At a Glance

Propylene glycol (PG) and dipropylene glycol (DPG) are two multi-purpose ingredients employed in personal care and industrial use, respectively, but both of them differ significantly in composition, characteristics, and application. PG is light in weight, strongly hygroscopic, approved by the FDA for food and drugs, and perfect for products that need quick absorption and hydration. Conversely, DPG is heavier in molecular weight, less volatile, and superior as a carrier in fragrances, air fresheners, and industrial solvents. The choice between them is based on application requirements, regulatory needs, performance requirements, and cost factors. Elchemy provides high-quality PG and DPG to suit various business requirements.

Introduction

The compounds dipropylene glycol and propylene glycol are found in many products, from cosmetics and skin care to industrial solvents and antifreeze. Yet they are likely to be confused with each other, and the question arises, “Is dipropylene glycol the same as propylene glycol?“

It is crucial for manufacturers, suppliers, and formulators in the personal care and industrial markets to understand the difference between dipropylene glycol vs propylene glycol. This blog demystifies their chemical structures, properties, applications, and regulatory requirements to enable you to make an informed choice.

What Are Propylene Glycol and Dipropylene Glycol?

First, let’s define both chemicals before comparing propylene glycol with dipropylene glycol.

Propylene Glycol

Propylene glycol is a synthetic liquid alcohol that usually absorbs moisture and serves mainly as a solvent. It has FDA approval for inclusion in food, pharmaceuticals, and cosmetics. Besides being hygroscopic and solvent capable, it is also used industrially as an antifreeze and coolant because of its properties.

The following uses are commonly associated with propylene glycol:

• As a humectant in processed foods
• As pharmaceuticals, injectable, and topical preparations 
• In personal care, such as moisturizers, shampoos, and conditioners
• As anti-freeze, paint, and e-cig liquid products.

Dipropylene Glycol

Dipropylene glycol (DPG) is a secondary product of the hydration of propylene oxide, normally held in conjunction with the manufacture of propylene glycol itself. Because of its relatively high molecular weight and inferior volatility, it can find applications more suited to instances where less penetration in the skin and evaporation are required, such as in perfumes and some industrial formulations.

DPG is, however, usually found in:

• As a solvent in fragrance formulations for essential oils
• In the formulations of personal care products, such as deodorants and lotions
• Industrial cleaning agents
• Solvents for inks and hydraulic fluids for use in printing

So,  is dipropylene glycol the same as propylene glycol? From their common origin in propylene oxide, it can be seen that they would have some structural similarities; however, the two substances’ properties and applications differ greatly.

Chemical Differences Between Dipropylene Glycol and Propylene Glycol

Structural Composition

The major chemical distinction is their molecular structures. Propylene glycol contains a single propane backbone and two hydroxyls, whereas dipropylene glycol is a mixture of isomers containing two propane units bridged with an ether link. This makes the molecular weight significantly higher and thicker for DPG.

Physical Properties

• Viscosity: Due to the higher viscosity of DPG compared to PG, this has also affected its handling and flow properties in formulations. 

• Boiling Point: The boiling point of DPG is more than that of PG, i.e., over above 230°C compared to 188°C of PG; thus, DPG becomes an appropriate solvent for high-temperature applications.

• Solubility: Both are miscible with water and several organic solvents but, in addition, PG is mostly miscible with oils. 

• Volatility: PG, being more volatile, performs better in situations when fast drying is required. DPG, which has a higher evaporation rate, is ideal for long-lasting products such as perfumes and air fresheners. 

Thus, these differences are mainly responsible for their functions in the products, and, therefore, one must understand the differences between dipropylene glycol vs propylene glycol during the formulation stage.

Applications in Personal Care Industry

Propylene Glycol in Personal Care

Propylene glycol is one multifunctional agent. It acts as a humectant, solvent, and emulsifier. It promotes the absorption of active ingredients into the skin and helps maintain the stability of the preparation. 

Applications include:

• Moisturizers & Creams: Provide hydration to the skin from the surrounding environment.
• Deodorants and Antiperspirants: Help dissolve active ingredients and facilitate absorption into the skin. 
• Hair Care Products: Provides conditioning properties and moisture retention in hair strands. 
• Makeup Products: Provides for an even distribution of pigments and prevents drying.

Dipropylene Glycol in Personal Care

It is low-volatility, mild, and compatible with fragrances that are probably why DPG is predominantly in such kinds of formulations. 

