RISE Poster 2017
Undergraduate Category: Engineering and Technology Degree Seeking: B.S. Chemical Engineering and Mathematics Abstract ID# 1498
Selective Positioning of Cellulose Nanocrystals to Form High Performance Discontinuous Fiber Composites. Evan Z. Toth, Jessica L. Faust and Randall M. Erb Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA USA
Motivation Discontinuous fiber composites allow us to disperse stronger particles into semi-crystalline polymers in order to strengthen them. The major drawback in this process is the weak interface between the polymer and the strengthening particle. Minimal interaction between these two components allows for the propagation of micro-cracks as strain on the composite increases. In this study, alumina filler within a polypropylene (PP) matrix is decorated with cellulose nanocrystals (CNCs) to improve the interface. The goal is to develop a cheap and effective way for both constituents to communicate with each other and resist mechanical failure for a longer amount of time.
Goal and Approach
Discontinuous Fiber Composite (DFC)
Fiber Reinforcement
•CNCs and PP were chosen due to the favorable interaction between them that locally nucleates crystallization as well as their relatively low cost
•Discontinuous fiber composites tend to sacrifice toughness for the sake of strength. •When a filler particle is dispersed in a fiber matrix the boundary usually has poor interaction
Methods and Materials
Traditional DFC Under a Load
•The composite may be stronger than the nonreinforced polymer, but micro-cracks can form and propagate from stress concentrations. Micro-crack formation
Micro-crack propagation
Applications High Performance Plastics Increasing both the toughness and strength of the composite creates a more functional material. Integrating both desirable factors allows for a single composite that lasts longer and thus is more economically efficient. Crystalline Region
Semi-crystalline Region
Hybrid Particle
Extracting CNCs
Producing Hybrid Particles
•Alumina added to DI water in a relation of about 50 % w/v (mg/mL) and put in a sonicating •Cotton balls were used as the CNC bath for 30 seconds to break up aggregates. source after some testing •The saturation limit of alumina to CNCs determined to be about 25 mg/mL (Al2O3/CNC) •The cotton was stirred in 60% w/w •The sonicated uncoated platelets were added H2SO4 in water at 60oC to the previously neutralized and sonicated CNC •Hydrolyzed solution was neutralized solution and then vacuum filtered on a 90mm with NaOH and then sonicated 5 times cotton filter •Filter was then dried in an oven at 60oC. The for 2 minutes each with a 1 minute rest period between each sonication. hybrid particles (HPs) were then scraped off of the filter paper into DI water.
Polymer Composites with Stiffness Gradient •About 0.9g of PP was immersed in ~10mL of xylene and stirred in an oil bath for 60 min. at 140oC. •Once system reached 140oC and PP was completely melted, heat was turned off and around 75oC the final solution of HPs was added to the PP-xylene dispersion in a 10% alumina 90% PP weight ratio and quickly taken to the same vacuum filter apparatus as in the previous phase. •The vacuum dried polymer PP-HP composite was then put into a 60oC oven for several days to completely dry •The PP-HP film was then melted into a film at 180oC to ensure uniform dispersion
Results
•Possible to mitigate aforementioned stress concentration by locally crystallizing the polymer matrix around the filler. •Semicrystalline region improves toughness of the composite as well as the strength rather than only strength. Ductile Polymer Matrix Local stiffness gradient
Stiffness gradient improves load transfer and reduces micro-crack formation
Impact •Creates an inexpensive method of strengthening materials that is easily integrated into pre-existing processes. •The new method will allow for a composite that does not sacrifice the toughness in order to improve strength, but rather improves both •If the process proves to be scalable, the new hybrid particles can replace alumina or other ceramics in industrial processes since the overall process of integrating the hybrid particle and polymer is not much different than with a regular ceramic.
Poorly Coated/Bare Alumina
Evenly Coated HP
Future steps •Currently running differential scanning calorimetry (DSC) tests to examine crystallization differences between PP, PPHP, and PP-alumina melts •Polarized light microscopy (PLM) at platelet-polymer boundary in PP-HP to examine stiffness gradient •Further down the line will run mechanical tests on the three types of films to compare physical property data
Clearer view of CNC adsorption
Conclusion As shown by the literature [1], cellulose can be hydrolyzed with sulfuric acid and used as a nucleating agent for polypropylene. However, in this experiment the cellulose-acid solution was neutralized directly with NaOH in order to dually remove the sulfate groups from the cellulose crystals and bring the pH of solution back to neutral. The optimal hydrolysis conditions were determined to be 60% w/w H2SO4 in water stirring for about 60 minutes at 60oC, followed by neutralization and sonication. The next tests dealt with finding the saturation limit of CNCs on alumina platelets, which is about 25 mg alumina to every mL of sonicated CNC solution. Using CNCs for PP nucleation on alumina platelets came from the concepts presented in [1] and [2], and thus far has proven to be viable. The preliminary tests have shown that CNCs behave in the same way as carbon nanotubes (CNTs) on alumina platelets and should nucleate crystallization in the same way as CNTs.
Contact Information:
Evan Toth, [email protected] or Prof. Randall M. Erb, [email protected] 306 Dana Research Center, 360 Huntington Avenue, Boston, MA 02115, USA
References: [1] D. G. Gray, Cellulose, 15, 297-301, 2008. [2] S. Zhang et al., Polymer, 49, 1356-1364, 2008.
