7-Day Water Boil Test

 

Conclusion

 

Twintex® shows exceptional resistance to boiling water. Compression-molded plates absorbed less than 0.8% water and retained 85% of the flexural strength and 95% of the original dry flexural modulus. The consolidated sheets absorbed almost 4% water, which is expected due to the higher porosity of this material processed using very low pressures.

 

Background

Many composite applications require a material that is resistant to hot, wet environments. Twintex®, which combines two very water-resistant materials - glass and polypropylene, is a good candidate for these applications. Samples of Twintex® were placed in boiling water for seven days to test the resistance of Twintex® to hot, wet environments.

 

Experimental

 

> Material

 

 

Material	Product	Color	% Glass	Thickness
Twintex®	T PP 60 1485	Black	60%	3.7 mm
	(molded from fabric)
Twintex®	T PP 60 1485	Natural	60%	3.7 mm
	(molded from fabric)

 

> Sample Preparation

 

The first two sets of Twintex® samples were prepared by molding four layers of Twintex® fabric. The fabric was placed between two, thin stainless-steel platens and heated in a 210°C press at a pressure of 5 Bars. When the middle of the fabric reached 205° C, the platens and fabric were transferred to a cold press and cooled to room temperature under 15 Bars pressure. Test specimens of 25mm x 75mm were cut from each of the molded panels.

 

> Test Specifications 

 

A water boil test was performed in accordance with ASTM D570. Because of the inherently good water resistance of the materials, the length of the test was extended to seven days. Multiple specimens from each material were removed after one, two, six and seven days. Samples were weighed, and the percent water absorption was measured. Flexural tests (ASTM D790-92) were performed on unexposed samples, and the samples that were exposed to the water boil for seven days.

Weight Gain (%) of Specimens in Boiling Water

 

 

 

	% of Weight Gain
Material	1 Day	2 Days	6 Days	7 Days
60% Black Molded	0.41%	0.57%	0.67%	0.72%
60% Natural Molded	0.47%	0.57%	0.74%	0.79%

 

Flexural Strength After 7-Day Water Boil

 

 

Flexural Strength (MPa)
Material	Initial	7 Days	% Retention
60% Black Molded	300	251	84
60% Natural Molded	281	242	86

 

Flexural Modulus After 7-Day Water Boil

 

 

Flexural Strength (MPa)
Material	Initial	7 Days	% Retention
60% Black Molded	13,411	12,758	95
60% Natural Molded	13,048	12,401	95

 

 

> Long-term Water Absorption Properties of Twintex® - Conclusion

 

Both black and natural Twintex® exhibit excellent long-term exposure resistance to ambient water. A minimal amount of water was absorbed over the first 8 weeks, and then stabilized at approximately 0.35% water gain. The flexural strength and modulus were unaffected by the exposure to water over the entire test period.