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Research on gypsum based humidity controlling materials


									    Research on gypsum-based humidity controlling materials
                              JIANG Hong-yi,             LUAN Cong-mei
      (School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 , China)

                       Abstract: Absorption/desorption properties of some humidity controlling
                  materials which contain gypsum as basic cement materials and activated Sepiolite
                  powder as humidity controlling media are tested in this text. The kinetics curve of
                  moisture adsorption/desorption are drawn and humidity controlling performance in
                  nature environment is verified. The results show that moisture
                  absorption/desorption rates are increasing, and the speed is also accelerated. These
                  materials, which can adjust environmental humidity effectively, are new ones with
                  good humidity controlling performance.
                       Key words: Activated Sepiolite; Gypsum-composites; Humidity controlling

1 Introduction                                           2.1 Materials and preparation
      Humidity controlling materials are                      Sepiolite powder is dried at 100℃ and
environmental materials which can control                reserved. Prepare CaCl2 solution and then
ambient relative humidity automatically [1].             mixed with dried Sepiolite powder, in which
When relative humidity exceeds a specific                the quantity proportions of Sepiolite and CaCl2
range, they will absorb moisture, when relative          are 8:1, 8:2, 8:3 and 8:4 separately. Stir the
humidity is lower than a specific range, they            mixture until it is homogeneous, and dry it at
will release moisture so as to increase ambient          110℃. The samples prepared are marked as
humidity. The relative humidity in system can            S+C1, S+C2, S+C3 and S+C4. Sepiolite is S.
be kept constant effectively by their                         Gypsum-composite humidity controlling
absorption/desorption      performance        [2]
                                                 .       materials are prepared by adding S+C1 or
Semi-hydrate gypsum owns the advantage of                S+C2 to semi-hydrate gypsum in proportion of
lightweight, insulation, sound absorption and            10%, 15% and 20%. After formed, samples are
non-combustible. What’s more, gypsum                     removed from moulds and dried for 5 h at 50℃,
productions have higher air permeability due to          which marked as A1, A2, A3 and B1, B2, B3.
their large porosity and proper pore size                And then put them in the environment of 20℃
distribution. Building gypsum, mixed with                and 40%RH for maintenance。
activated Sepiolite powder are prepared and              2.2 Performance evaluation and testing
their absorption/desorption kinetics are studied               Absorption/desorption performance of
in this text.                                            humidity controlling materials are tested by
                                                         static absorption method depicted in
2 Experimental
                                                         International Organization of Standardization
                                                         (ISO) 12571[3] (measurement of building
                                                         materials and production’s damp-heat and
Wuhan University of Technology
Received: April 20, 2010 Accepted: May 8, 2010           absorption performance).
JIANG Hongyii: E-mail:
                              3 Results and discussion                                                        moisture absorption rate are: S-12.36%,
                              3.1      Absorption/desorption         moisture                                 S+C1-71.38%, S+C2-118.71%, S+C3-124.32%
                              performance of activated Sepiolite powder                                       and S+C4-142.14% separately. After activated
                                   The kinetics curve of moisture                                             by CaCl2, the amounts of adsorption and
                              adsorption/desorption [4] are shown in Fig 1 and                                desorption for sepiolite are both improved, and
                              Fig 2.                                                                          will increase with the content of CaCl2
                                                                                                              increasing     . Sepiolite owns a porous and
                                                                                                              loose structure. In the environment of high
                                               S+C1                                                           humidity, water can be adhered to these pore
moisture absorption rate(%)

                                               S+C3                                                           walls, and physical absorption appears; calcium
                                                                                                              chloride     can   react    with    water   and
                                                                                                              chemisorption takes place. At the same time,
                                                                                                              Sepiolite’s pores can work as water containers
                                                                                                              for calcium chloride to absorb more water.
                                                                                                              These two kinds of absorption are carried out

                                       0        20         40      60   80        100   120   140     160
                                                                                                              simultaneously and congenerously.
                                                                   time(h)                                          During experiment it has been observed
                                                                                                              that some samples will be wetted during
                                    Fig . 1 Adsorption kinetics of water vapor at
                                                25℃ and 97%RH                                                 absorption. Table 1 lists that the comparison
                                                                                                              between the amounts of water uptake before
                                                                                                              wetted and final moisture absorption rates. It
                                                                                                              can be seen that S+C3 and S+C4 are wetted
moisture releasing rate(%)

                               -20                                                                            seriously, and their pores can not undertake all
                               -40                                                                            water absorbed.
                                                                                                              3.2        Absorption/desorption       moisture
                                                                                                              performance of gypsum-based humidity
                               -80             S
                                               S+C1                                                           controlling materials
                              -100             S+C2
                                               S+C3                                                                 Dry gypsum samples for 24 h at 50℃ and
                                                                                                              put them into circumstance of 25℃, 97% RH
                                           0          20           40        60         80      100

                                                                    time(h)                                   for absorption. After saturated, the samples are
                                                                                                              removed into circumstance of 25℃, 11% RH
                               Fig . 2 Desorption kinetics of water vapor at
                                                                                                              for releasing moisture. The results are list in
                                            25℃ and 11%RH
                                                                                                              Table 2 and the kinetics curve of moisture
                                                                                                              adsorption/desorption are shown in Fig 3 and
                                      It can be seen that samples’ saturated
                                                                                                              Fig 4

                                                                Table 1 The amount of water uptake before wetted and after wetting
                              Samples                                                                 S        S+C1         S+C2         S+C3       S+C4
                              Final absorption rates/%                                                12.36    71.38        118.71       124.32     142.14
                              The water uptake before wetted/%                                        12.36    71.38        107.57       96.79      88.65


  moisture absorption rate/%

                                                                                                           moisture absorption rate/%
                               20                                                                                                          30

