Q.U.V. EXPOSURE     |     SEPAP TESTING

Background

 

The long-term use of polypropylene composites in outdoor or exposed conditions is very dependent on the resistance of the polypropylene resins to ultraviolet light. The polypropylene resin in Twintex® is designed to be U.V. resistant and is well suited for outdoor applications. Long-term exposure to direct sunlight is the only true test to determine the performance of a material in outdoor applications, but the test may take several years to complete. A Q.U.V. accelerated weathering tester was used to determine the relative U.V. resistance of Twintex®.

 

Experimental

 

> Material

 

Material	Product	Color	% Glass	Thickness
Twintex®	2 Plies	Black	60%	2.5 mm
	T PP 60 1485
Twintex®	2 Plies	Natural	60%	2.5 mm
	T PP 60 1485

 

> Sample Preparation

 

Twintex® samples were prepared by molding two layers of 1485g/m2 Twintex® fabric and one layer of 745g/m2 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 stack 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 3 75mm x 225mm were cut from the Twintex® molded plates.

 

 

> Test Specifications

A Q.U.V. accelerated weathering tester equipped with UVB-313 lamps was used to perform the test in accordance with ASTM D4329-84. The cycle was alternating eight hours of U.V. exposure at 60°C and four hours of condensation at 50°C. Test specimens were exposed on one side to U.V. radiation. Multiple specimens from each material were used in the test and removed at periodic intervals for evaluation.

 

 

> Correlation to Outdoor Exposure

A direct correlation of Q.U.V. to outdoor exposure does not exist, and any empirical correlation needs to be used with caution. In a paper published by George Grossman titled, "Correlation of Laboratory to Natural Weathering," Journal of Coating, March 1977, empirical data was generated over a wide range of materials comparing Q.U.V. to natural weathering. Based on this paper, he concluded that on average, one hour of Q.U.V. equals 17 hours of natural radiation. This factor varied from 8:1 to 25:1, depending on the material being tested.

 

 

 

Twintex® Natural Q.U.V. Exposure

 

 

 

Twintex® Black Q.U.V. Exposure

 

A Xenon Arc Weatherometer was used to determine the relative U.V. resistance of Twintex®. The test was performed in accordance with ASTM G-26. The cycle alternated between 102 minutes of U.V. exposure at 63°C and 18 minutes of U.V. exposure with a water spray. The light was 340 nm with an energy density of 0.35 watts/m2. Test specimens were exposed on one side to U.V. radiation. Multiple specimens from each material were tested and removed at intervals of 500 hours, 1,000 hours, 1,500 hours, 2,000 hours, 3,000 hours and 4,000 hours for evaluation.

 

 

Twintex® Natural Xenon Arc Exposure

 

 

 

Twintex® Black Xenon Arc Exposure

 

ARIZONA DESERT TESTING

Background

 

The long-term use of polypropylene composites in outdoor or exposed conditions is very dependent on the resistance of the polypropylene resins to ultraviolet light. The polypropylene resin in Twintex® is designed to be UV-resistant and is well suited for outdoor applications. Long-term exposure to direct sunlight is the only true test to determine the performance of a material in outdoor applications. Twintex® panels were exposed in the Arizona desert for an extended period of time under three different exposure conditions. The three different conditions simulate unbacked exposure applications such as truck roofs, backed exposure such as cored panels and under glass exposures such as automobile interiors.

 

Experimental

 

> Material

 

 

Material	Product	Color	% Glass	Thickness
Twintex®	T PP 60 1485	Black	60%	4 mm
Twintex®	T PP 60 1485	Natural	60%	4 mm

 

 

> Sample Preparation

Twintex® samples were prepared by molding four layers of 1485g/m2 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 stack 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 125mm x 300mm were cut from Twintex® molded plates.

 

> Test Specifications

ASTM G7-96 Unbacked: test is performed at a tilt angle of 45°From horizontal facing south, with specimens mounted with open backing.
ASTM G7-96 Backed: Test is performed at a tilt angle of 45°From horizontal facing south, with specimens mounted on 12.5mm MDO plywood.
ASTM G24-94 Method B: Test is performed at 5°From horizontal, facing south with specimens mounted under glass in an enclosed black cabinet. The cabinet is equipped with filtering vents and continuously operating recirculating fans to minimize temperature variations within the cabinet. Specimens are mounted on a galvanized steel wire cloth frame.

> Results

 

Flexural Modulus Unbacked Results (MPa)

 

 

 

 

		Exposure Time
		3 months	6 months	9 months	12 months
Natural	Warp	11,487	11,220	10,652	10,599
	Weft	10,700	12,085	12,204	11,889
Black	Warp	11,325	11,502	10,937	10,691
	Weft	12,027	11,331	12,428	12,176

 

Backed Results (MPa)

 

 

 

 

		Exposure Time
		3 months	6 months	9 months	12 months
Natural	Warp	11,100	10,961	10,562	11,162
	Weft	12,271	12,101	12,619	11,772
Black	Warp	10,468	10,373	10,599	10,771
	Weft	12,303	13,231	12,232	11,48

 

Under Glass (MPa)

 

 

 

 

		Exposure Time
		3 months	6 months	9 months	12 months
Natural	Warp	11,518	10,367	10,226	11,930
	Weft	12,775	11,731	12,084	12,358
Black	Warp	11,034	10,861	10,738	10,510
	Weft	12,892	11,578	11,835	12,349

 

 

Unbacked Results (MPa)

 

 

 

 

		Exposure Time
		3 months	6 months	9 months	12 months
Natural	Warp	276	241	238	244
	Weft	237	259	266	252
Black	Warp	290	291	249	247
	Weft	273	260	274	270

 

 

 

Backed Results (MPa)

 

 

 

 

		Exposure Time
		3 months	6 months	9 months	12 months
Natural	Warp	232	270	258	245
	Weft	265	262	285	240
Black	Warp	271	241	256	251
	Weft	292	304	290	272

 

Under Glass (MPa)

 

 

 

 

		Exposure Time
		3 months	6 months	9 months	12 months
Natural	Warp	253	245	233	246
	Weft	177	251	261	263
Black	Warp	269	259	246	251
	Weft	299	264	278	271

 

> Conclusion

After one year in the Arizona desert, all but one set retained more than 90% of the original strength and stiffness. The flexural strength after unbacked exposure is the exception. Both natural and black specimens retained more than 80% of the original flexural strength in the warp direction, and 100% in the weft direction.

 

One possible cause for this is that weft fibers are "buried" by the warp fibers; hence, protecting the interface between the weft fibers and the PP material. During fabric construction, the warp fibers are woven about the warp fiber to make the fabric. As a result, the warp fibers are "sinusoidal," and the weft fibers are "linear."

 

 

 

Twintex® Natural - Arizona Desert Test - Exposed open backed at 45° 

 

 

 

Twintex® Black- Arizona Desert Test - Exposed open backed at 45° 

 

 

Twintex® Natural - Arizona Desert Test - Exposed backed at 45° 

 

 

 

Twintex® Black- Arizona Desert Test - Exposed backed at 45° 

 

 

 

Twintex® Natural - Arizona Desert Test - Exposed under glass 5° from horizontal 

 

 

 

Twintex® Black - Arizona Desert Test - Exposed under glass 5° from horizontal