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Current Methodologies for Testing Degradability of Agricultural Mulches and Future Approaches

Current Methodologies for Testing Degradability of Agricultural Mulches and Future Approaches. Douglas G. Hayes Dept. Biosystems Engr. and Soil Sci. University of Tennessee Knoxville, TN 37996-4531. SCRI PLANNING MEETING: SPECIALTY CROPS / DEGRADABLE MATERIALS October 30, 2008

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Current Methodologies for Testing Degradability of Agricultural Mulches and Future Approaches

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  1. Current Methodologies for Testing Degradability of Agricultural Mulches and Future Approaches Douglas G. Hayes Dept. Biosystems Engr. and Soil Sci. University of Tennessee Knoxville, TN 37996-4531 SCRI PLANNING MEETING: SPECIALTY CROPS / DEGRADABLE MATERIALS October 30, 2008 University of Wisconsin, River Falls

  2. Goals for Testing • Comparison of material props of mulches • Evidence of degradation • Quantitative data of degradation time course • Comparison of materials, procedures • Comparison to the literature • Understanding of underlying degradation mechanism, relationships between • Physical changes • Chemical changes • Protective performance of mulch / cover

  3. Systems for Testing R.J. Muller, 2003

  4. Quantities to be Measured • Physical • Structural integrity • Mechanical strength • Location of cleavage sites • Chemical • Loss of mass • Change of average molecular weight (MW) • Distribution of MW • Identifying functional groups being cleaved; underlying kinetic mechanism

  5. I. Physical Testing • Color • Light Transmission • Scanning Electron Microscopy, SEM • Differential Scanning Calorimetry, DSC • Glass Transition Temperature, Tg • Melting Point Temperature, Tm • Gel Content • Tensile Strength, Elongation, Strain Energy • Weight  g m-2, thickness • Dynamic Rheology: G’ and G” moduli • Surface Area by ??

  6. Color Change  Darkening • Colorimeter = Simple measurement • Workup: recovery of mulch, removal of excess soil • 3 filters ~response similar to eye, • (Spectrophotometer: amount of light reflected or transmitted at each wavelength) • Color Change Parameter: • DE = [ (L-L0)2 + (a-a0) 2 + (b-b0) 2]0.5 • L = brightness • a = red • b = yellow • Color change may represent • Adsorption of soil • degradation  Yellowing Kijchavengkul et al, 2008

  7. Light Transmission (%T) • Workup = same as for colorimetry • Spectrophotometry, 400-700 nm, Transmission • Depicts changes in openness between fibers • As % T Increases, weed formation is more probable • Decrease of %T with time: soil adsorption? Kijchavengkul et al, 2008

  8. SEM b) SB PLA Control at 500X SEM of 20S3 (Promot MZM + Molasses) at 500X • Qualitative information on soil adsorption, fiber degradation • Wadsworth et al, unpublished, 2008

  9. Differential Scanning Calorimetry (DSC) (ASTM D-3418) • -60oC 160oC @ 10oC/min • Tm peak broadens upon degradation when x-linking occurs • Gel formation: Xg = 1-exp(k Dtn) (Avrami Eq) -Increase of Xg ~ cross-linking (X-ray diffraction can support; Alt: ASTM D-2765) T for transition to amorphous • Tm Kijchavengkul et al, 2008

  10. Tensile Strength (Strength at Breakage), Elongation (under Load at Breakage) and Strain Energy (ASTM D 882) Increase of Brittleness Kijchavengkul et al, 2008 Ho et al. 1999

  11. Tensile Strength (Strength at Breakage), Elongation (under Load at Breakage) and Strain Energy (ASTM D 882) • Samples stored in dessicators at a fixed, common, relative humidity for ~48 hr • Sample swatches should be made both in the direction parallel and perpendicular to extrusion • Breakage ~ physical disintegration into fragments Kijchavengkul et al, 2008 Ho et al. 1999

  12. II. Chemical Testing • Size Exclusion Chromatography (SEC) = Gel Permeation Chromatography (GPC) • FTIR Spectroscopy • NMR Spectroscopy • MALDI-TOF Mass Spectroscopy • Gas Chromatography-Mass Spec (GC/MS) (of residuals in soil or water) • CO2 formation / O2 consumption

  13. GPC Analysis of Ricinoleyl / w-Pentadecanoic acyl Co-Polymers Kelly and Hayes, 2006

  14. GPC • Workup: Dissolve mulch in solvent (CHCl3; Ionic Liquid?) • Dilute w/ mobile phase (THF) • Often, multiple columns linked in series • RI or light scattering detector  (via static LS) Mw • Chromatogram Mn, PDI; area per mass of net Ho et al, 1999

  15. GPC Calibration of Star Polymers Typically, Polystyrene or Polyethylene glycol standards used Kelly and Hayes, 2006

  16. FTIR-Attenuated Total Reflectance (-ATR) • Loss of intensity at 1710 cm-1 (C=O stretching) and 1270 cm-1 (C-O stretching  chain scission of ester group Kijchavengkul et al, 2008

  17. 1H-NMR Kelly and Hayes, 2006 Useful for low-MW oligo’s

  18. MALDI Ricinoleic acid + Pentaerythritol Useful for low-MW oligo’s, co-polymer Kelly and Hayes, 2006

  19. Use of Chemical and Physical Data • Physical and chemical data compared: how are structural disintegration and lowering of MW interrelated? • Phys and chem data compared to performance as a protective agent • Phys and chem data compared to environmental changes in the field (T, sunlight, r.h., etc.)

  20. References • Ho, KL, et al, J Environ Poly Degr 7, 167 & 173 (1999) • Kelly, AR, Hayes, DG, J Appl Poly Sci 101:1646-1656 (2006) • Kijchavengkul, T., et al., Chemosphere 71: 942 & 1607 (2008) • Muller, RJ, in: Biopolymers, Volume 10, General Aspects and Special Appli cations, A. Steinbuchel, ed. Weinheim, Germany: Wiley, 2003.

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