occur biologically.
• The polymers themselves are not produced naturally.
• Polymers have the properties of biopolymers, and are biodegradable.
• Typical monomers are Lactic acid, amino acids and triglycerols.

Polylactic Acid

• Polylactic acid (PLA) or polylactide, is a biodegradable, thermoplastic aliphatic polyester from renewable resources like corn starch (in the US) or sugarcane.
• Bacterial fermentation creates lactic acid and is oligomerized and catalytically dimerized to produce the monomer for ring-opening polymerization which produces a high molecular weight form with a stannous octoate catalyst.

PLA Uses

• PLA is for biomedical applications such as sutures, stents, dialysis media, and drug delivery devices and is also tested for tissue engineering.
• PLA is biodegradable, therefore it can be used in bioplastics, compost bags, food packaging, disposable tableware, fibers, and non-woven textiles.
• PLA can also be used in disposable garments, upholstery, feminine hygiene products, and nappies.
• PLA can replace PET in selected applications like cellophane and garbage bags
• Short shelf life bottles like still water, juice and dairy beverages are suitable for PLA
• PLA products are both biodegradable and compostable

Biodegradability

• Packaging made from PLA is biodegradable
• Degrades within 60 days under commercial composting installations

Biopolymers

• Biopolymers often have oxygen or nitrogen atoms in their polymer backbone.
• Synthetic polymers with only C-C single bonds in their backbones are resistant to biodegradation.

Polymers From Renewable Resources

• Monomers are obtained from renewable resources.
• One or more synthetic steps may be required to turn the monomers into a polymer (so not necessarily biodegradable).

Ethanol Renewable Polyethylene

• Bipoly ethylene, also known as renewable polyethylene uses bio ethanol and is produced from biomass, corn and sugar switchgrass.
• Ethanol becomes ethylene after dehydration.

Other Green Approaches

• 1,3 butadiene comes from ethanol.

Polyethylene Terephthalate

• PET was first synthesized in North America in the mid-1940s by DuPont chemists searching for new synthetic fibers.

PET New Directions

• Terephthalate polyesters such as PET have been prepared from renewable terephthalic acid and proven to be bio-based through radiocarbon analysis.

Polymers from Oils

• Triglyceride structure of the vegetable oils.
• Polymers from oils include free radical, cationic and condensation polymerization.
• polyesters are also obtained from oils by polycondensation and ring openers.

Nylon Synthesis

• The original nylon synthesis used less ideal reagents, high pressure and high temperature (280°C).
• Adipic acid, a precursor, was initially created by oxidative cleavage of cyclohexene with nitric acid which also generated a significant amount of non-natural nitrogen oxide (“NOx”) emissions
• More environmentally friendly than nitric acid.

Alternative Routes to Adipic Acid

• KMnO4 This synthesis is more environmentally friendly than the industrial nitric acid route, though it still involves a potent oxidizer and generates significant quantities of MnO2 waste.
• Greener Route
• Na2WO4, H2O2

KHSO4, Aliquat 336 has a yield of 65%

• Sodium tungstate (Na2WO4) can create a catalyst for the hydrogen peroxide oxidation of cyclohexene to adipic acid.
• This is a greener method and avoids the need for a strongly basic reaction medium, and generates only water as a byproduct.

Improvements to Nylon 6,6 Synthesis

• To achieve it at low pressures, Adipoyl chloride (or adipoyl dichloride) is a di-acyl chloride with formula C6H₈Cl₂O₂
• Nylon 6,6 can then be synthesized under normal atmospheric pressures by interfacial polymerization.
• Combine adipic acid and thionyl chloride to create the desired compound at 55-65 degrees.

Room Temperature Interfacial Condensation Polymerisation

• At room temperature components can be combined for condensation polymerisation.

Nylon Synthesis (Biocatalysis)

• Cancer mutations have inspired a redesign of an enzyme to catalyse a key step in the bio-based production of adipic acid.