Table 13.1 summarizes the various treatments conducted in this research project. DDGS were modified by direct treatment with acetic anhydride and maleic anhy­dride solutions. Acetic anhydride and maleic anhydride were obtained from Sigma — Aldrich Chemical Company, St. Louis, MO and used as supplied without further purification. STDDGS and STPW particles were vacuum-oven dried for 24 hr at 80°C. Four hundred grams of filler were boiled in a stirred jacketed reaction ves­sel fitted with a distillation trap at 90°C containing 6 M acetic anhydride/acetone mixture for 24 hrs. In addition, a 5 M acetic anhydride /1 M maleic anhydride/ acetone reaction mixture was also employed. Following incubation, filler materials were filtered, washed three times with acetone, and vacuum-oven dried for 48 hr at 80°C. Hereafter, STDDGS and STPW treated with acetic anhydride (A) or acetic anhydride/maleic anhydride (AM) mixtures will be designated as STDDGS/A and STDDGS/AM, respectively. Weight percentage gains were calculated for the A and AM mixtures to be ~11 and ~12%, respectively.

TABLE 13.1 Weight Percentages in Test Formulations

Composition HDPE MAPE DDGS STDDGS PINEW PW STPW Modifiers

HDPE 100 — — — — — — —

HDPE-MAPE 95 5 — — — — —

To investigate the influence of mixing different fillers to produce an improved composite, STDDGS was mixed with PINEW at various concentrations with and without presence of a 5% maleic anhydride coupling agent (MAPE) (Table 13.1).

The influence of the presence or absence maleic anhydride coupling agent on the physical properties of HDPE-fiUer blends was also investigated (Table 13.1).

Composite blends were extruded with a 27 mm corotating intermeshing twin — screw extruder, with a length/diameter ratio of 40 (Model ZSE-27 American Leis — tritz Extruder Corporation, Branchburg, NJ). The barrel had ten different zones, each 90 mm long, which were controlled at the following temperatures (oC): 100, 160, 170, 190, 200, 200, 210, 210, 205, and 205, respectively. The cord die temperature was set at 200°C. Premixed fillers and HDPE were dry blended in 1 gallon-resalable plastic bags. Materials were then transferred into a single drive feeder (Flex-Tuff Model 306, Schenck/AccuRate, Whitewater, WI) and fed into the extrusion feeder at the rate of 100 g/min. Extruder screw speed was set at 100 rpm. Extruded strands were cooled by immersion in a water bath and then pelletized with a strand pellet­izer (Model 60E, Automatick Plastics Machinery GMbH, Grossotheim, Germany).

Molding was conducted with a 30-ton molding machine (Engel ES 30, Engel Machinery Inc., York, PA) with set point temperatures (°C) for the four zone injec­tion molding barrel set at: feed = 160; compression = 166; metering = 177, and nozzle = 191. The mold temperature was 37 °C. An ASTM test specimen mold was used that included cavities for a ASTM D790 flexural tensile bar (12.7 mm W x 127 mm L x 3.2 mm thickness) and an ASTM D638 Type I tensile bar (19 mm W grip area x 12.7 mm neck x 165 mm L x 3.2 mm thickness X 50 mm gage L). Impact specimen bars were obtained by cutting the flexural specimens in half to 12.7 mm W x 64 mm L x 3.2 mm thickness and notched. The Type I bars were used for the tensile strength property tests. The flexural bars were used to evaluate flexural prop­erties and also used to make impact strength measurements. The Type I bars were used to evaluate changes due to prolonged exposure to water: weight change, color change, and changes in tensile mechanical properties of the composites.