Weathering of Artificial Grass Yarn CEN TC 217 WG 11, 18/10/2016 Daniel Müller (BASF) & Jeroen Wassenaar (TOTAL)

Transcription

1 Weathering of Artificial Grass Yarn CEN TC 217 WG 11, 18/10/2016 Daniel Müller (BASF) & Jeroen Wassenaar (TOTAL)

2 Why doing Artificial Weathering? Simulation of the photooxidative behavior of polymers Purpose: Development of new products and applications, screening Long term outdoor weathering for reproduction of environmental influences needed Accelerated weathering for screening purposes Get insight on quality of a product Quality of production Index tests given by standardization Properties to be evaluated Mechanical properties for functionality Visual properties for aspect Requirements: Representing reality Reproducible test method Economic for supplier and end user

3 Solar Radiation UV Radiation of the wave length: below 175nm is absorbed by oxygen in the atmospheric layers more than 100km above surface between 175 and 290nm is absorbed by ozone layer of the stratosphere (max density: ~25km) between 290 and 400nm reaches the surface Only the UV Radiation of the wave length between 290 and 400nm reaches the surface and is potentially able to initiate degradation of plastics

4 Photooxidation Photooxidation is initiated by the action of photons onto the plastic article Photooxidative degradation results from the combined action of light and oxygen The degradation process proceeds analogous to the autoxidation cycle + + = PHOTOOXIDATION

5 Without Light, no Photooxidation 1 st Law of photochemistry (Grotthus Draper): Only the part of light effectively absorbed by a substance leads to photochemical degradation 2 nd law of photochemistry (Stark Einstein): For each photon of light absorbed by a chemical system, no more than one molecule is activated for a photochemical reaction «Low wavelength UV light (<290 nm) enables transitions that are not accessible in real life, leading to photochemical reactions that do not naturally occur on earth» Jablonski diagram of optical transitions: Solid lines: radiative transitions between states Wavy lines: vibrational relaxations processes (vr) and radiationless transitions (IC = internal conversion / ISC = intersystem crossing)

6 Wave Length Sensitivity of Plastics Polymer degradation is wave length dependent UV light affects different polymers differently Polyolefins absorb UV light due to oxidation products formed during processing or by impurities present in the polymer. Engineering resins and rubbers absorb UV light due to their intrinsic chemical structure (e.g. Polystyrene, Polyesters..)

7 Geographical Distribution of Sun Ray Energy Various climate conditions depending on the regions Different further factors to be considered beside sun ray energy: humidity, day and seasonal fluctuations, altitude, pollution, : Florida (Miami): standard, fairly constant climate Arizona (Phoenix): dry / hot climate, high irradiation Bandol (France): moderate climate, most sun hours in Europe Hainan Island (China): humid subtropical

8 Artificial Weathering Different settings possible, potentially influencing the result (variety of standards in the industry) Examples of setting parameters: radiation energy, wet/dry cycle, temperature, humidity, Widest use in the industry

9 Artificial Weathering Various Specifications to be met: WOM spectrum in line with UV radiation reaching the Earth QUVA spectrum fitting UV radiation in the low wavelength area QUVB spectrum only in very low wavelength area and far below 290nm

10 Protection of Polymers from Degradation Screeners UV screeners, examples: Fillers Carbon black Pigments However: Metal containing pigments can catalyze formation of free radicals Reflected light can concentrate UV energy on the surface Some fillers may absorb and/or react with stabilizers

11 Protection of Polymers from Degradation Screeners Pigments Pigment act as light manager Pigments also absorb in the visible. Heat (energy) can additionally build up depending on color and may influence the durability of the whole system

12 Protection of Polymers from Degradation UV Absorbers Protect the bulk of materials Light is absorbed Intensity of light decreases exponentially Bulk material is well protected, however surface might degrade Law of Lambert Beer: A = e. c. d = log I0/I Absorbance = Molar Absorptivity Concentration Path Length

13 Protection of Polymers from Degradation Hindered Amine Light Stabilizers (HALS) Protect the bulk and surface of materials HALS molecules are active in the whole sample, they protect: Surface (light stability) Bulk (light and thermal stability)

14 Evaluation of Weathering Effects

15 Failure Criteria: Visual Aspects White appearance can be due to Polymer degradation on the surface Fading of the pigment Polymer still intact

16 Artificial Compared to Natural Weathering PE Films Florida / QUVB Florida / WOM Linear correlation r 2 = 0.36 Linear correlation r 2 = 0.96 LDPE blown films 200 m; T 0.1 = time to 0.1% carbonyl absorbance E 50 = energy to 50% retained elongation LDPE blown films 200 m; T 50 = time to 50% retained elongation E 50 = energy to 50% retained elongation WOM (Xenon Arc) weathering with good correlation QUVB (Fluorescence Arc) weathering without correlation

17 Artificial Compared to Natural Weathering PE Tapes hours QUVB hours WOM hours WOM kly HDPE tapes, 50 m, different formulations; hours resp kly to 50% retained tensile strength hours QUVB Correlation with Florida WOM good QUVB very limitied kly

18 Comparison of Different Artificial Light Exposure LLDPE Monofilaments QUVA with similar behavior compared to WOM QUVB with highest impact on degradation

19 Comparison of QUVA with QUVB in LLDPE Yarns* 100% 5 Retained tensile strength 90% 80% 70% 60% 50% UVA 3000 UVA 5000 UVB 3000 Colour change grey scale UVA 3000 UVA 5000 UVB 3000 Average from 7 monofilaments for sports turf Tensile strength not significantly affected by any aging method after required time frame => no polymer degradation Colour change more severe with UVA after measurement with proposed new test method (UVA, 5000h) => better simulation of effect of solar radiation on colour * tested by Kiwa ISA Sport

20 Summary Polymers can undergo degradation when exposed to sunlight Influence of UV radiation from nm Influence of environmental conditions Accelerated weathering to be done under realistic conditions Wave length sensitivity of different plastics Different ways to protect resins Different degradation mechanism depending on the UV wave length applied Different artificial weathering methods for accelerated testing QUVA and WOM measurement similar to real life UV radiation QUVB only covering very low wave lengths and goes below 290nm simulating unrealistic conditions for life time considerations

21 Conclusion QUVA 5000h is the proposed accelerating weathering method for artificial turf applications: Covers a large part of the critical UV light Keeps radiation at wave lengths > 290nm Provides reasonable acceleration Easily accessible in the market and in testing institutes Extension of the standard to be fulfilled in CEN and already accepted by most of the stakeholders in the market Representing reality Reproducible test method Economic for supplier and end user QUVA QUVB WOM

22 ANNEX

23 Solar maximum in different locations* Cleveland Kitt Peak Miami * From Q-Lab technical bulletin LU-0822