                               10                                               A1                                                         15                                                    B2
                                                        Table 2 Adsorption ration of water vapor of compoties samples
                                                                                B1                                                                                                               C2
                                                                                C1                                                         10
Samples                                                                        A1                 A2           A35                                                 B1                B2                         B3
Absorption rate/%                                                              22.39              23.11        27.66
                                                                                                                 0                                                 29.3              35.84                      38.6
        0    20  40                                         60        80         100       120    140               0                                    20        40  60     80   100
Desorption rate/%                                                time/h
                                                                               -11.3              -11.87       -16.47                                              -16.95    time/h
                                                                                                                                                                                       120                  160   180


  moisture absorption rate/%

                                                                                                              moisture absorption rate/%
                               20                                                                                                          30

                               10                                               A1                                                         15                                                    B2
                                                                                B1                                                                                                               C2
                                                                                C1                                                         10


                                     0       20        40   60        80        100        120    140                                            0       20        40   60   80     100        120    140   160    180
                                                                 time/h                                                                                                      time/h

                                                        Fig 3 Adsorption kinetics of water vapor of gypsum composites

                                0                                                                                                           0
  moisture releasing rate/%

                                                                                                           moisture releasing rate/%

                                -5                                                   B1                                                                                                          A2
                                                                                     C1                                                                                                          B2
                                                                                                                                           -10                                                   C2




                                         0        20        40            60          80         100                                                 0        20        40     60         80          100    120
                                                                 time/h                                                                                                      time/h

                                                        Fig 4 Desorption kinetics of water vapor of gypsum composites
     Fig 3 indicates that composite samples still                                                          desorption rate is as much as final desorption
have good absorption moisture performance.                                                                 rate’s 60%. After 48 h, it is more than final
The amount of water absorption will increase                                                               desorption rate’s 70%. The sample with highest
with the increasing amount of activated                                                                    desorption amount can be balanced in 6 days.
Sipiolite. The responsive character of                                                                     3.3 Humidity controlling in nature condition
composite samples is also excellent. After                                                                       Put 40 g of sample B3 into a hexahedral
absorbing for 24 h, the water uptake rate is                                                               box       with      inside     dimension       of
more than saturated rate’s 34%. After 48 h, it is                                                          52cm×28cm×50cm. The box is left an air
more than saturated rate’s 61%. The sample                                                                 opening in a side; therefore the condition inside
with highest absorption amount can be                                                                      is same as that outside before humidity
saturated in 9 days.                                                                                       controlling materials are put in it. Two
     Fig 4 indicates that the samples’ releasing                                                           temperature     and      humidity    monitoring
speed is also fast. After desorbing 24 h, the                                                              instruments are placed inside and outside
separately. They can monitor the change in                                                               temperature and humidity of two different
conditions       simultaneously.   Humidity                                                              water absorption/desorption will increase with
controlling performance is analyzed and the                                                              the increasing amount of activated Sipiolite.
result is shown in Fig 5.                                                                                      (3) In nature environment, the selected
                                                                                                         sample can control relative humidity in a
                                                                                                         satisfied    range.    The    requirement     of
                                80                                                                       performance and quantity foe humidity
temperature/relative humidity

                                70                                                                       controlling materials may be different
                                                                                                         according to the climate and air flowing, which
                                                                                                         needs to be further studied.
                                                        relative humidity outside
                                40                      relative humidity inside

                                                                                                         [1] Z. W. Jiang.The research progress of
                                       23:12:00   11:12:00   23:12:00   11:12:00   23:12:00   11:12:00

                                                                                                               humidity       controlling       materials[J].
                                                                                                               Materials Review, 2006, 10: 8-11.
                                Fig 5 The capability of B3 with 40 g in 72 h
                                                                                                         [2] A. V. Arundel, E. M. Sterling, J. H. Biggin.
                                                                                                               Indirect health effects of relative humidity
      Fig 5 shows the case of humidity
                                                                                                               in indoor environment[J]. Environmental
controlling material B3 for 72 h. It can be seen
                                                                                                               Health Perspectives, 1986 (65): 351-361.
from Fig 5 that during this time, the range of
                                                                                                         [3] ISO12571 The measurement of building
relative humidity outside is 58.4%-82.3%RH,
                                                                                                             materials and production’s damp-heat and
while the range of relative humidity inside is
                                                                                                             absorption performance[J].            Thermal
59% - 62.8% RH. The ability of humidity
                                                                                                             insulation material and energy-saving
controlling for samples is sustaining.
                                                                                                             technology, 2000 (1): 23-25.
                                                                                                         [4] M. Y. Ran, J. J. Yuan. The test method of
4 Conclusion
                                                                                                             moisture       absorption/desorption        for
      (1) After activated by CaCl2, the amounts                                                              humidity controlling materials[J]. Heating
of adsorption and desorption for sepiolite are                                                               ventilating air conditions, 2006, 4 (36):
both improved, and will increase with the                                                                    10-16.
content of CaCl2 increasing.                                                                             [5] F. Caturla, S. M. Molina. Rodriguze R.F.:
      (2) The absorption/desorption capacity and                                                             Adsorption-desorption of water vapor by
responsive      character   of    gypsum-based                                                               natural and heat-treated sepiolite in ambient
composite are substantially improved when it is                                                              air[J]. Applied Clay Science, 1999 (15):
mixed with activated Sepiolite. The humidity                                                                 367-380.
controlling performance of samples is closely
related to activated Sepiolite: the amount of

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