Selective Positioning of Cellulose Nanocrystals to Form High Performance Discontinuous Fiber Composites. Evan Z. Toth, Jessica L. Faust and Randall M. Erb Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA USA
Motivation Discontinuous fiber composites allow us to disperse stronger particles into semi-crystalline polymers in order to strengthen them. The major drawback in this process is the weak interface between the polymer and the strengthening particle. Minimal interaction between these two components allows for the propagation of micro-cracks as strain on the composite increases. In this study, alumina filler within a polypropylene (PP) matrix is decorated with cellulose nanocrystals (CNCs) to improve the interface. The goal is to develop a cheap and effective way for both constituents to communicate with each other and resist mechanical failure for a longer amount of time.
Goal and Approach
Discontinuous Fiber Composite (DFC)
Fiber Reinforcement
•CNCs and PP were chosen due to the favorable interaction between them that locally nucleates crystallization as well as their relatively low cost
•Discontinuous fiber composites tend to sacrifice toughness for the sake of strength. •When a filler particle is dispersed in a fiber matrix the boundary usually has poor interaction
Methods and Materials
Traditional DFC Under a Load
•The composite may be stronger than the nonreinforced polymer, but micro-cracks can form and propagate from stress concentrations. Micro-crack formation
Micro-crack propagation
Applications High Performance Plastics Increasing both the toughness and strength of the composite creates a more functional material. Integrating both desirable factors allows for a single composite that lasts longer and thus is more economically efficient. Crystalline Region
Semi-crystalline Region
Hybrid Particle
Extracting CNCs
Producing Hybrid Particles
•Alumina added to DI water in a relation of about 50 % w/v (mg/mL) and put in a sonicating •Cotton balls were used as the CNC bath for 30 seconds to break up aggregates. source after some testing •The saturation limit of alumina to CNCs determined to be about 25 mg/mL (Al2O3/CNC) •The cotton was stirred in 60% w/w •The sonicated uncoated platelets were added H2SO4 in water at 60oC to the previously neutralized and sonicated CNC •Hydrolyzed solution was neutralized solution and then vacuum filtered on a 90mm with NaOH and then sonicated 5 times cotton filter •Filter was then dried in an oven at 60oC. The for 2 minutes each with a 1 minute rest period between each sonication. hybrid particles (HPs) were then scraped off of the filter paper into DI water.
Polymer Composites with Stiffness Gradient •About 0.9g of PP was immersed in ~10mL of xylene and stirred in an oil bath for 60 min. at 140oC. •Once system reached 140oC and PP was completely melted, heat was turned off and around 75oC the final solution of HPs was added to the PP-xylene dispersion in a 10% alumina 90% PP weight ratio and quickly taken to the same vacuum filter apparatus as in the previous phase. •The vacuum dried polymer PP-HP composite was then put into a 60oC oven for several days to completely dry •The PP-HP film was then melted into a film at 180oC to ensure uniform dispersion
Results
•Possible to mitigate aforementioned stress concentration by locally crystallizing the polymer matrix around the filler. •Semicrystalline region improves toughness of the composite as well as the strength rather than only strength. Ductile Polymer Matrix Local stiffness gradient
Stiffness gradient improves load transfer and reduces micro-crack formation
Impact •Creates an inexpensive method of strengthening materials that is easily integrated into pre-existing processes. •The new method will allow for a composite that does not sacrifice the toughness in order to improve strength, but rather improves both •If the process proves to be scalable, the new hybrid particles can replace alumina or other ceramics in industrial processes since the overall process of integrating the hybrid particle and polymer is not much different than with a regular ceramic.
Poorly Coated/Bare Alumina
Evenly Coated HP
Future steps •Currently running differential scanning calorimetry (DSC) tests to examine crystallization differences between PP, PPHP, and PP-alumina melts •Polarized light microscopy (PLM) at platelet-polymer boundary in PP-HP to examine stiffness gradient •Further down the line will run mechanical tests on the three types of films to compare physical property data
Clearer view of CNC adsorption
Conclusion As shown by the literature [1], cellulose can be hydrolyzed with sulfuric acid and used as a nucleating agent for polypropylene. However, in this experiment the cellulose-acid solution was neutralized directly with NaOH in order to dually remove the sulfate groups from the cellulose crystals and bring the pH of solution back to neutral. The optimal hydrolysis conditions were determined to be 60% w/w H2SO4 in water stirring for about 60 minutes at 60oC, followed by neutralization and sonication. The next tests dealt with finding the saturation limit of CNCs on alumina platelets, which is about 25 mg alumina to every mL of sonicated CNC solution. Using CNCs for PP nucleation on alumina platelets came from the concepts presented in [1] and [2], and thus far has proven to be viable. The preliminary tests have shown that CNCs behave in the same way as carbon nanotubes (CNTs) on alumina platelets and should nucleate crystallization in the same way as CNTs.
Contact Information:
Evan Toth, [email protected] or Prof. Randall M. Erb, [email protected] 306 Dana Research Center, 360 Huntington Avenue, Boston, MA 02115, USA
References: [1] D. G. Gray, Cellulose, 15, 297-301, 2008. [2] S. Zhang et al., Polymer, 49, 1356-1364, 2008.
