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.

2 Experiments

2.1 Raw materials

2.1.1 Cement

P.042.5 ordinary silicate cement produced by Shanghai Seal Cement (Group) Co.

2.1.2 Sand

The sand is fine sand with a fineness modulus of 1.82 and a bulk density of 1480k/m3

2.1.3 Cellulose ether

Hydroxypropyl methyl cellulose produced by Gomez Chemical (China) Co., white solid powder, viscosity 75000mP/s, 100000mP/s respectively.

2.1.4 Mixing water

Tap water was used for the mixing water.

2.2 Test programme

2.2.1 Matching ratio determination

The experiment uses three kinds of ash-sand ratio, namely 1:3, 1:4 and l:5, and the amount of hydroxypropyl methylcellulose is 0-0.2% of the cement dosage. The amount of mixing water was determined according to the flow rate of the fresh mortar, and the flow rate of all mortars was controlled within the range of 160sh5mm.

2.2.2 Mortar preparation and testing

Firstly, the accurately weighed hydroxypropyl methylcellulose is mixed with the cement. Then mix with the sand for 30s, then add the mixing table water and mix for 3rain according to the "Cement Sand Strength Test Method" (GB/T17671.1999), and measure the flow of the fresh mortar according to GB24t9--200|: according to JGJ70.90 "Basic Performance Test Method of Building Mortar" to determine the flow of fresh mortar. Determination of the bulk density and setting time of the mortar: Determination of the water retention of the fresh mortar according to German standard DINl8555-7. The water reduction rate is calculated with reference to "Concrete Admixtures" (GB8076-1997), i.e. when the mortar flow rate is 160 sh5ram, the difference between the water consumption per unit volume of the base mortar and the water consumption per unit volume of the cellulose ether-doped mortar is compared with the water consumption per unit volume of the base mortar.

2.2.3 Net mortar making and testing

The cement was mixed with water-cement ratio without hydroxypropyl methylcellulose and corresponding to three kinds of ash-sand ratio, namely O.73, 0.9, 1.21 (Table 5) according to JGJ70.90 "Basic Performance Test Methods for Building Mortar", and then its bulk density was measured.

3 Results and discussion

3.1 Water reduction rate

Gomez chemical experiments show that in the case of a certain ratio of gray sand, with the increase in the amount of hydroxypropyl methyl cellulose, water reduction rate are gradually increased, that is to say, in this test range (cellulose ether doping Ying.2%) cellulose ether has a certain water reduction effect, the reason is mainly due to the bearing effect of the air bubbles introduced by the admixture of polymer. At the same time can be found: mix M1 when the water reduction rate rose to the greatest extent, and mix M3 when the water reduction rate rose to the smallest extent, which shows that the greater the viscosity of cellulose ether water reduction effect is more obvious. In the case of the same viscosity of hydroxypropyl methyl cellulose, the smaller the ash-sand ratio, the weaker the water reduction effect, but not significant.

3.2 Water retention

The experiments show that the water retention rate of mortar decreases significantly with the decrease of ash-sand ratio when it is not mixed with hydroxypropyl methyl cellulose. After mixing with cellulose ether, the change of water retention rate of mortar has two characteristics, one is that it increases with the increase of cellulose ether, and the larger the viscosity, the higher the water retention rate. The second is that its increase increases with the decrease of ash-sand ratio. To mix M1, for example, the ash-sand ratio of l:3, not mixed with cellulose ether water retention rate of 82.3%, and mixed / x.o.2% cellulose ether, water retention rate of up to 1J98.9%, an increase of about 16%: ash-sand ratio of l:4. Water retention rate of 78.1% without cellulose ether, water retention rate of 98 after mixing A.0.2% cellulose ether, an increase of about 20%; and ash-sand ratio of 1:5, water retention rate of 72.3% from cellulose ether to 98.3% with 0.2% cellulose ether, an increase of about 25%.

3.3 Bulk density

The experiment shows that when not mixed with hydroxypropyl methyl cellulose, the bulk density of fresh mortar decreases with the decrease of the ash-sand ratio. Obviously, this is related to the net density of cement in fresh cement mortar, sand bulk density and its dosage. When the ash-sand ratio decreases, the water-ash ratio rises and the density of the corresponding net cement mortar also decreases, while the sand bulk density is close to the density of net cement mortar when the ash-sand ratio is l:5, so the bulk density of the fresh mortar decreases with the decrease of the ash-sand ratio. After mixing with cellulose ether, the bulk density of mortar decreases significantly with the increase of cellulose ether, and the greater the viscosity, the more obvious the effect. This is because cellulose ether has a certain air-entraining effect, and the higher the viscosity the more air-entraining, and the more obvious the air-stabilising effect, thus reducing its density. When comparing different ash-sand ratios, it is found that the decrease in bulk density increases with the decrease in ash-sand ratio under the same viscosity of cellulose ether.

3.4 Setting time

The experiments showed that the setting time of the mortar was significantly prolonged with the decrease of the ash-sand ratio when it was not mixed with hydroxypropyl methyl cellulose. After mixing with cellulose ether, the change of mortar setting time has two characteristics: firstly, it is prolonged with the increase of cellulose ether, and the smaller the viscosity of cellulose ether, the longer the suspicious setting time: secondly, its increase increases with the decrease of grey sand ratio.

4 Conclusion

(1) In the range of 0.1%-0.2% of hydroxypropyl methyl cellulose, the changes of water reduction rate, water retention, bulk density and setting time of fresh cement mortar are not only related to the viscosity and dosing of cellulose ether, but also depend on the ash-sand ratio.

(2) The water reduction rate gradually increases as the amount of hydroxypropyl methyl cellulose increases, and the greater the viscosity, the more obvious the water reduction effect. In the case of the same viscosity of cellulose ether and dosing, the smaller the ash-sand ratio, the weaker the water reduction effect.

(3) The water retention rate of mortar decreases significantly with the decrease of ash-sand ratio when not mixed with hydroxypropyl methyl cellulose. After mixing with cellulose ether, the water retention rate of mortar increases with the increase of the amount of cellulose ether, and the increase of the mortar increases with the decrease of the ratio of grey to sand.

(4) The bulk density of mortar decreases with the decrease of ash-sand ratio when it is not mixed with hydroxypropyl methyl cellulose. After mixing with cellulose ether, the bulk density of mortar decreases with the increase of cellulose ether dosing, and the greater the viscosity, the more obvious the reduction effect. At the same time, the bulk density decreases with the decrease of grey to sand ratio.

(5) When the mortar is not mixed with hydroxypropyl methyl cellulose, the setting time of the mortar is significantly prolonged with the decrease of the ash-sand ratio. After mixing with cellulose ether, the change of mortar setting time also has two characteristics, one is that it is prolonged with the increase of cellulose ether, and the other is that its increase is increased with the decrease of grey to sand ratio.