Chemistry for Engineers: Biodegradable Plastics

Prayer Before Class

• Holy Spirit is the true source of light and wisdom
• Prayer requests a penetrating mind for understanding
• Prayer requests a retentive memory for easy learning
• Prayer requests clarity and ease of expression
• Prayer requests guidance and success in the work
• Prayer is made through Jesus Christ, the Father, and seeks eternal reign

Post-Laboratory Discussion: Preparation of Biodegradable Plastics

• The discussion is about biodegradable plastics, specifically, the preparation of them.
• It's part of a Chemistry for Engineers Laboratory.

Learning Objective

• Students are expected to create a plastic film from potato starch.

PLASTICS

• Plastics are derived from petroleum oil.
• Plastics rely heavily on scarce fossil fuels.
• Burning plastics releases carbon dioxide which contributes to global warming.
• Plastics take a long time to decompose.

Decomposition Times of Materials

• Batteries: 110 years
• Vegetables (leaves, branches): 1-6 months
• Food waste: 1 month
• Newspapers: > 1 month
• Office papers: ~2 years
• Wax paper: up to 5 years
• Stub filter: 2-3 years
• Chewing gum: 30 years
• Natural fabrics clothes: 2-3 years
• Synthetic clothes: up to 40 years
• Shoes (natural): 10 years, (synthetic): 80 years
• Iron cans: 10 years
• Tin cans: 90 years
• Aluminum cans : 500 years
• Polyethylene bags and plastic bottles: 100-200 years
• Baby diapers: 200-500 years
• Rubber tires: 120-140 years
• Glass: 1000 years

What are BIOPLASTICS?

• Bioplastics are plastics derived from renewable biomass sources, such as vegetable oil or corn starch.

Types of Bioplastics

• Starch-based: made from natural starch; used for packaging and drug capsules.
• Cellulose-based: made of cellulose esters; used in thermoplastics and packaging.
• Protein-based: made from proteins (soy, wheat); used for body panels in automobiles.
• Some aliphatic polyesters

Characteristics of Petroleum-based and Bioplastics

• Energy consumption: Bioplastics use 48% less energy than petroleum-based plastics.
• Raw Materials: Petroleum-based plastics use petroleum, a non-renewable resource. Bioplastics use renewable biomass sources (starch, corn, sugarcane, potato).
• Carbon Footprint: Petroleum-based plastics have a high carbon footprint. Bioplastics have a 62% lower carbon footprint than traditional plastics.
• Presence of chemicals: Petroleum-based plastics may contain Bisphenol A (BPA). Bioplastics do not contain any toxic chemicals.
• Physical properties: Both types are stable, although Bioplastics have high thermo-plasticity.
• Biodegradability: Bioplastics can decompose in natural settings in ~180 days. Petroleum-based plastics take > 1000 years to decompose completely.

Biodegradability

• Biodegradation is the breakdown of organic materials by natural processes and microorganisms.
• Factors that contribute: sunlight, water, bacteria, enzymes, wind abrasion.

Biodegradation of Bioplastics

• Biodegradation can be facilitated by bacteria in soil, such as Pseudomonas and Streptococcus species.
• Addition of glycerol to potato starch based bioplastics increases the degradation of the bioplastic as it helps the material absorb water.
• Water is a medium for most bacteria and microbes.

Degradable Plastics Types

• Biodegradable: contain a small percentage of non-oil-based materials like corn starch.
• Photodegradable: break down when exposed to sunlight.

Potato Starch

• Potato starch is a polymer made of glucose units.
• It contains two carbohydrate polymers: amylose (long-chain) and amylopectin (highly-branched), with amylopectin making up the majority.

Potato Starch Based Bioplastic

• HCl breaks down amylopectin to enable film formation.
• Glycerol acts as a plasticizer, increasing the flexibility and elasticity of the bioplastic.
  • Glycerol disrupts hydrogen bonds in the starch, weakening the structure and enabling further plasticity.
  • Glycerol increases the bioplastic's ability to absorb moisture further increasing its flexibility.

End of discussion