Lignin-Polyolefin Blends
Another application of lignin is its use as a blend with polyolefins, and the main objectives of incorporating lignin in polyolefins are to act as a stabilizer against oxidation under UV radiation or at elevated temperatures, or conversely to enable the biodegradation of the material. This type of polymer blending has found good compatibility between hydrophobic lignin and high density polyethylene (HDPE) with little change in properties. However, poor compatibility has been reported with low density polyethylene (LDPE) [75-79]. In these experiments, some improvements in the tensile modulus of low density polyethylene (LDPE) were found with greater than 20 wt% lignin incorporation, but tensile strength was poor. The differences observed between HDPE and LDPE suggest that molecular architecture may play an important role as chemical structure in determining the compatibility of lignin in blends, as the interactions between lignin and the many short branching chains of LDPE may be entropically unfavorable. The ability of lignin-degrading microorganism Phanerochaete chrysospo — rium to attack polyethylene and polypropylene was investigated by Mikulaova and coworkers [78]. In this experiment they used a series of polymer blends containing 10, 20 and 30% lignin obtained from the waste product of the pulp and paper industry. Measurement of the tensile strength after 30 days of degradation showed that the mechanical properties of the polymer blends were decreased during the biodegradation process. The isolation of oligomer fractions
|
Adhesive |
Resin performances |
Plywood performance |
||||
|
Viscosity (mPa s) |
Solid content (%) |
Free formaldehyde (%) |
Free phenol (%) |
Bonding strength (MPa) |
Formaldehyde emission (mg/L) |
|
|
PF |
100 |
48.9 |
0.10 |
0.65 |
1.65 |
0.13 |
|
10% ERPFa |
127 |
45.0 |
0.10 |
0.31 |
1.40 |
0.24 |
|
30% ERPF |
175 |
47.3 |
0.23 |
0.15 |
1.06 |
0.11 |
|
30% ERPFb |
100 |
48.7 |
0.31 |
0.13 |
1.32 |
0.10 |
|
50% ERPF |
235 |
50.0 |
0.32 |
0.24 |
0.98 |
0.23 |
|
50% ERPFb |
160 |
49.5 |
0.47 |
0.26 |
1.31 |
0.11 |
|
70% ERPF |
260 |
46.3 |
0.12 |
0.33 |
0.65 |
0.21 |
|
Table 10.7 Adhesives resins prepared with different substitution ratios of ethanol plant residue lignin (ER) and their performance [71]. |
|
PF — Phenol-formaldehyde resin a 10% ERPF — the phenol-formaldehyde resin adhesive with 10%- phenol is substituted with ER (ethanol plant residue lignin) |
b Adhesives were produced in an adhesive factory and used in actual plywood industry
by tetrahydrofuran (THF) extraction of biodegraded polymers and their characterization by gel permeation chromatography (GPC), UV and Fourier transmission infrared (FTIR) spectroscopy indicated that biotransformation of the lignin component during the exposure to microorganisms initiates a partial biodegradation of the synthetic polymer matrix [78].