Film Extrusion of Crambe abyssinica/Wheat Gluten Blends

The overall goal of this procedure is to develop a valuable side-stream production method for crambe meal by combining it with wheat gluten and using the extrusion method to produce a bioplastic with enhanced mechanical properties. This method can help answering key questions in the bioplastic field, such as if two minimally processed side streams can be combined into useful plastic material. The main advantage of this technique is that the addition of gluten to the crambe meal results in an extrudate with good cohesion before and after pressing.

The idea is to make a new bio-based plastic material, readily extrudable, that can compete with oil-based plastics. Visual demonstration of this method is critical as the material, preparation, and extrusion steps are all based on know-how and experience, however, improvement is all about methodological development of the process. To begin, obtain crambe seeds, extract the oil, and save the resulting crambe meal.

Next, sieve the crambe meal with a round, fine-mesh stainless steel kitchen sieve to remove the large fiber fractions and uncrushed seeds. Store the sieved meal at minus 18 degrees Celsius to prevent the material from aging. Mill 250 grams of the crambe meal at a time by placing it into a seven liter jar along with 215 25-millimeter-diameter ceramic balls.

Set the revolution rate on the milling machine to 53 rpm, and mill the meal for 24 hours. Before further processing, place the ball-milled crambe meal and wheat gluten powder into open jars, and condition them in a climate-controlled chamber for a minimum of 48 hours at 23 degrees Celsius and a relative humidity of 50%Next, use a mortar and pestle to grind the urea powder into fine particles. Then, heat the glycerol to 65 degrees Celsius in a glass flask, using a temperature-controlled oil bath, and stir with a magnetic stirrer.

Slowly add 15 grams of the urea powder to 25.5 grams of glycerol for every 100 grams of the final mixture, and stir with a magnetic stirrer at 65 degrees Celsius until the urea powder has completely dissolved. Next, use a kitchen mixer to blend the crambe meal and wheat gluten powders at a 60 to 40 weight ratio for five minutes. Then, slowly add 202.5 grams of the glycerol/urea mixture to 297.5 grams of the crambe/wheat gluten blend for every 500 grams of the final mixture.

Combine the two components in a kitchen mixer while stirring for approximately two minutes, until a homogeneous dough is obtained. Set up a twin-screw extruder by setting zones one through 10 along the extruder barrel at a low-temperature profile to prevent the wheat gluten from crosslinking in the barrel. Then, attach a flat sheet die to extrude the films.

Next, choose a screw speed between 30 and 200 rpm to achieve a die pressure between 30 and 40 bar. Feed the dough manually through the hopper with the help of a wooden pusher to support the material flow towards the screws. Set a conveyor belt to operate at 2.0 meters per minute, and use it to pick up the film as it comes out of the die.

Place fans along the belt to cool the film. Run different die temperatures and temperature profiles to select the conditions that give the smoothest film with a minimum number of voids. After extrusion, store the resulting films in a sealed polyethylene bag until further processing or analysis in order to prevent aging and atmospheric water absorption.

Start by cutting 4.4 centimeter squares from the extruded films. Place a sheet of polyethylene terephthalate onto an aluminum plate, and then set the two square pieces of the film on top of the polymer. Then, place a second sheet of polymer on top of the squares, and sandwich it with an aluminum plate on top.

Place the setup into a press, and adjust the pressure gauge to 50, 75, or 100 bar. Then, press the films for five to 10 minutes while heating the plates to 110, 120, or 130 degrees Celsius. The most critical step for film preparation is the extrusion.

The samples of varying crambe content, which were analyzed here, were extruded using a low-temperature profile with an initial die temperature of 125 degrees Celsius and a zone 11 temperature of 115 degrees Celsius. The maximum stress and strain at the maximum stress are shown here, as a function of crambe content in the crambe/wheat gluten mixture. The maximum stress was found to be highest at 60%crambe content, which was also mirrored in the strain at the maximum stress.

While attempting this procedure, it's important to remember that biological materials taken directly from nature are commonly not suitable for high-temperature treatment. The challenge is to find a process that gives good cohesion without overheating. We found these methods to give a material with promising properties.