Team:Imperial/Mechanical Testing

From 2014.igem.org

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                         <p><em>“How long would the bacterial cellulose water filter last? What will be the pressure we can apply on to it?”</em>   
                         <p><em>“How long would the bacterial cellulose water filter last? What will be the pressure we can apply on to it?”</em>   
- Dr. Chipps (Principal Research Scientist at Thames Water) </p>
- Dr. Chipps (Principal Research Scientist at Thames Water) </p>
-
                         <p>The most accessible method of finding an answer to Dr. Chipps’ questions is to asses the quality of our material by pulling a test piece until it breaks, a tensile test. The quality of our bacterial cellulose will determine the water pressure that can be applied to it in a membrane bioreactor setting as the filter will be used in a flat orientation. Since the water pressure is the major limiting factor of the flow rates produced in such a setting, a key step to establishing the feasibility of our project is to perform a tensile test. </p>
+
                         <p>The most accessible method of finding an answer to Dr. Chipps’ questions is to asses the quality of our material by pulling a test piece until it breaks, a tensile test. The quality of our bacterial cellulose will determine the water pressure that can be applied to it in when used as a customisable ultrafiltration membrane. Since the water pressure is a major limiting factor of the flow rates produced in such a setting, a key step to establishing the feasibility of our project is to perform a tensile test. </p>
-
                         <p>Tensile testing of bacterial cellulose is a common way of characterising and comparing its mechanical properties (Sherif 2006, Cheng 2009, Shezad 2010) and provides an indication of the orientation of the fibres in the bacterial cellulose pellicle. Therefore, we contacted Dr. Angelo Karunaratne of the <em>Royal British Legion Centre of Blast Injury Studies</em> at Imperial College, requesting access to test samples in an Instron 5866 materials testing machine (Instron Inc., Norwood, USA). Luckily Angelo was welcoming to the idea and allowed us to perform tensile stress-strain tests of our material. The aim was to calculate the young’s modulus, maximum stress applied and strain at failure.</p>
+
                         <p>Tensile testing of bacterial cellulose is a common way of characterising and comparing its mechanical properties (Sherif 2006, Cheng 2009, Shezad 2010) and provides an indication of the orientation of the fibres in the bacterial cellulose pellicle. Another advantage is that for a polycrystalline material like bacterial cellulose grown in static media, the shear stress, directly related to hydrostatic water pressure, can be interpolated based on Von Mises Criterion.</p>
 +
                        <p>Therefore, we contacted Dr. Angelo Karunaratne of the Royal British Legion Centre of Blast Injury Studies at Imperial College, requesting access to test samples in an Instron 5866 materials testing machine (Instron Inc., Norwood, USA). For this test our aim was to calculate the young’s modulus, ultimate tensile stress, yield stress and strain at failure. </p>
                     </section>
                     </section>
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                         <p>Samples were prepared by oven drying at 60°C for 6 hours between VWR 413 filter paper, without pressure. Subsequently, samples were kept at room temperature (20°C) before testing. Cellulose was cut into 0.1 mm x 11 mm x 32 mm dumbbell shapes according to the recommendation from the ISO 527-3 guidelines for determination of tensile properties of plastics. Dumbbell shapes have the advantage of avoiding stress concentration at the clamps, and the dimensions chosen were sufficiently similar to existing literature dimensions, 0.16 mm×100 mm×150 mm to allow for comparison across studies (Sherif 2006). A digital vernier calliper was used to measure the thickness of each of the samples. 8 samples were used for the main cellulose fabric intended for water filtration, fewer were used for alternatively processed samples due to limited availability.</p>
+
                         <p>Samples were prepared by oven drying at 60 C for 6 hours between VWR 413 filter paper, without pressure. Subsequently, samples were kept at room temperature (20 C) before testing. Cellulose was cut into 0.1 mm x 11 mm x 32 mm dumbbell shapes as shown in figure 2 a, following the shape recommended by ISO 527-3 guidelines for determination of tensile properties of plastics. Dumbbell shapes have the advantage of avoiding stress concentration at the clamps, and the dimensions chosen had sufficiently similar small width to large width ratio to literature dimensions (0.16mm × 100mm × 150mm) to allow for comparison across studies (Sherif 2006). A digital vernier calliper was used to measure the thickness of each of the samples. 9 samples were used for the main cellulose fabric intended for water filtration, 2 were used for blended cellulose samples due to limited availability.</p>
                          
