Test method for water retention of hydroxypropyl methylcellulose ether HPMC

Hydroxypropyl Methyl Cellulose ether is one of the most commonly used additives in dry mortar. Hydroxypropyl methyl cellulose ether plays an important role in dry mortar, after the cellulose ether within the mortar is dissolved in water, it ensures an effective and uniform distribution of the cementitious material in the system due to the surface activity, while hydroxypropyl methyl cellulose ether acts as a protective colloid that “wraps “This makes the mortar system more stable and also improves the fluidity of the mortar during mixing and the smoothness of the construction. The cellulose ether solution, due to its own molecular structure characteristics, makes the water in the mortar not easily lost and gradually released over a longer period of time, giving the mortar good water retention and workability. The water retention of hydroxypropyl methyl cellulose ether is the most important and basic indicator. Water retention refers to the amount of water retained by a newly mixed mortar on an absorbent substrate, after capillary action. The water retention test of hydroxypropyl methyl cellulose ether has no relevant national testing methods, and manufacturers usually do not provide technical parameters, which brings inconvenience to users and judges, we Gomez Chemical based on years of experience in dry mortar, with reference to the test methods of other products, summarized the following test methods of water retention of cellulose ether, for discussion.

I. Evacuation method

Water in the slurry after filtration

The method is based on JC/T517-2005 “stucco” industry standard, the test method is based on the original Japanese standard (JISA6904-1976). The test is carried out by filling a Brønsted funnel with water, placing it on a filtering bottle, turning on the vacuum pump and pumping for 20 min under a negative pressure of (400±5) mm Hg, and then calculating the water retention rate according to the water volume in the slurry before and after filtering.

Water retention (%) = ( water in slurry after filtration / water in slurry before filtration ) × 100

The water retention rate is measured by the evacuation method, which is more accurate and has less error, but requires special instruments and equipment, which is a big investment.

Filter paper method

The filter paper method is used to judge the water retention of Hydroxypropyl Methylcellulose Ether by the water absorption of the filter paper. It consists of a metal ring mould of a certain height, filter paper and glass pallets, with 6 layers of filter paper underneath the mould, the first of which is fast filter paper and the remaining 5 layers are slow filter paper. A precision balance is used to weigh the pallets and the 5 layers of slow filtration paper, then the mortar is mixed and poured into the test mould and scraped flat and left for 15 minutes; the pallets and the 5 layers of slow filtration paper are then weighed. Calculate according to the following formula.

M = (m1 – m2)/S

M — Water loss, g/ mm2

m1 – weight of pallet + 5 layers of slow filter paper; g

m2 — weight of pallet + 5 layers of slow filter paper after 15 min; g

S—- area of the test mould mm2

It is also possible to directly observe the degree of water absorption of the filter paper. The lower the water absorption of the filter paper, the better the water retention. The test method is easy to operate, and general enterprises can meet the experimental conditions.

Three, surface drying time test method.

The method can be referred to GB1728 “Method for the Determination of Drying Time of Paint and Putty Film”, where the mixed mortar is scraped onto an asbestos cement board and the thickness is controlled at 3mm.

Method I. Cotton Ball Method

Place a skimmed cotton ball on the surface of the mortar and at certain intervals, blow the ball along the horizontal direction with the mouth 10-15cm away from the ball, if it can be blown away and no cotton wool remains on the surface of the mortar, the surface is considered dry.

Method 2: Finger touch method

Gently touch the surface of the mortar with clean fingers at certain intervals, if you feel some stickiness, but no mortar on the fingers, the surface is considered dry, the longer the interval, the better the water retention. The above methods, the filter paper method and the finger touch method are more commonly used and easier; users can initially judge the water retention of hydroxypropyl methyl cellulose ether from different manufacturers through the above methods; as there is no relevant standard, the above methods are provided by Teng Yuan Chemical for reference.

Influence of viscosity of hydroxypropyl methylcellulose ether and grey to sand ratio on the performance of freshly mixed cement mortar

Dry-mixed mortars are extremely superior in terms of quality, efficiency, economy and environmental protection. Hydroxypropyl methylcellulose is an important additive in dry-mixed mortars, which mainly acts as a water retainer. Although the amount of hydroxypropyl methylcellulose added is very low, it can significantly improve the performance of the fresh mortar, such as increasing the compatibility, making the mortar less susceptible to water secretion and separation, making it easy to work in thin layers, and it can also improve the impermeability and frost resistance of the hardened mortar.

Many scholars have studied the effect of hydroxypropyl methylcellulose on mortar properties, but the influencing factors mainly focus on the amount of hydroxypropyl methylcellulose and viscosity, while little has been reported on the mortar ratio. In this paper, the physical properties of fresh cement mortars with three different ash-sand ratios are investigated, and the difference in the viscosity of hydroxypropylmethylcellulose at low dosing levels is observed.