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PVA Sponge Dimension Expansion Rate

Marking on Ciruclar PVA sponge roller
Marking on Circular PVA sponge roller

Many aware that the PVA sponge does expand after retains with water but not many discussed about the expansion rate. Even though the PVA sponge will expand after fully soak in water unfortunately not many talk about the expansion rate. The pore shrink at dry form, once the pore is filled with water, the entire PVA sponge expanded.

How much PVA sponge will expand while fully soak in water? 3%, 5% or 10%

Water Retention

The PVA sponge product favor in retaining water, in our previous article, PVA sponge water retention ability, we had pointed out that a PVA sponge could able to withhold 9-11 times of it own weight of water amount. Hence, a fully soaked PVA sponge will expand and causing a minor changes in the dimension.

Measurement Method

Marking on the PVA block sponge
Marking on the PVA block sponge

Since the sponge is a soft material, sometime it is hard to measure the exact dimension with the contact method. For user who requires accurate reading, we always recommend none contact type of measurement method. In this case, using an optical inspection equipment is a good choice.

PVA Sponge Expansion Amount

In this testing, we want to examine the expansion rate for various moisture content. This give us a better understanding about the dimension fluctuation due to various moisture level. In the below chart, we are given the dimension change rate base on 2 moisture level, namely 2x and 6x moisture level.

PVA Sponge Roller Expansion Rate

There are some minor change in the higher moisture level such as 8x and even 10x moisture level but during the handling stage, a small amount of water will be accidentally squeeze out. We think that 2x-6x moisture level will be more practical way for handling the PVA sponge under wet form. Again this is not the hard requirement standard.

From the data, we could experience 5-10% expansion at wet stage compare with drys stage. Further more, the more water content, the PVA sponge will have additional 1-2% expansion compare with 2x moisture.

The Impact of Dimension Expansion

Now we have the expansion rate collected from various sponge either on the diameter or the length. In most cases, there is a inner core inserted in the PVA sponge roller and a layer of adhesive apply to prevent slippery. In other words, the inner diameter and length is fixed.

From the above diagram, the sponge outer diameter expansion variation is contributed by 2 factors:

  1. The difference of various sponge sample. There are about 3% variation due to sample’s variation. The 3% variation is contributed due to sponge expansion due to water retention.
  2. The difference causes by various sponge moisture. The difference moisture or water content within the sponge also causing minor expansion, from the data, it shows about 1.5% variation.

Let assume we are having a PVA sponge and this sponge is experiencing the maximum variation. This means the sponge may experience as large as 4.5% variation! For a 60mm diameter roller, the 4.5% variation means that this particular sponge is experiencing 2.7mm shifted from the “exact” diameter value.

If we only consider the diameter changes due to various sponge moisture, we may experience additional 1.5% expansion in outer diameter. Again, for a 60mm diameter sponge roller, this implies that 0.9mm shifted in diameter data.

The PVA Sponge dimension is having huge variation after soaked in water.

From the above data, we learn the PVA sponge expansion variation due to various water retention level. The difference of expansion rate also contributes in larger dimension variation and perhaps this is the nature of the PVA sponge.

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