                          
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                             <figcaption>Figure 3: Cellulose failing under stress</figcaption>
                             <figcaption>Figure 3: Cellulose failing under stress</figcaption>
                         </figure>
                         </figure>
-
                         <p>The test involves clamping test pieces into the Instron machine, moving the upper clamp upwards at a specific rate, ‘elongation time’, set to 20 mm/min to match that of existing literature (Sherif, 2006) and tracking the tensile force this introduces in the BC sample until the sample breaks, failure. Stress(σ) was calculated as the tensile force divided by the cross sectional area measured as width x thickness. Young’s modulus was calculated as stress/strain. Strain (ε) was calculated as ΔL/L<sub>0</sub>where ΔL is the elongation from the initial length L<sub>0</sub>.Samples were tested until visually confirming failure as shown in figure 3.</p>
+
                         <p>The test involves clamping test pieces into the instron machine, moving the upper clamp upwards at a specific elongation time, set to 20 mm/min to match that of existing literature (Sherif, 2006) and tracking the tensile force of the BC sample until the sample fails. Stress() was calculated as the tensile force divided by the cross sectional area measured as width x thickness. Young’s modulus (E) was calculated as stress/strain in the linear section of the average graph. Strain () was calculated as L/L0where L is the elongation from the initial length L0. Samples were tested until visually confirming failure as shown in figure 3.</p>
                          
                          
                      
                      
-
                             <p>Two main sample types were tested. The BC pellicles intended for water filtration were immersed in a solution of Active Oxygen Fabric Stain Remover dissolved in distilled water. After 4 days, the pellicles were removed from the container, cut into squares of 5 cm by 5 cm, and allowed to dry between VWR 413 filter paper in an oven at 60°C for 3 hours. Then, the BC layered in filter paper was moved to room temperature, folded in Blue Roll, clamped between heatproof mats with mechanical clamps and left for 24 hours. This type of cellulose will be referred to as non-blended BC. </p>
+
                             <p>Two main sample types were tested. The BC pellicles intended for water filtration were immersed in a solution of Wizz Active Oxygen Fabric Stain Remover dissolved in distilled water. After 4 days, the pellicles were removed from the container, cut into squares of 5cm by 5cm, and allowed to dry between VWR 413 filter paper in an oven at 60 ⁰C for 3 hours. Then, the BC layered in filter paper was moved to room temperature, folded in Blue Roll, clamped between heatproof mats with mechanical clamps and left for 24 hours. This type of cellulose will be referred to as non-blended BC. </p>
                             <p>Alternative BC samples were treated in a 0.1 M NaOH solution in 80C for 3 hours, upon which it was dried off with blue roll and immersed in distilled water. After being in the distilled water solution for 12 hours, the BC was dried of with blue roll and blended in a Jamie Oliver food processor for 12 min at speed 2.</p>
                             <p>Alternative BC samples were treated in a 0.1 M NaOH solution in 80C for 3 hours, upon which it was dried off with blue roll and immersed in distilled water. After being in the distilled water solution for 12 hours, the BC was dried of with blue roll and blended in a Jamie Oliver food processor for 12 min at speed 2.</p>
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                             <figcaption>Figure 9: Tensile Stress Average of Blended Cellulose </figcaption>
                             <figcaption>Figure 9: Tensile Stress Average of Blended Cellulose </figcaption>
                         </figure>
                         </figure>
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                         <p>The results of the mechanical tests of blended BC and non-blended BC are shown in table 1. The corresponding measurement data are shown in figure 3 and 4. As shown in table 1, the E, σand ε of non-blended BC was 1.52 MPa, 30 MPa and 35%, respectively. 10 samples were tested to check for variability in the cellulose samples produced as graphed in figure 5. </p>
+
                         <p>The results of the mechanical tests of blended BC and non-blended BC are shown in table 1. The corresponding measurement data are shown in figure 3 and 4. As shown in table 1, the E, and  of non-blended BC was 1.52 MPa, 30 MPa and 35%, respectively. 9 samples were tested to account for variability in cellulose samples produced as graphed in figure 5. The tensile stress is equal within standard deviation to that of 34 MPa  found by (Chen 2009), indicating literature levels of tensile strength of the material produced. </p>
                          
                          
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Revision as of 02:32, 17 October 2014

Imperial iGEM 2014

Aqualose

Mechanical Testing

Overview

To check the feasibility of using our bacterial cellulose as a customisable ultrafiltration membrane, the mechanical properties were tested. For this to work, we checked the tensile strength of our filter, calculated the shear stress and estimated the processing method that produces membrane with the longest life-time. Our ultimate tensile stress calculated matched with literature values of bacterial cellulose within standard deviation, and the data analysis provided the insight to use non-blended cellulose rather than blended..

Key Achievements

  • Introduced a new aspect to the manufacturing track in terms of quantitatively characterising the mechanical properties of our product, bacterial cellulose
  • Quantified the tensile stress-strain properties of our bacterial cellulose.
  • Established the feasibility of using bacterial cellulose as a customisable ultrafiltration membrane with water pressures of 75 bar within a conservative safety margin.
  • Discovered that non-blended compared to blended bacterial cellulose was significantly more ductile, and would have longer life time as water filter, which informed the choice of cellulose for the final product.
  • Tested and analysed 20 samples of bacterial cellulose test pieces.
  • Created a size and quality optimised gif for visualisation of the experiment and written protocol for future iGEM teams to do the same.

