Propylene Glycol, Monopropylene Glycol, Methylethylene Glycol, E1520, MPG, PG, 57-55-6, 4254-14-2, 4254-15-3

PROPYLENE GLYCOL (MONO PROPYLENE GLYCOL, MPG)

Propylene Glycol / Propan-1,2-diol / Mono Propylene Glycol / Methyl Ethylene Glycol / MPG / PG / E1520
CAS Number: 57-55-6 (also referenced as 4254-14-2, 4254-15-3 for enantiomeric forms)
EC Number: 200-338-0
E Number: E1520

SECTION 1: PRODUCT IDENTIFICATION AND CHEMICAL IDENTITY

Propylene Glycol is a clear, colorless, viscous, hygroscopic liquid with a slightly sweet taste. It is a synthetic organic compound belonging to the diol (glycol) family. It is produced primarily by the hydration of propylene oxide. It is widely used as a humectant, solvent, carrier, and cryoprotectant in food, pharmaceutical, cosmetic, and industrial applications. It is recognized as safe (GRAS) by the FDA and is approved as a food additive (E1520) in the EU.

SECTION 2: SYNONYMS AND OTHER NAMES

SECTION 3: CHEMICAL STRUCTURE

3.1. Molecular Structure

Propylene Glycol is a three-carbon diol with hydroxyl groups (-OH) on the first and second carbon atoms. It contains a chiral center at the second carbon, existing as two enantiomers (R and S forms).

Structural Formula:

        H
         |
   HO - C - H
         |
   HO - C - H
         |
        CH₃

Simplified Representation:
CH₃-CH(OH)-CH₂OH

3.2. Molecular Formula

C₃H₈O₂

3.3. Molecular Weight

76.10 g/mol

3.4. Key Structural Features

SECTION 4: PHYSICAL AND CHEMICAL PROPERTIES

SECTION 5: SPECIFICATIONS (USP/EP, FOOD GRADE)

SECTION 6: SOLUBILITY PROFILE

SECTION 7: CHEMICAL PROPERTIES AND REACTIVITY

SECTION 8: REACTION EQUATIONS

8.1. Esterification with Acids

PG + R-COOH → PG Ester + H₂O

8.2. Reaction with Isocyanates (Polyurethane Formation)

PG + 2 R-NCO → Polyurethane + CO₂

8.3. Dehydration (High Temperature)

2 PG → Dipropylene Glycol + H₂O

8.4. Oxidation (High Temperature)

PG + [O] → Lactic Acid → Pyruvic Acid (in the body)

SECTION 9: PRODUCTION METHOD

Propylene Glycol is produced primarily by the hydration of propylene oxide.

Alternative Production Method (Bio-Based): Glycerol (a by-product of biodiesel production) is hydrogenolyzed to produce bio-based propylene glycol. This product is chemically identical and is increasingly preferred in cosmetic and cleaning applications due to its sustainability profile.

SECTION 10: APPLICATIONS AND INDUSTRIAL USES

10.1. Food and Beverage Industry

Example Recipe – Lemon Flavor Emulsion Concentrate:

• 10% Propylene Glycol (solvent/carrier)

• 15% Lemon Essential Oil

• 10% Gum Arabic (emulsifier)

• 65% Water

Mix the flavor oil with propylene glycol. Add to gum arabic dissolved in water at high shear. Homogenize until stable emulsion is formed.

10.2. Pharmaceutical and Veterinary Industry

Example Recipe – Antiseptic Hydrogel:

• 20% Propylene Glycol (humectant/solvent)

• 1% Hydroxyethyl Cellulose (gelling agent)

• 0.05% Chlorhexidine Digluconate

• Q.S. Water

Disperse hydroxyethyl cellulose in water. Dissolve chlorhexidine in PG and incorporate into the gel with mixing.

10.3. Cosmetics and Personal Care

Example Recipe – Light Moisturizing Lotion:

• 4% Propylene Glycol

• 2% Glycerin

• 5% Caprylic/Capric Triglyceride

• 2% Cetyl Alcohol

• 0.5% Carbomer

• Q.S. Water

Neutralize carbomer to pH ~6 with triethanolamine. Add PG and glycerin to the water phase for enhanced skin moisturization.