Applications as listed below: 

• Perfumes & Fragrances: DPG is used as a carrier of essential oils because of its mild odor and slow evaporation. 
• Skin Lotions & Creams: Soft velvety texture and a dispersant action for dispersed ingredients. 
• Color Cosmetics: It is to dissolve pigments and ensure uniform application. 
• Deodorants & Body Sprays: This gives stability and better compatibility with the fragrances. 

In short, DPG is collection charming sensory experience or sustained fragrance discharge, while PG is for deep hydration and delivery of active ingredients. 

Also Read: Locust Bean Gum in Food Manufacturing: Applications & Sourcing Considerations

Applications in Industrial & Technical Use

Propylene Glycol in Industrial Applications

Industrial Environment: Because of its hygroscopic and less toxic nature, PG can be used in systems where humans periodically come in contact with the systems. 

Common Applications Are:

• Antifreeze & De-icing Fluids: Its application is in aircraft de-icing or the low-temperature freeze point along with automotive antifreeze.
• Hydraulic Fluids: This makes PG fit for water-based hydraulic systems due to its lubrication properties.
• Heat Transfer Fluids: It has application in food processing, as well as in pharmaceutical industries due to incidental contact issues.
• Paints & coatings: It functions as a solvent or viscosity reduction.

Dipropylene Glycol in Industrial Applications

With its high boiling point and great solvent capacity, DPG is suitable for any application requiring stability and prolonged performance.

Some common applications involve: 

• Plasticizers in polymers: Enhances flexibility in plastics and lowers brittleness.
• Solvent for printing inks: Maintains ink consistency and allows adhesion on different surfaces.
• Industrial cleaners: Provides solvency without rapid evaporation.
• Deodorant and air fresheners: Suitable for formulations requiring slow evaporation and mild fragrance.

Dipropylene glycol is more niche than propylene glycol, whose applications may range anywhere from household to industrial, having properties not too dissimilar from the dipropylene glycol counterpart: low volatility and prolonged interaction.

Health and Safety Considerations

Toxicity and Skin Sensitivity

Glycols as a class are fairly nontoxic. In particular, propylene glycol has been studied extensively and approved for use in food and pharmaceutical applications. It may, however, irritate some sensitive individuals, especially in higher concentrations. 

Dipropylene glycol is safe for topical use, but is not approved for food use. Skin sensitivity irritation is less associated with this glycol, which is why it enjoys use in perfumes and body-care formulations.

Regulatory Approvals

• Propylene Glycol: A substance GRAS (Generally Recognized As Safe) for ingestion by the U.S. FDA having been included in the list of permitted food additives of the European Union, E1520. 

• Dipropylene Glycol: Not approved for ingestion but widely recognized under IFRA and REACH regulations for cosmetic and industrial uses. 

Environmental Impact

Both glycols are biodegradable and have low persistence in the environment. PG is especially prized for its low toxicity to aquatic organisms, making it ideal in areas where disposal of waste water is of concern. DPG, while harmless to the environment, is less commonly employed for disposal in mass commercial use.

Choosing the Right Glycol for Your Business

The decision about dipropylene glycol vs propylene glycol involves the following factors:

• Application Requirements: Propylene Glycol is best suited for food-grade, pharmaceutical, and personal care products having the most moisture-requiring formulations. DPG is better suited for fragrance concentration and industrial and high-heat applications.

• Regulatory Compliance: Propylene Glycol is the natural case for all consumables or pharmaceuticals because it is approved by the FDA. Dipropylene glycol is more applicable in topical and industrial uses in which ingestion will not occur.

• Performance Characteristics: If the key requirements are quick absorption and low viscosity, PG would be your better choice. If the requirement is a longer-lasting carrier with much lower volatility, then DPG will prevail.

• Cost and Availability: The fiesty PG keeps costs down and is readily available for large-volume applications. DPG capabilities have justifiably a higher price in niche formulations. 

Understanding the nuances of propylene glycol versus dipropylene glycol helps to ensure that your product both performs well in the field and meets regulatory and consumer expectations.

Also Read: What is Hydrochloric Acid Used For? Key Applications in Industry and Everyday Life

Conclusion: Make Smarter Formulation Choices with Elchemy

Propylene glycol and dipropylene glycol are not the better alternatives. They are rightly selective. While PG provided excellent hydration, solubility, and great acceptable for consumables with regulatory approval, DPG with a low odor and high boiling point as well as emollient properties makes an excellent carrier for fragrances and industrial solvents.

When classifying the difference you would find that it helps to formulate better and safe and economical for people who manufacture in line with personal care, pharmaceuticals, or industrial formulations.

Accompany Elchemy as your partner in sourcing high-quality dipropylene glycol and propylene glycol. Our robust global network, stringent quality controls and technical expertise ensure you get the best ingredients for your specific needs.