There are many classifications of Hydroxypropyl methylcellulose (HPMC). According to its uses, Landercoll® Hydroxypropyl methylcellulose (HPMC) can be divided into two categories, surface treated HPMC and non-surface treated HPMC. And today, let’s talk about the differences between the 2 types. Before talking, we have to know the different names of the two types. Surface-treated HPMC is also called instant type,delayed solubility/ hydration HPMC. Non-surface treated HPMC is also known as hot soluble type and slowly soluble HPMC.
How to make the surface treated HPMC？
Compared with ordinary HPMC, the production of surface-treated HPMC has one more process. We use a cross-linking agent (usually use glyoxal) to treat its surface. The purpose of this step is to enable HPMC to disperse quickly in cold water, rather than dissolving at the beginning. If the added amount of glyoxal is large, the dispersion will be fast, but the viscosity will rise slowly. If the added amount is small, then the situation will be the opposite. It is this extra process that makes the price of surface-treated HPMC higher than the non-surface treated type.
How to dissolve these two types of HPMC (Hydroxypropyl Methyl Cellulose)? What is the specific method?
Cold-water instant soluble HPMC (Surface treated) can rapidly disperse in cold water. But it will not dissolve at this step, so the liquid has no viscosity because HPMC is only dispersed in water and there is no real dissolution. About 2 minutes, by even stirring, it will dissolve and the viscosity of the liquid gradually increased to form a transparent viscous colloid. Hot-soluble type(Non-surface treated), lumped in cold water, but when it mixes with hot water, it will quickly disperse. By stirring, until the temperature drops to a certain temperature (In our company, the gel-forming temperature of the resulting product is around 65°C-75°C), the viscosity slowly appears until a transparent viscous colloid is formed.
The reason for lumping in the cold water is that the outer cellulose powder encounters cold water, immediately starts to have a viscosity, thickens into a transparent colloid, and the cellulose inside is not in contact with water, and is surrounded by the colloid, or is powdery, but slowly dissolves. Here it should be noted that many users think hot-water soluble HPMC must rely on hot water, which is one-sided. In practical applications, the non-surface treated hydroxypropyl methyl cellulose (HPMC) is mainly applied in dry-mixed mortars such as mortar and putty. And it is not necessary to use hot water to dissolve hot-melt products, because the putty powder or mortar is powder. After dry mixing, the cellulose is separated by other materials, and there will be space between cellulose. Thus when it meets water, it will immediately become viscosity and will not have lumps.
Hot soluble type (Non-surface treated) HPMC dissolution methods
If the hot soluble type (Non-surface treated) HPMC is added directly to the water, agglomeration will occur before dissolution. However, dissolving in this way is very slow and difficult. Here we recommend three dissolution methods for end-users based on different applications：
- 1. Hot water dissolution method: Since HPMC is not dissolved in hot water, the initial HPMC can be uniformly dispersed in hot water and then rapidly dissolved upon cooling. Two typical methods are as follows:
Add the required amount of hot water in the container and heat it to about 70°C. Hydroxypropyl methylcellulose(HPMC) was gradually added with slow stirring, and the HPMC floated on the surface of the water, and then gradually formed a thick liquid, and the thick liquid was cooled with stirring..
Adding 1/3 or 2/3 of the required amount of hot water(70°C) to the vessel, gradually add HPMC to hot water and keep stirring. The remaining amount of cold water was then added to the hot thick liquid and continued stirring until the mixture cools.
2 . Powder mixing method: Mix the HPMC powder with a large amount of other powdery substances, mix well with a blender, and then add water to dissolve. At this time, HPMC can be dissolved without agglomeration, because each tiny small corner has only a little HPMC. The powder will dissolve immediately upon contact with water. – This is the method used by putty powder and mortar manufacturing.
3 . Organic solvent humidification dissolution method: HPMC is pre-dispersed or wetted with an organic solvent such as ethanol, ethylene glycol, or oil, and then dissolved in water, and HPMC can be easily dissolved.
Instant type (Surface treated) HPMC dissolution methods
Surface treatment powders are specially developed to prevent lumping in wet-mixing applications such as paint and emulsion applications. In order to prepare a solution from the surface-treated powder, the powder is directly placed in cold water. Over time, a fully developed solution of suitable viscosity was prepared by continuously stirring the solution.
Note: In order to dissolve quickly, the instant type (Surface treated) HPMC will dissolve rapidly after adjusting PH value to 8-10 by adding ammonia or alkali water, forming a solution.
NON-SURFACE TREATED HPMC
In short, for different types of products, the correct method can be fully dissolved. If agglomeration occurs during dissolution, it is caused by insufficient agitation or direct addition of ordinary models to cold water. At this time, it should be stirred quickly. In addition, if bubbles are generated during dissolution, it can be left to stand or defoamer added.
Non-surface treated HPMC
As we talked about before, the hot-dissolved type (Non-surface treated) is mainly applied in putty powder and mortar. By applying dry and even mixing, the HPMC in the resulting mixture will become separated by other materials. The viscosity will immediately build up after adding water and the resulting product will not clump together.
In liquid glue and paint, there will be lumped. In contrast, it is available in a wide range of applications for instant type (Surface treated), in putty powder and mortar, as well as in liquid glues and coatings. There are no contraindications. However, for instant type (Surface treated), its water retention and stability are not comparable to hot soluble type (Non-surface treated). Therefore, we recommend hot soluble types in dry powder such as putty powder and mortar.
Surface treated HPMC
Compared to the non-surface treated HPMC, the instant type (Surface treated) HPMC has a wider application area. It can be used in ash calcium-based putty and cement-based mortar, as well as in glues and coatings. Under an alkaline condition, the instant type HPMC can achieve a certain calibrated viscosity. In a gypsum-based mortar, due to the acidic pH value of gypsum, the delayed solubility of hydroxypropyl methyl cellulose (HPMC) will only become viscous very slowly.
The initial setting of construction-grade gypsum can be achieved in or more than 3 minutes. Yet, the final set can only be formed in or less than 30 minutes. Although a certain amount of retarder is required in the gypsum-based mortar to delay the time of setting, the operating time of the resulting gypsum-based mortar is still not as good as the cement-based and gypsum-based products. So, some alkaline materials must be added to increase the time of the HPMC becoming viscous.