Comparison of naturally and artificially weathered wood-polymer composites: An algorithm-based approach Dipl.Ing., Dipl.Ing., B.Sc., M.B.A. Daniel Friedrich Compolytics Independent Research, Neunkirchen, Germany Lecturer at Baden-Württemberg Cooperative State University of Mosbach, Germany Lecturer at the SRH University of Heidelberg, Germany MC Member and Communication Manager of COST ACTION CA16114 d.friedrich@lehre.mosbach.dhbw.de Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 1
Contents 1. Wood-Polymer Composites (WPC) 2. Comparison between natural and artificial weathering 3. Computing of WPC ageing 4. Summary Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 2
1. Wood-Polymer Composites (WPC) 1.1 WPC Components: Petrochemical or bio-based thermoplastics (PP, PE, PVC) + Wood fibers + Additives = WPC Fig. 1 : WPC composition. Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 3
1. Wood-Polymer Composites (WPC) 1.2 WPC Applications in the Building Scope: Currently all WPC products are petrochemical-based Flooring Decking Cladding Source: www.upm.com Fencing Fig. 2 : WPC applications. Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 4 4
2. Comparison between natural and artificial weathering 2.1 Artificial versus natural weathering: WPC strength-decrease is measured by: Change in Modulus of Rupture (MOR) [MPa] Change in Modulus of Elasticity (MOE) [MPa] Natural weathering trials (EN 15534-1): Depend on climate zone Mix of UV radiation, frost/thaw, wet/dry periods Fig. 3: Global climate zon es. Unsteady change of influences Artificial weathering testing (DIN 4892-1/2/3): UV-dosage of 60W Water spraying optional Constant conditions www.Q-lab.com Fig. 4 : Setup of a climate chamber. Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 5 5
2. Comparison between natural and artificial weathering 2.2 Impact of weathering on WPC: UV-radiation: Polymer crystallinity Chain scissions Delignification of wood fibers Wet-dry cycling: Fiber swelling Fiber detachment Degradation of interfacial bonding Fig. 5 : Naturally weathered specimen 1 year Frost-thaw cycling: Central Europe Embrittlement of polymer matrix PP-matrix / 70% pine-fibered Surface erosion Brushed surface Reduction of profile`s cross-section Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 6
2. Comparison between natural and artificial weathering 2.3 Research questions arising: 1. How many years of natural weathering correspond to x-days of artificial weathering? 2. How does fibre content affect the durability of WPC? 3. Which formula can be used to calculate the natural durability in years from artificial weathering given in days? 2.3 Study approach: Literature research about artificial and natural weathering of WPCs Clustering data according to fiber content and exposure duration Comparison of empiric data on strength loss under both weather regimes Interpolation of lacking data Derivation of acceleration factors and setup of algorithm model Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 7
3. Computing of WPC ageing 3.1 Results from literature review: wood MOR Duration Reference content loss MOR wood t [hrs.] Duration μ [%] [%] loss content Location Reference t [hrs.] μ [%] Soccalingame et al. [1] 336 10 2.5 [%] Kallakas et al. [2] 500 20 1.8 9.8 5760 30 Brasil / PP Silva et al. [7] 11.8 8640 Sélden et al. [3] 480 25 5.0 0.8 1440 Sélden et al. [3] 960 25 9.0 4.8 2880 Sélden et al. [3] 1344 25 19.0 33 China / PP Zhou et al. [8] 9.8 4320 Soccalingame et al. [1] 336 30 4.2 12.4 8640 Kallakas et al. [2] 500 35 6.5 8.7 2880 Beg and Pickerig [4] 500 40 8.0 9.8 4320 Homkhiew et al. 13.0 45 5760 Thailand / PP Beg and Pickerig [4] 1000 40 13.0 [9] 17.4 7200 Sélden et al. [3] 480 50 12.0 21.7 8640 Sélden et al. [3] 1344 50 20.0 6.0 50 2000 Malaysia / HDPE Taib et al. [10] Stark et al. [5] 1000 50 15.0 18.4 11520 Falk et al. [6] 1500 50 19.5 60 Thaiwan / HDPE Hung et al. [11] 17.4 25920 Stark et al. [5] 2000 50 19.0 Stark et al. [5] 3000 50 47.0 Table 1 : Literature and data on artificial weathering Table 2 : Literature and data on natural weathering Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 8
3. Computing of WPC ageing 3.2 Location of natural weather WPC trials: Most reported trials are around the equator Zhou et al. [8] Taib et al. [1] Homkhiew et al. [9] Hung et al. [11] Silva et al. [7] Fig. 6 : Locations of natural weathering trials reported from scientific literature Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 9
3. Computing of WPC ageing 3.3 Practical Problems : Data is limited to a low number of scenarios on fiber contents and exposure durations MOR- declines (=MOR↓) from artificial weathering not directly comparable to data from natural weathering due to differing fiber contents (=μ) Fig. 7 : MOR↓ -matrix from each compound tested Basic assumptions needed : Ageing is expressed by loss in MOR ↓ MOR ↓ is a linear function of exposure time t and fiber content μ Further approach : Linear inter- and extrapolation of exposure times t artificial or t natural to a common fiber content μ and MOR↓ Basic question : How much longer is exposure time under natural weathering when reaching a similar MOR-decline than under artificial weathering given equal fiber shares Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 10
3. Computing of WPC ageing 3.4 Procedure: Acceleration : Comparison between MOR ↓ nat (12/8) and MOR↓ art (4/3) MOR↓ nat at 8.5MPa loss and μ =45% fiber share 1 Extrapolation to μ =25% leading to MOR ↓* nat at 5.5 MPa loss 2 Increasing exposure time to t* nat until MOR↓* nat equals MOR↓ art 3 and compared with MOR ↓ art tested under μ =25% at t art ⇒ Acceleration Factor = t* nat / t art 3 1 2 3 Fig. 8 : Procedure of data adaption and comparison for derivation of acceleration or deceleration factors between artificially and naturally weathered specimens. Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 11
3. Computing of WPC ageing 3.5 Acceleration and Deceleration Factors: Deceleration-Factors ( α dec )derived Acceleration-Factors ( α acc )derived from 117 single comparisons: from 117 single comparisons: „Smmothed" Mean α dec = 7.7 Mean α acc = 8.1 α acc/dec =7.35 Outlier values Fig. 9 : Acceleration-Factors received from data groups Fig. 10 : Deceleration-Factors Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 12
3. Computing of WPC ageing 3.6 Computed Algorithm for WPC-Durability calculations: Algorithm for calculation of MOR↓ as a function of exposure time and fiber content : MOR↓ [%] = 5.8 • 10 -3 • μ • t nat - 3.5 • 10 -4 • t nat + 16 • μ - 5.0 2880h ≤ t nat ≤ 8640h 0.30 ≤ μ ≤ 0.45 e.g .: h=2880h; μ=0.33 ⇒ MOR ↓= 4.8% (see Table 2). Fig. 11 : Ageing-Topography of WPC showing MOR-decline over exposure time and under various fiber loadings. Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 13
4. Summary Natural weathering degrades WPC strength due to UV-light, humidity and frost-thaw The loss in MOR is a function of exposure time and fiber content Degradation can be assumed as linear progressing within the first 5 years Strength decrease can be elaborated by artificial weathering The received degradation corresponds to a 7.35-times longer period under natural conditions Limitations: The findings belong to climates in equatorial regions For Central European conditions α acceleration is assumed being significantly higher Polymer Testing & Analysis 2019 Session 6: DEVELOPMENTS IN POLYMER PERFORMANCE Daniel Friedrich 14
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