Results

Once the acrylic resins were cured and hardened, simple tests run with a Dynamic Mechanical Analysis (DMA) machine were done.  DMA is a technique where a miniscule force is applied to a small sample of composite. This allows the composite in question to be exposed to stress, temperature, frequency and other values that will be studied.  For a known stress, the sample will deform a certain amount. In DMA this is done sinusoidally and how much the composite bends is related to its stiffness. [3] A force modulus is utilized to generate the sinusoidal wave and this is transmitted to the sample.  The force is equal to the modulus times the displacement of the sample as it slowly heats up.  The graph of the displacement versus the force applied will show a linear change, where the slope of that line is known as E.  The change in the slope at any given point on that line is then graphed and the result is shown below in the Storage Modulus. The Storage Modulus shows the change in stiffness as the small sample heats up. 

The graph starts out with at a very high stiffness for all samples tested, meaning that the samples show very little movement.  Some started off with a higher stiffness than others.  This is because of the amount of Styrene added to the acrylic resin.  The more Styrene - the greater the stiffness.  This being said, each curve shows the same decrease as the sample heated.  This decrease is showing that the samples are becoming more elastic, or rubbery.  At the point that each line changes concavity, from concave down to concave up, the sample loses a great deal of energy and becomes significantly more elastic.  This point is called the Glass Transition Temperature, or Tg.  The Tg of each sample can also be seen in the second graph, below, known as the Loss Modulus.

The Loss Modulus shows how much energy dissipates from the sample as the temperature increases.  The amount of energy released can be seen on the y-axis labeled E".  The reasoning for this is because the Loss Modulus shows the change in the slope of the Storage Modulus over time.  Each of the samples exhibited generally the same initial downward curve, but as the temperature increased, the curves begin to spike upward.  The peak of each curve correlates to the concavity of the Storage Modulus showing that the transition temperature is where the most amount of energy is released.

While the hardened bars were being tested using the DMA machine, small batches of the resin liquid were being tested for viscosity using a machine called an AR2000 rheometer. The AR2000 is a viscometer which can produce a broad spectrum of measurement including linear characterization, creep and relaxation experiments, monitoring of the kinetic for curing reactions or polymer crystallization amongst others.[4]  This machine was able to read the viscosity level for each of the five samples that are shown in the graphs above.  All of the data that was collected from the AR2000 and from the DMA machine can be seen below in Table 2.

Viscosity was measured by Pascals*seconds, Tg was measured in degrees Celsius, E' was measured in Mega Pascals

Once all of the data was collected from both tests, it was noted that the test of 20% Styrene was not mixed properly which lead to inaccurate data.  Because of this, the next best test results were shown by the mixture of 15% Styrene and 15% MFA. This mixture was chosen to be mixed with the glass and cellulose fibers to make a new reinforced composite, as was the 0% Styrene mixture since that was a completely renewable resin mixture.

The fifteen-fifteen mixture was then combined with both the cellulose and glass fibers by using a vacuum to pull the resin though two different twelve sheet thick stacks of those selected fibers.  The same process was used for the zero-thirty mixture, except only one reinforced composite was made out of that mixture using the cellulose fibers.  This would show the effects of a completely renewable composite, as well as two other composites that were almost completely renewable.  Once the composites had hardened in the vacuum overnight and then baked in the oven to remove any Styrene, the three panels were then marked into eight inch by eight inch squares.  After the squares were marked off, the panels were then split up into two sections: one three inch by eight inch section that would be used for presentation, and a five inch by eight inch section that was divided into sixteen 0.5 inch by five inch sections to be used for the testing of the composite.  Pictures of the whole fiber composite making and cutting process can be seen in the Photo Gallery page of this blog, or by simply clicking on Photo Gallery.

When the panels were done getting cut up into sections in the machine shop, the bars were brought back to the lab and put though testing to compare the glass fibers to the cellulose fibers, as well as the completely renewable composite to the fifteen-fifteen composite.  The machine used to do the testing is known as Instron 3382 100kN Universal Test Machine.  This machine uses a three point bending flex fixture to measure the force required to bend a composite under three point loading conditions.  The machine will then give two different sets of data: one that indicates the transverse forces applied to the beam and the corresponding vertical displacements at that force and a second set that reveals the voltage values.[5]