Glycerin is a universal basic raw material across various industries. It achieves multiple functions such as locking moisture, moisturizing, thickening, and dissolving through its hydrophilic hydroxyl structure. It is widely used in daily skin care products, medicines, baked foods, and mechanical processing. The following text comprehensively explains the basic properties, raw material sources, safety standards, full-range applications, and key points for selecting and purchasing at different levels of glycerin. 

I. Basic Definition and Physical-Chemical Properties of Glycerol

Glycerol is chemically known as propylene glycol, with the molecular formula C₃H₈O₃. At room temperature, it is an odorless, transparent, viscous liquid with a slight sweet taste. It can be freely mixed with water and ethanol in any proportion. It has a high boiling point and is not prone to freezing at low temperatures. Its hydrophilic group can firmly lock water molecules, which is the core source of its moisturizing and water-retaining properties. 

There are three preparation routes: natural oil hydrolysis extraction, chemical propylene synthesis, and biological fermentation. Different processes result in significant differences in the purity and impurity content of glycerol, and they need to be matched with the corresponding application scenarios. 

II. Sources and Grades of Glycerol

Natural Glycerol: Obtained from the saponification of palm oil and animal fats, with low impurities, mainly used in high-end products such as food, cosmetics, and medicine;

Chemical Synthesized Glycerol: Produced by the oxidation and hydrolysis of propylene, with large output and low cost, divided into high-purity and ordinary industrial specifications;

Biological Fermentation Glycerol: Obtained through microbial conversion of starch raw materials, environmentally friendly, the demand in the organic cosmetics and food sectors is increasing year by year.

The industry is divided into three grades based on purity, and the uses are strictly distinguished and cannot be mixed: Pharmaceutical grade ≥ 99.9%, Cosmetics grade ≥ 99.5%, Industrial grade 70%-95%, and the control standards for heavy metals and microorganisms are gradually relaxed. 

III. Safety Instructions for Glycerol Use and Contact

The high-purity glycerol is non-toxic and low in irritation. It has been recognized as a GRAS (Generally Recognized As Safe) material by multiple countries and can be safely used in food and oral preparations. 

Usage Notes: 1. The 99% high-concentration pure glycerin should not be directly applied to the skin. It will absorb the skin's natural oils in reverse, causing dryness. It needs to be mixed with water for use. 2. Taking a large amount at one time may cause abdominal distension and diarrhea. Food additives follow national standard limits. 3. Industrial-grade glycerin has excessive impurities and must not be used in skincare or food intake scenarios. 4. For sensitive skin and infant products, choose cosmetics-grade glycerin that has undergone skin irritation tests.

Four, Four Core Industry Application Scenarios

1. Cosmetics and Skincare Field

Classic basic moisturizing raw material, adsorbing moisture from the air to repair the skin barrier. Added to face creams, lip balms, essences, body lotions, with a regular addition amount of 5% - 20%, improving dryness and peeling. 

2. Pharmaceutical Preparation Industry

Colace's core raw material softens feces; it is used as a solubilizer for oral liquids and syrups; it is a base for suppositories and topical ointments, being gentle and non-irritating and suitable for mucosal administration. 

3. Food Processing Industry

Food-grade glycerin serves as a moisturizer, sweetener, and anti-aging agent. It helps delay the hardening of starch in bread and pastries, and regulates the taste and sweetness of candies and beverages, conforming to the additive standards of GB 2760. 

4. Industrial Manufacturing Field

Mechanical lubrication, coolant antifreeze, tobacco humidification, textile paper moisture retention, ink viscosity adjustment. Only industrial-grade glycerin is permitted for use. 

V. Key Points for Purchase and Use

First, determine the corresponding grade based on the usage scenario: for oral intake and injection preparations, choose pharmaceutical grade; for facial skin care, select cosmetic grade; for mechanical anti-freezing lubrication, choose industrial grade. Avoid mixing grades that are not compatible. Review the product test report and carefully check the indicators of heavy metals, moisture, and purity to ensure the safety of use. 

Due to its versatile physical and chemical properties, glycerol has found applications in both consumer goods and industrial manufacturing. With the development of green bio-based raw materials, the market share of fermented glycerol continues to increase. Only by using it in a compliant and graded manner can its value be fully realized while risks of safety can be avoided.