Introduction



“How long would the bacterial cellulose water filter last? What will be the pressure we can apply on to it?” - Dr. Chipps (Principal Research Scientist at Thames Water)

The most accessible method of finding an answer to Dr. Chipps’ questions is to asses the quality of our material by pulling a test piece until it breaks, a tensile test. The quality of our bacterial cellulose will determine the water pressure that can be applied to it in when used as a customisable ultrafiltration membrane. Since the water pressure is a major limiting factor of the flow rates produced in such a setting, a key step to establishing the feasibility of our project is to perform a tensile test.

Tensile testing of bacterial cellulose is a common way of characterising and comparing its mechanical properties (Sherif 2006, Cheng 2009, Shezad 2010) and provides an indication of the orientation of the fibres in the bacterial cellulose pellicle. Another advantage is that for a polycrystalline material like bacterial cellulose grown in static media, the shear stress, directly related to hydrostatic water pressure, can be interpolated based on Von Mises Criterion.

Therefore, we contacted Dr. Angelo Karunaratne of the Royal British Legion Centre of Blast Injury Studies at Imperial College, requesting access to test samples in an Instron 5866 materials testing machine (Instron Inc., Norwood, USA). For this test our aim was to calculate the young’s modulus, ultimate tensile stress, yield stress and strain at failure.

Methods

Figure 1: Instron 5866 materials testing machine
Figure 2b: Actual test state: tensile testing state of thin bacterial cellulose pellicle
Figure 2a: Dumbbell shape used as the shape for testing

Samples were prepared by oven drying at 60 C for 6 hours between VWR 413 filter paper, without pressure. Subsequently, samples were kept at room temperature (20 C) before testing. Cellulose was cut into 0.1 mm x 11 mm x 32 mm dumbbell shapes as shown in figure 2 a, following the shape recommended by ISO 527-3 guidelines for determination of tensile properties of plastics. Dumbbell shapes have the advantage of avoiding stress concentration at the clamps, and the dimensions chosen had sufficiently similar small width to large width ratio to literature dimensions (0.16mm × 100mm × 150mm) to allow for comparison across studies (Sherif 2006). A digital vernier calliper was used to measure the thickness of each of the samples. 9 samples were used for the main cellulose fabric intended for water filtration, 2 were used for blended cellulose samples due to limited availability.

Figure 3: Cellulose failing under stress

The test involves clamping test pieces into the instron machine, moving the upper clamp upwards at a specific elongation time, set to 20 mm/min to match that of existing literature (Sherif, 2006) and tracking the tensile force of the BC sample until the sample fails. Stress() was calculated as the tensile force divided by the cross sectional area measured as width x thickness. Young’s modulus (E) was calculated as stress/strain in the linear section of the average graph. Strain () was calculated as L/L0where L is the elongation from the initial length L0. Samples were tested until visually confirming failure as shown in figure 3.

Two main sample types were tested. The BC pellicles intended for water filtration were immersed in a solution of Wizz Active Oxygen Fabric Stain Remover dissolved in distilled water. After 4 days, the pellicles were removed from the container, cut into squares of 5cm by 5cm, and allowed to dry between VWR 413 filter paper in an oven at 60 ⁰C for 3 hours. Then, the BC layered in filter paper was moved to room temperature, folded in Blue Roll, clamped between heatproof mats with mechanical clamps and left for 24 hours. This type of cellulose will be referred to as non-blended BC.

Alternative BC samples were treated in a 0.1 M NaOH solution in 80C for 3 hours, upon which it was dried off with blue roll and immersed in distilled water. After being in the distilled water solution for 12 hours, the BC was dried of with blue roll and blended in a Jamie Oliver food processor for 12 min at speed 2.

Figure 4: Active Oxygen Fabric Stain Remover treated BC for 4 days
Figure 5: a) 0.1 M NaOH treated BC, blended and spread onto VWR 413 filter paper to dry b) Phillips Jamie Oliver Blender that produced the BC of part a.

Results

Figure 6: Tensile Stress-Strain Graph of Bacterial Cellulose
Figure 7: Average Tensile Stress-Strain Graph of Bacterial Cellulose
Figure 8: Tensile Stress-Strain Graph of Blended Bacterial Cellulose
Figure 9: Tensile Stress Average of Blended Cellulose

The results of the mechanical tests of blended BC and non-blended BC are shown in table 1. The corresponding measurement data are shown in figure 3 and 4. As shown in table 1, the E, and of non-blended BC was 1.52 MPa, 30 MPa and 35%, respectively. 9 samples were tested to account for variability in cellulose samples produced as graphed in figure 5. The tensile stress is equal within standard deviation to that of 34 MPa found by (Chen 2009), indicating literature levels of tensile strength of the material produced.

Sample processing Ultimate tensile stress (MPa) Yield stress (Mpa) Young's modulus (Mpa) Strain at break (%)
Non-blended bacterial cellulose 29.9 ± 6.4 25.2 ± 7.2 1.5 ± 0.1 21 ± 3
Blended bacterial cellulose 208 ± 80 155 ± 11 50.5 ± 1 4.1 ± 0.9
Table 1

Discussion

Limitations

Appendix

References

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