Hydroxypropyl Starch Ether (HPS)

Product Characteristics

1. Appearance

• Industrial/Construction Grade: White or off-white powder, odorless and tasteless
• Food/Pharmaceutical Grade: Pure white fine powder, uniform particle size
• Particle size can be adjusted according to application, commonly 80–200 mesh

2. Core Structural Features

The molecular structure of HPS involves the introduction of -CH₂CH(OH)CH₃ (hydroxypropyl) substituents at the C2, C3, and C6 positions of the starch glucose unit. Key indicators include:

• Molar Substitution (MS): The average number of moles of hydroxypropyl groups bound to each glucose unit
• Low MS (<0.1): Limited solubility in cold water, requires heating for gelatinization
• Medium MS (0.1–0.3): Soluble in cold water, most widely used
• High MS (>0.3): Excellent solubility in cold water, high stability
• Substitution uniformity: Affects the product's dissolution rate and solution transparency

Physicochemical Properties

1. Solubility

• Cold Water Easily soluble (medium to high MS products), forms a transparent or translucent colloidal solution
• Hot Water Easily soluble, viscosity slightly lower than cold water
• Organic Solvents (ethanol, acetone, etc.) Insoluble or limited swelling
• High-Concentration Electrolyte Solutions Good stability, less prone to salting out (advantage of non-ionic solutions)

2. Solution Characteristics

• Viscosity Characteristics: Moderate solution viscosity, mild thickening effect, usually lower than the equivalent concentration CMC
• Thixotropy/Pseudoplasticity: Exhibits shear-thinning properties, smooth during application, and recovers its structure after standing.
• Transparency: High transparency; MS product solutions exhibit excellent transparency.
• Film-forming properties: Forms a flexible, biodegradable film after drying.
• Water retention: Effectively locks in moisture, preventing the substrate from drying too quickly.

3. Chemical Stability

• pH Range | Stable within pH 3–11, wide applicability
• Thermal Stability | Stable at normal operating temperatures; prolonged high-temperature heating may cause viscosity decrease.
• Electrolyte Tolerance | Excellent – ​​non-ionic structure, unaffected by polyvalent cations.
• Enzyme Stability | Superior to native starch, but still slowly degraded by amylases.
• Freeze-Thaw Stability | Good, not prone to stratification or water separation due to repeated freeze-thaw cycles.

4. Other Important Properties

• Nonionicity: Does not undergo charge neutralization reactions with anions/cations, excellent compatibility.
• Biodegradability: Derived from natural starch, completely degraded by microorganisms, environmentally friendly.
• Low Calories/Hypoallergenicity: Food-grade product suitable for special dietary needs.
• Emulsification Auxiliary Function: Synergistically stabilizes emulsions with surfactants
• Adhesion: Moderate adhesion strength, suitable for various substrates

Product Classification

Classification by Raw Material Source

• Corn Starch-Based HPS | Low cost, high output, versatile
• Cassava Starch-Based HPS | Good transparency, delicate texture, commonly used in food grade
• Potato Starch-Based HPS | High viscosity, good film-forming properties
• Waxy Corn Starch-Based HPS | High amylopectin content, high viscosity, good anti-aging properties

Classification by Application Area

• Food Grade | Meets food standards | Food additives, thickeners and stabilizers
• Pharmaceutical Grade | High purity | Pharmaceutical excipients, sustained-release carriers
• Construction Grade | Industrial standards | Dry-mixed mortar, putty, tile adhesive
• Daily Chemical Grade | Cosmetic standards | Skin care products, detergents
• Paper Grade | Industrial standards | Surface sizing, coating

Classification by Viscosity

• Low Viscosity: 5% solution viscosity < 100 mPa·s
• Medium viscosity: 5% solution viscosity 100–2000 mPa·s
• High viscosity: 5% solution viscosity > 2000 mPa·s

Main Applications (by Industry)

1. Construction Industry ⭐ (Largest Application Area)

HPS is most widely used in dry-mix mortars, often used in conjunction with cellulose ethers (such as HPMC, HEMC):

• Putty Powder:
• Improves workability, making application smoother
• Increases adhesion between putty and substrate
• Reduces cellulose ether usage, lowering costs
• Tile Adhesive/Tile Bonding Agent:
• Enhances water retention, extending open time
• Improves anti-slip properties, preventing tile slippage
• Increases bond strength
• Plastering Mortar/Masonry Mortar:
• Retains water and thickens, preventing excessive water absorption by the substrate
• Improves mortar workability and operability
• Self-Leveling Mortar:
• Adjusts rheology, controlling bleeding and segregation
• Improved Surface Smoothness
• Gypsum-Based Products:
• Delays Gypsum Setting Time
• Improves the Surface Finish of Gypsum Products

> Synergistic Effect: When HPS is compounded with HPMC/HEMC, HPS provides lubricity and workability, while cellulose ethers provide water retention and thickening properties. The two complement each other, resulting in excellent cost-effectiveness.

