effect of surrounding conditions on paper properties
TRANSCRIPT
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
1/31
Effect of Surrounding Conditions
on Paper Properties
Standard Conditions of Measurement
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
2/31
Strength and Surrounding Conditions
Strength of paper may be affected very significantlydue to variation of temperature and relativehumidity of atmosphere
Consequences :- Paper/board suitable at one place may
not serve the same purpose at another
place and may fail.
- Measurement of properties at some
specified temperature and RH conditions.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
3/31
Variation of moisture content in paper due to
temperature and RH of atmosphere.
Effect on fiber-fiber bonding due to moisture
content in paper
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
4/31
Variation of moisture content is
due to hygroscopic nature of
cellulose fiber
25-65% RH
-1% increase per 10%
change in RH
RH>65%, faster increase
RH~100%,- Moisture ~ 27-30%
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
5/31
Moisture Content vs Conditioning Time
Rate at which paper achieves moistureequilibrium depends upon :
- Type of fiber,
- Process conditions e.g. pulping, beating etc.
- degree of sizing,
- type and amount of coating,
- basis weight,
- type and amount of fillers.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
6/31
Effect of conditioning time on equilibrium moisture in 60 lbkraft paper. Conditioned from (A) 35-85% RH (B) 85-35% RH
Moisture content changes very rapidly at first and thenslows down.
Time to reach equilibrium moisture content- 15 minutes for lightweight papers
- 24-48 hours for paper board and heavily sized papers
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
7/31
Measurement of Moisture Content
Most common is Drying Method.
Dry a weighed specimen in a circulating air ovenat 105C.
Moisture content =wt. loss on drying(gm)x100/original wt.(gm)
On a cold winter day, oven has low humidity. Thisresults in 0.51% higher moisture content than
on a hot, humid, summer day. Vacuum removes 0.51% more moisture than an
ordinary oven.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
8/31
Basis Weight Variation
Increased moisture content, due to enhanced
RH conditions, increases basis weight.
Normally, Moisture content ~ 6-7%
Change in basis weight varies from paper to
paper and depends upon
- Type of fibers and process conditions.- Type and amount of fillers
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
9/31
RH, % -cellulose
and rag paper%
Average
Papers%
Groundwood
Papers%
20 -1.5 -2.5 -3.3
30 -1.0 -2.0 -2.7
40 -0.5 -1.0 -1.3
50 0 0 0
60 +0.5 +0.7 +1.2
65 +1.0 +1.5 +2.2
70 +1.7 +2.5 +3.7
75 +2.5 +4.0 +5.2
80 +3.5 +5.0 +7.2
Basis Weight Variation with Moisture Content
(w.r.to 50% RH Value)
1. Least variation in rag pulps due to lowest amount of hemicellulose
2. Highest variation in Groundwood due to highest amount of hemicellulose
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
10/31
Consider a bond paper of 80 gsm.
At 50% RH, its moisture content will be 6%
On taking it to 80% RH (hot and humid environment
i.e. places near sea shores)
Increase in basis weight 5% i.e. 5% of 80 = 4 gsm
Or This bond paper will now have 84 gsm basis weight
Considering this aspect one can sell this paper at a higher
cost with around 6% less fiber whereas actually
this paper will not give any advantage of paper with
higher basis weight e.g. improved strength, opacity, stiffness
In fact, all these properties will deteriorate (on account of less
fiber content and deterioration in above props with higher
moisture content.)
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
11/31
Effect on various strengthparameters due to variationin Relative humidity
Stretch - increases Burst- TS and stretch
foldTS and flexibility
Tearhigher fr. of fibers
come out after breakingfiber bonds
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
12/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
13/31
Specifications for Measurement
BIS RH = 652%, Temp.=272C
Sample conditioning
- RH=25-35%,Temp.=40C,Time=24hrs
Condition at BIS specified conditions
- Time ~ 4 hours (normal paper)
- Time ~ 24 hours (hard sized papers)
Difference between successive weighing
< 0.25% measured at an interval of 1 hour
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
14/31
Ex:
For a sheet (22x30 cm) of 70 gsm
Weight of sheet = 4.6 gm 0.25% of weight of sheet = 0.01gm
Weight 4.64.61 gm (indication of
conditioned sheet)
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
15/31
After conditioning :
Paper should not be kept near
- Window (avoid sunlight)
- Radiator (avoid heat)
- Open space during rainy season
Not touched by hands (to avoid grease and moisture
Avoid water marks, edges, fold, crease, torn part
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
16/31
Tissue and Towelling
Tissue products e.g. toilet tissue and towels
are sold in roll form (in some cases with
perforations provided for separating small
pieces from roll).
Term sheet has no relevance in these cases.
Important is the Roll from which portion of
material for testing is being taken.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
17/31
Sampling
Tissues have high level of creping, to improvepliability and compressibility.
They get stretched easily when test pieces are
prepared which in turn affects the properties oftissue.
When preparing test pieces from rolls, theproduct be unrolled while supported by laying it
on a lab bench. Pulling sheets vertically from a suspended roll
must be avoided to minimize stretching.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
18/31
Conditioning (curing)
Tissue products have wet strength, which in turn isprovided by adding wet strength chemicals in pulpfurnish.
Wet strength is achieved after these chemicals aregiven sufficient time for ageing/curing which could varyfrom few minutes to several weeks for different wetstrength chemicals.
Recently manufactured tissue products, therefore, be
cured before they are tested for different properties.
Measured properties will be indicative of thoseexperienced while the product is in use.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
19/31
Curing is done by exposing the sample at highertemperature for a specified duration.
It is simply a process by which paper manufacture
determine the wet strength performance ofpaper several days/weeks before the paper isused.
(paper maker would like to determine the
possible performance of the product severalweeks after the manufacture, by measurement
just after paper has been made)
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
20/31
Generally for curing the conditions are :
SCAN-57
Temperature 80C, Time 30 min or 24 hour European Std. EN 12625-5
- Temp. 80C, Time 30 min or
- Temp. 105, Time 15 min (for productioninspection to enable correction, if required)
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
21/31
Important Consideration :
To determine the properties of tissue product,
as experienced by the end user on product
purchased from store, test the sample without
curing (The store sample is likely to have been
manufactured at-least few weeks earlier so no
need for curing)
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
22/31
Ageing Characteristics
Determines whether a paper sample will age
more rapidly as compared to others.
Important for record papers, ledgers, map etc. In
general any paper which is meant to keepdata/records for long duration.
The effect of ageing is due to breaking of fiber-
fiber bonds due to gradual drying of sample in airwith time. This results in deterioration of strength
of paper. Ultimately paper becomes brittle.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
23/31
The aging characteristics of paper is determinedby finding decrease in double fold value of asample when it is given aging treatment.
The aging process is simulated by heating papersample at a temperature varying between 60125C.
Change of temperature by 20C alters rate ofdeteroration by a factor of 7.5. Accelarated aging
temp. must be rigorously controlled. In addition, the paper moisture content must be
held constant during accelerated aging.
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
24/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
25/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
26/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
27/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
28/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
29/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
30/31
-
8/12/2019 Effect of Surrounding Conditions on Paper Properties
31/31