10.4. Industrial Antifreeze and Heat Transfer Fluids

Freeze Protection Table:

Example Recipe – Food-Grade Cooling Fluid Concentrate:

• 90% Propylene Glycol

• 3% Water

• 7% Food-Compatible Corrosion Inhibitor Package (phosphates, azoles)

Dilute with deionized water to 35-40% solution on-site for use in brewery fermenter jacket cooling.

10.5. Polymer and Resin Production

Example Recipe – General Purpose UPR:

• 1.0 mol Phthalic Anhydride

• 1.0 mol Maleic Anhydride

• 2.2 mol Propylene Glycol

Esterify at 180-220°C until acid value reaches 20-30 mg KOH/g. Cool and dissolve in styrene (30-35% w/w) to obtain the final liquid resin.

10.6. Fog and Smoke Fluids

Example Recipe – Standard Fog Fluid:

• 25% Propylene Glycol

• 75% Deionized Water

Mix until homogeneous, filter before use. For denser and longer-lasting fog, increase PG ratio.

10.7. Other Applications

SECTION 11: ALTERNATIVES AND COMPARISON

11.1. Glycerol / Glycerin (E422)

11.2. Ethylene Glycol (MEG)

11.3. Dipropylene Glycol (DPG)

11.4. 1,3-Propanediol (Bio-PDO)

11.5. Butylene Glycol (1,3-Butylene Glycol)

SECTION 12: TOXICOLOGY AND SAFETY

12.1. Acute Toxicity

12.2. Regulatory Status

12.3. GRAS Status

Propylene Glycol is recognized as Generally Recognized as Safe (GRAS) by the FDA for use in food, pharmaceuticals, and cosmetics. The EFSA has established an ADI of 25 mg/kg body weight/day.

SECTION 13: GHS CLASSIFICATION

Signal Word: None (not classified as hazardous)

Hazard Pictograms: None

Hazard Statements (H-Codes): None

Safety Phrases (Historically):

SECTION 14: PRECAUTIONARY STATEMENTS (P-CODES)

SECTION 15: FIRST AID MEASURES

SECTION 16: FIRE-FIGHTING MEASURES

SECTION 17: ACCIDENTAL RELEASE MEASURES

SECTION 18: STORAGE AND SHELF LIFE

SECTION 19: PACKAGING OPTIONS

SECTION 20: TRANSPORT INFORMATION

SECTION 21: ENVIRONMENTAL INFORMATION

SECTION 22: REGULATORY INFORMATION

SECTION 23: FREQUENTLY ASKED QUESTIONS (FAQ)

Q1: Is propylene glycol safe for human consumption?
A: Yes. It is classified as GRAS (Generally Recognized as Safe) by the FDA. The EFSA has established an Acceptable Daily Intake (ADI) of 25 mg/kg body weight/day. It is metabolized through normal metabolic pathways to lactic acid and pyruvic acid.

Q2: What is the main difference between propylene glycol and ethylene glycol?
A: Toxicity. Ethylene glycol is highly toxic when ingested and can cause severe kidney damage. Propylene glycol is much less toxic and is recommended for applications where accidental ingestion or environmental release is possible (food processing coolants, RV antifreeze, animal-friendly de-icers).

Q3: Is propylene glycol suitable for vegan, halal, or kosher products?
A: Yes. Standard propylene glycol is synthetic (from propylene oxide hydration) and contains no animal-derived ingredients. Bio-based PG (from glycerol) is plant-derived. Certifications are available from manufacturers upon request.

Q4: What is the shelf life of propylene glycol?
A: At least 24 months from the date of manufacture when stored in tightly closed original packaging, in a cool, dry place, away from direct sunlight. After opening, keep tightly closed to prevent moisture absorption.

Q5: How should propylene glycol be transported and stored?
A: Store at ambient temperature (<40°C) in stainless steel, aluminum, or suitable plastic (HDPE, PP) containers. Carbon steel is not recommended for long-term storage due to slight acidity. Keep away from open flames (flammable liquid, flash point ~100°C). In case of spillage, absorb with inert material (sand, vermiculite) and dispose of according to local regulations. Prevent entry into sewers and watercourses.

Q6: Is propylene glycol flammable?
A: It is classified as a combustible liquid, not highly flammable. The flash point is approximately 100°C, so it does not readily ignite at room temperature. However, vapors can ignite if heated above the flash point in the presence of an ignition source. Ground tanks and containers during transfer.