2. Food Industry

HPS is an internationally recognized food additive with high safety:

• Seasonings/Sauces:
• Thickening and stabilizing of ketchup, salad dressing, and mayonnaise
• Preventing oil-water separation and solid sedimentation
• Dairy Products:
• Stabilizer in yogurt and milkshakes, preventing whey separation
• Improves melt resistance and texture in ice cream
• Baked Goods:
• Improves texture and delays aging in bread and cakes
• As a humectant, extending shelf life
• Convenience Foods:
• Anti-freezing cracking and water retention in instant noodles and frozen foods
• Thickening of instant soup mixes and seasoning packets
• Candy/Jelly:
• Texture improvement in gummies and gel candies
• Adjusting transparency and elasticity of jellies
• Low-Calorie Foods: As a fat substitute, providing a fat-like texture

3. Pharmaceutical Industry

• Tablet Excipients: As a binder, disintegrant, or diluent
• Capsule Filler: Improves powder flowability
• Sustained-release formulations: Used as a matrix material to control drug release
• Ointments/creams: Thickening and moisturizing base
• Oral liquids/suspensions: Stabilizing suspension systems

4. Daily Chemicals/Cosmetics

• Skincare products:
• Thickening and stabilizing agents for face creams and lotions
• Film-forming and moisturizing agents for face masks
• Viscosity modifiers for facial cleansers
• Shampoos/shower gels: Adjusting viscosity and improving foam texture
• Detergents:
• Thickening and stabilizing liquid detergents
• Anti-fouling redeposition

5. Paper industry

• Surface sizing: Improves paper strength, smoothness, and printability
• Coatings: Used as adhesives and water-retaining agents
• Wet-end addition: Improves fiber retention and paper evenness

6. Textile printing and dyeing industry

• Warp sizing: Improves yarn abrasion resistance and weaving efficiency
• Printing pastes: Used as dye carriers to control penetration
• Fabric finishing: Imparts a soft hand feel and antistatic properties

7. Petroleum Industry

• Drilling Fluids: As a filtration reducer and thickener
• Fracturing Fluids: Thickening and proppant carrying
• Completion Fluids: Adjusting rheological properties

8. Other Applications

• Agriculture: Seed coating agent, pesticide suspension stabilizer
• Ceramics: Body reinforcement, glaze slurry suspension
• Adhesives: Thickening and water retention of water-based adhesives
• Water Treatment: Partial flocculation applications

Brief Description of Production Process

HPS production mainly involves the following steps:

1. Raw Material Preparation: Selecting natural starch (corn, cassava, potato, etc.), controlling moisture and impurities
2. Slurry Preparation: Dispersing starch in an alkaline aqueous solution or organic solvent
3. Alkalization: Adding sodium hydroxide to swell starch granules and activate hydroxyl groups
4. Etherification: Adding propylene oxide (PO) to undergo an etherification reaction with starch under alkaline conditions
5. Neutralization: Neutralizing excess alkali with acid
6. Washing: Wash with water or organic solvents to remove byproducts (propylene glycol, sodium chloride, etc.)
7. Drying/Pulverizing/Sieving: Obtain the finished powder
8. Packaging: Package according to grade requirements

Safety and Regulations

• Toxicity: HPS is derived from natural starch, is non-toxic, non-irritating, and non-carcinogenic.
• ADI: The FAO/WHO Joint Expert Committee sets the ADI for food-grade HPS at "No Special Requirements"
• Regulations:
• Permitted by China's GB 2760 "Standards for the Use of Food Additives"
• Approved by the US FDA GRAS
• Approved as a food additive by the European Union
• Allergens: Individuals with cereal allergies should be cautious with products derived from corn/wheat.

Summary

Hydroxypropyl starch ether (HPS) is a naturally derived, high-performance, low-cost, and environmentally friendly non-ionic water-soluble polymer material. Its core advantages are:

1. Non-ionic properties – strong electrolyte tolerance and excellent compatibility
2. Cost advantage – significantly lower price than cellulose ether products
3. Workability – provides excellent lubricity and workability
4. Biodegradability – completely biodegradable and environmentally friendly

HPS plays a crucial role in modern industry as a functional additive in dry-mixed mortars. Through synergistic compounding with cellulose ethers, it achieves the dual goals of performance enhancement and cost control. Simultaneously, its applications in food, pharmaceuticals, and daily chemicals are continuously expanding, making it a green high-potential material.