Weathering of Artificial Grass YarnCEN TC 217 WG 11, 18/10/2016
Daniel Müller (BASF) & Jeroen Wassenaar (TOTAL)
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
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 reachesthe surface and is potentially able to initiate degradation of plastics
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
Without Light, no Photooxidation
– 1st Law of photochemistry (Grotthus‐Draper):• Only the part of light effectively absorbed by a substance leads to photochemical degradation
– 2nd 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
Jablonski diagram of optical transitions:Solid lines: radiative transitions between statesWavy lines: vibrational relaxations processes (vr)
and radiationless transitions (IC = internal conversion / ISC = intersystem crossing)
« 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 »
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..)
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
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
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
Protection of Polymers from DegradationScreeners
– 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
Protection of Polymers from DegradationScreeners ‐ 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
Protection of Polymers from DegradationUV 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/IAbsorbance = Molar Absorptivity ∙ Concentration ∙ Path Length
Protection of Polymers from DegradationHindered 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)
Evaluation of Weathering Effects
Failure Criteria: Visual Aspects
– White appearance can be due to• Polymer degradation on the surface
• Fading of the pigment• Polymer still intact
Artificial Compared to Natural WeatheringPE Films
– WOM (Xenon Arc) weathering with good correlation– QUVB (Fluorescence Arc) weathering without correlation
Florida / QUVB Florida / WOM
Linear correlationr2 = 0.96
Linear correlationr2 = 0.36
LDPE blown films 200 m;T50 = time to 50% retained elongationE50 = energy to 50% retained elongation
LDPE blown films 200 m;T0.1 = time to 0.1% carbonyl absorbanceE50 = energy to 50% retained elongation
Artificial Compared to Natural WeatheringPE Tapes
– Correlation with Florida• WOM good• QUVB very limitied
kLy
kLy
hours WOM
hours QUVB
hours WOM
hours QUVB
HDPE tapes, 50 m, different formulations;hours resp kLy to 50% retained tensile strength
Comparison of Different Artificial Light ExposureLLDPE Monofilaments
– QUVA with similar behavior compared to WOM– QUVB with highest impact on degradation
Comparison of QUVA with QUVB in LLDPE Yarns*
– 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
0
1
2
3
4
5
UVA 3000 UVA 5000 UVB 3000
Colour cha
nge ‐grey scale
50%
60%
70%
80%
90%
100%
UVA 3000 UVA 5000 UVB 3000
Retained
tensile
strength
Summary
• Polymers can undergo degradation when exposed to sunlight– Influence of UV radiation from 290‐400nm– 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
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
QUVA QUVB WOM
Representing reality
Reproducible test method
Economic for supplier and end user
ANNEX
Solar maximum in different locations*
* From Q-Lab technical bulletin LU-0822
Cleveland
Kitt Peak
Miami