Q7: Why is propylene glycol used in e-cigarette (vaping) liquids?
A: It serves as a carrier for flavor and nicotine, produces visible vapor, and provides a "throat hit" sensation. While PG is considered safe as a theatrical fog additive, the long-term effects of deep lung inhalation in e-cigarettes are still being researched.

Q8: Can propylene glycol cause skin irritation or allergic reactions?
A: True allergy (contact dermatitis) is rare but has been reported. It is generally considered a mild irritant at very high concentrations, so cosmetic formulators typically use it in the 1-10% range. Patch testing may detect sensitivity in a very small percentage of individuals.

Q9: What is the difference between mono propylene glycol (MPG) and dipropylene glycol (DPG)?
A: MPG is a single, defined molecule (propan-1,2-diol) with a molecular weight of 76.10 g/mol. DPG is a mixture of isomers (mostly 1,1'-oxybis-2-propanol, etc.) with a higher molecular weight (~134.17 g/mol). This gives DPG a higher boiling point, lower volatility, and different solvency properties. They are not directly interchangeable.

Q10: How is propylene glycol produced?
A: The main industrial method is the high-temperature hydrolysis of propylene oxide (200-220°C without catalyst, or 150-180°C with an ion-exchange resin catalyst). The bio-based route involves hydrogenolysis of glycerol (a biodiesel by-product). Bio-based PG is chemically identical and is increasingly preferred in cosmetics and cleaning products due to its sustainability profile.

SECTION 24: QUICK REFERENCE TABLE

SECTION 25: CRITICAL NOTICES AND BEST PRACTICES

CRITICAL NOTICES:

1. Toxicity Distinction: Propylene glycol is much less toxic than ethylene glycol. It is approved for food, pharmaceutical, and cosmetic use. Never confuse PG with ethylene glycol (MEG).

2. Hygroscopic Nature: PG is highly hygroscopic and absorbs moisture from the air. Store in sealed containers to maintain purity and prevent dilution.

3. Food Grade vs. Industrial Grade: Only USP/EP or food-grade PG should be used in food, pharmaceutical, and cosmetic applications. Industrial grades may contain impurities and are not suitable for human contact.

4. Flammability: PG is combustible (flash point ~100°C). It is not highly flammable at room temperature but vapors can ignite above the flash point. Ground tanks and containers during transfer.

5. Incompatibility: PG is incompatible with strong oxidizers, strong acids, and strong bases. Reaction with these materials may cause fire, explosion, or toxic gas release.

6. Bio-Based Alternatives: Bio-based PG (from glycerol) is chemically identical to petrochemical PG and is increasingly preferred for sustainability claims.

7. Vaping Use: While PG is considered safe as a theatrical fog additive, the long-term effects of deep lung inhalation in e-cigarettes are still being researched.

8. Allergic Reactions: True allergy (contact dermatitis) is rare but has been reported. Cosmetic formulators typically use it in the 1-10% range to minimize irritation risk.

BEST PRACTICE RECOMMENDATIONS:

• Storage: Store in a cool, dry, well-ventilated area. Maintain ambient temperature (15-40°C). Use stainless steel, aluminum, or HDPE/PP containers. Avoid carbon steel for long-term storage.

• Handling: Use chemical-resistant gloves, protective goggles, and appropriate clothing. Avoid prolonged skin contact.

• Transfer: Use sealed transfer systems. Ground all equipment during transfer. Avoid compressed air for transfer.

• Labeling: Clearly label all containers. Distinguish from ethylene glycol and other glycols.

• Quality Control: For food/pharmaceutical applications, ensure product meets USP/EP or food-grade specifications. Test for purity, water content, and heavy metals.

• Waste Management: Dispose of PG and contaminated materials in accordance with local regulations. Do not pour down drains.

LEGAL DISCLAIMER:

This Technical Data Sheet (TDS) is for informational purposes only and is prepared based on available technical data. The user is solely responsible for determining the suitability of the product for their specific application and for complying with all local, national, and international regulations. For complete safety, storage, handling, transport, waste, and regulatory compliance information, the official Safety Data Sheet (SDS/MSDS) provided by the manufacturer/supplier must be consulted. Propylene glycol is a combustible liquid and should be handled with appropriate precautions. This document does not substitute professional or medical advice.