Bio-PE, Bio-PET & Drop-In Bio-Based Polymers: Fermentation, Synthesis & De-fossilisation

Drop-in bioplastics like Bio-PE and Bio-PET offer an immediate route to de-fossilise packaging because they have the exact same chemical structure, properties, and processing settings as their fossil-based counterparts. This allows brands (e.g., Coca-Cola, L'Oréal, Unilever) to swap materials without modifying their injection moulding or blow moulding tools. In India, companies like India Glycols and Godrej Industries produce bio-monoethylene glycol (bio-MEG) and derivative bio-based polymers to satisfy brand sustainability pledges.

• Define "drop-in" bioplastics and compare them with novel bio-based polymers like PLA and PHA.
• Trace the chemical synthesis route from sugarcane molasses to Bio-ethylene and Bio-polyethylene (Bio-PE).
• Detail the synthesis of Bio-PET from bio-MEG and fossil-derived or bio-purified terephthalic acid (PTA).
• Calculate the bio-based carbon content of a polymer blend using radiocarbon analysis parameters (ASTM D6866).
• Identify ASTM D6866 and ISO 16620 standards for bio-based content verification.

3.1 Drop-In Bioplastics Definition

Drop-in bioplastics are chemically identical to fossil-based polymers but derived from renewable biomass resources (sugarcane, corn, cellulosic waste). Examples include Bio-PE, Bio-PP, Bio-PET, and Bio-PVC.

• Advantage: They can be processed using existing machinery and are 100% recyclable in existing recycling streams (e.g., Bio-PE recycled alongside fossil-PE).
• Limitation: They are non-biodegradable and persist in the environment just like conventional plastics.

3.2 Synthesis of Bio-Polyethylene (Bio-PE)

1. Fermentation: Yeast ferments sugars from sugarcane juice/molasses to produce bio-ethanol:

1. Dehydration: Ethanol is vaporised at 300–400°C over a solid acid catalyst (e.g., alumina or zeolite) to yield bio-ethylene gas:

1. Polymerization: High-purity bio-ethylene is polymerized using Ziegler-Natta or metallocene catalysts to produce HDPE, LLDPE, or LDPE.

3.3 Synthesis of Bio-Polyethylene Terephthalate (Bio-PET)

PET is made by esterifying Terephthalic Acid (PTA) with Monoethylene Glycol (MEG):

• Bio-MEG: Produced by dehydrating bio-ethanol to ethylene, oxidising to ethylene oxide, hydrolysing to glycol. Represents 30% of PET's mass.
• Bio-PTA: Can be produced from bio-isobutanol via p-xylene oxidation, but is commercially rare. Most Bio-PET on the market today is 30% bio-based (fossil PTA + bio-MEG).

3.4 Bio-based Carbon Content (ASTM D6866)

Bio-based content is measured using radiocarbon ($^{14}\text{C}$) dating. Fossil carbon contains zero $^{14}\text{C}$ due to radioactive decay (half-life $\approx 5730$ years), whereas modern biomass contains a constant atmospheric equilibrium ratio of $^{14}\text{C}/^{12}\text{C}$:

Problem: A packaging film is produced by blending 40 wt% Bio-PE ($100\%$ bio-based carbon) with 60 wt% conventional fossil-derived PET ($0\%$ bio-based carbon). What is the total bio-based carbon content of this blend as determined by ASTM D6866?

Solution:

1. Identify carbon fraction of each constituent polymer:

• Polyethylene (PE) monomer: $+(\text{CH}_2-\text{CH}_2)+ \Rightarrow$ carbon fraction $\omega_{\text{C,PE}} = \frac{24}{28} = 0.857$ (85.7% carbon by weight)
• Polyethylene Terephthalate (PET) monomer: $+(\text{C}_{10}\text{H}_8\text{O}_4)+ \Rightarrow$ carbon fraction $\omega_{\text{C,PET}} = \frac{120}{192} = 0.625$ (62.5% carbon by weight)

1. Calculate carbon mass per kg of blend:

• Mass of carbon from Bio-PE: $0.40 \text{ kg} \times 0.857 = 0.3428$ kg of bio-carbon
• Mass of carbon from fossil-PET: $0.60 \text{ kg} \times 0.625 = 0.3750$ kg of fossil-carbon
• Total carbon mass in 1 kg blend: $0.3428 + 0.3750 = 0.7178$ kg

1. Calculate the percentage of bio-based carbon:

Interpretation: Although the blend contains 40% Bio-PE by weight, the bio-based carbon fraction as measured by ASTM D6866 is 47.76% because PE has a higher carbon density than oxygen-containing PET.

India Glycols Limited (IGL) (Kashipur, Uttarakhand) is a pioneer in green chemistry, operating a large-scale plant that synthesizes bio-MEG from sugarcane ethanol. They export bio-MEG to global packaging leaders for the production of bio-based PET bottles.

Under India's voluntary green labelling standards, manufacturers submit compounds to laboratories equipped with liquid scintillation counters to certify bio-based content under ASTM D6866.

• Drop-In Plastic: Chemically identical to fossil plastics but biomass-derived; fully compatible with existing processing and recycling.
• Bio-MEG: Bio-based monoethylene glycol; forms the 30% bio-based portion of standard Bio-PET.
• ASTM D6866: The definitive standard method for testing bio-based carbon content using radiocarbon analysis.
• Dehydration: Chemical reaction removing water; converts bio-ethanol to bio-ethylene.

1. ASTM D6866 — Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis
2. ISO 16620-1 — Plastics — Biobased content — Part 1: General principles
3. ISO 16620-2 — Determination of biobased carbon content
4. EN 16640 — Bio-based products — Bio-based carbon content — Determination using radiocarbon method

1. Contrast the environmental profiles of Bio-PET (non-biodegradable, recyclable) and PLA (biodegradable/compostable, non-recyclable in PET stream).
2. Why is raw sugarcane molasses preferred over corn starch as the feedstock for bio-ethanol fermentation in the Indian tropical context?
3. If a polymer sample contains a mixture of $70\%$ bio-based carbon and $30\%$ fossil carbon, predict the $^{14}\text{C}$ activity of the sample relative to a modern wood reference standard.

Q1. What is the primary chemical transformation required to convert bio-ethanol into bio-ethylene?

• A) Catalytic dehydration

Q2. Which of the following is true for Bio-PE?

• C) It is chemically identical to fossil-PE and is fully recyclable in the PE stream

Q3. Commercial Bio-PET is typically 30% bio-based because:

• B) It is synthesised from bio-MEG (30% weight) and fossil-PTA (70% weight)

Q4. What method is specified by ASTM D6866 to verify bio-based carbon content?

• C) Radiocarbon ($^{14}\text{C}$) analysis

Q5. Which Indian company is a major producer of bio-MEG from sugarcane?

• B) India Glycols Limited