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 SCRI PLANNING MEETING: SPECIALTY CROPS / DEGRADABLE MATERIALS October 30, 2008 University of Wisconsin, River Falls

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

Systems for Testing R.J. Muller, 2003

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

I. Physical Testing 1.Color 2.Light Transmission 3.Scanning Electron Microscopy, SEM 4.Differential Scanning Calorimetry, DSC a.Glass Transition Temperature, T g b.Melting Point Temperature, T m c.Gel Content 5.Tensile Strength, Elongation, Strain Energy 6.Weight  g m -2, thickness 7.Dynamic Rheology: G’ and G” moduli 8.Surface Area by ??

Color Change 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:  E = [ (L-L 0 ) 2 + (a-a 0 ) 2 + (b-b 0 ) 2 ] 0.5 L = brightness a = red b = yellow Color change may represent Adsorption of soil degradation  Darkening  Yellowing Kijchavengkul et al, 2008

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

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at 500X b) SB PLA Control at 500X Qualitative information on soil adsorption, fiber degradation Wadsworth et al, unpublished, 2008

Differential Scanning Calorimetry (DSC) (ASTM D-3418) Kijchavengkul et al, o C  160 o 10 o C/min T m peak broadens upon degradation when x- linking occurs Gel formation: X g = 1- exp(k  t n ) (Avrami Eq) -  Increase of X g ~ cross- linking (X-ray diffraction can support; Alt: ASTM D- 2765) TmTm T for transition to amorphous

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

Tensile Strength (Strength at Breakage), Elongation (under Load at Breakage) and Strain Energy (ASTM D 882) Ho et al Kijchavengkul et al, 2008 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

II. Chemical Testing 1.Size Exclusion Chromatography (SEC) = Gel Permeation Chromatography (GPC) 2.FTIR Spectroscopy 3.NMR Spectroscopy 4.MALDI-TOF Mass Spectroscopy 5.Gas Chromatography-Mass Spec (GC/MS) (of residuals in soil or water) 6.CO 2 formation / O 2 consumption

GPC Analysis of Ricinoleyl /  - Pentadecanoic acyl Co-Polymers Kelly and Hayes, 2006

GPC Ho et al, 1999 Workup: Dissolve mulch in solvent (CHCl 3 ; Ionic Liquid?) Dilute w/ mobile phase (THF) Often, multiple columns linked in series RI or light scattering detector  (via static LS) M w Chromatogram  M n, PDI; area per mass of net

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

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

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

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

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.)

References Ho, KL, et al, J Environ Poly Degr 7, 167 & 173 (1999) Kelly, AR, Hayes, DG, J Appl Poly Sci 101: (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.