MANUFACTURING OF POLYPROPYLENE COMPOSITES WITH IMPROVED TOUGHNESS USING NANOCELLULOSE

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: ACTIVE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1023887
• Project Start Date: Jul 24, 2020
• Project End Date: Jul 15, 2025
• Program Code: [(N/A)]- (N/A)

Recipient Organization
AUBURN UNIVERSITY
108 M. WHITE SMITH HALL
AUBURN,AL 36849

Performing Department
School of Forestry

Non Technical Summary
The overall goal of this project is to develop nanocellulose materials reinforced polypropylene composites and their manufacturing process for potential commercial applications in construction, automotive, and packaging. Nanocellulose is a cellulose fiber with one dimension in less than 100 nanometers and it can be isolated from cellulose structures naturally occurring in wood cell walls. It is an abundant, stiff, strong, and lightweight material. With the size decreasing from bulk wood cells to the nanometer scale format, the stiffness (elastic modulus) of cellulose fiber increases from around 10 GPa to 145 GPa, thus it is ideal for utilization in structural materials or value-added products. Especially, there is significant potential to use nanocellulose in reinforced polymer composites with improved toughness and fracture resistance. Industrial manufacturing processes on a lab scale will be adopted to manufacture composite samples for property evaluation. A critical outcome of this work will be the relationship of the manufacturing process, composite structure, and mechanical property of the nanocellulose reinforced polymer composites. A detailed examination of the toughening mechanism of nanocellulose in polymers will be provided. The knowledge developed in this project will deliver a new category of tough nanocellulose polymer composites with applications in areas such as construction materials, automotive parts, and packaging products. The composite materials that will be developed in this project meet the demand of sustainability of associated industries in construction, automotive, and packaging. Simultaneously, the high-performance nanocellulose polymer composite materials have the potential to move forest products into high value-added applications and completely new markets.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
123	0650	2020	100%

Knowledge Area
123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0650 - Wood and wood products;

Field Of Science
2020 - Engineering;

Keywords

nanocellulose

polymer composite

toughness

Goals / Objectives
The overall goal of this proposed study is to understand the commercial application potential of the dried nanocellulose in polypropylene using melt processing.1. Development of nanocellulose polypropylene (PP) composites with different loading levels of nanocellulose particles.2. Optimization of the continuous melt process for manufacturing nanocellulose PP composites.3. Research of the effect of nanocellulose on fracture toughness of PP composites under different loading levels.

Project Methods
Development of nanocellulose PP composites will be performed in two steps, adopting the masterbatch concept from plastic packaging industries. Step one is to develop a nanocellulose carrier composite masterbatch which is a concentrated mixture of nanocellulose encapsulated during a melt process into a carrier resin and is then cooled and cut into pellets. The masterbatch is then mixed with the polymer matrix with an appropriate ratio to achieve the final loading level of nanocellulose in polymer composites. The carrier resin for manufacturing the masterbatch is normally the same resin as the polymer matrix. In the masterbatch mixing process, a twin-screw extruder is generally used. Mixing the masterbatch into the polymer matrix is commonly done through a single-screw extruder. This is the standard manufacturing procedure in plastic packaging industries when colored packaging products are manufactured using a color masterbatch. As masterbatches are already premixed compositions, their use alleviates the issues with nanocellulose agglomeration or insufficient dispersion in polymer matrix. The concentration of nanocellulose in themasterbatchis much higher than in the end-use polymer, but nanocellulose particles are already properly dispersed in the masterbatch host resin. The other benefit of using masterbatch allows the processor to mixing functional fillers, nanocellulose in this case, with raw polymer matrix economically during the composites manufacturing process.In this proposal, two different types of nanocellulose will be used in manufacturing PP composites: (1) spray-dried nanofibrillated cellulose (NFC) and spray-dried cellulose nanocrystal (CNC). NFC is obtained by processing dilute slurries of cellulose fibers through grinding or high-pressure homogenizing action and the production of CNC involves the digestion of amorphous cellulosic domains by an acid hydrolysis process. After production, needle and long fibril shape materials exist in NFC suspension and pure smaller size needle shape materials occur in CNC suspension. Spray-drying process formed NFC and CNC into particles with different morphologies and the effect of different morphologies of nanocellulose in reinforcing PP composites will be investigated in this study.A nanocellulose PP masterbatch with 30 wt.% of nanocellulose particles was generated using a C. W. Brabender Prep Mixer. The initial goal of the proposed research here is to maximize the loading of nanocellulose particles in the masterbatch. The masterbatch manufacturing process is directly related to melt flow index of PP. A higher melt flow index PP which has a lower viscosity at the melting temperature will be used. A compatibilizer of maleic anhydride grafted polypropylene (MAPP) in pellets will be added in the process to help disperse nanocellulose particles. MAPP as a compatibilizer can improve mechanical properties significantly on cellulose based polymer composites. The laboratory mixing of nanocellulose particles, MAPP pellets, and PP pellets will be conducted using a C. W. Brabender Prep Mixer. The operation of the mixer is to simulate the functionality of a twin-screw extruder and the benefit using the mixer is the flexibility of studying the extrusion processing parameters, such as temperature, residence time, and mixing screw rotation speed. After mixing, the bulk chunk of masterbatch materials will be ground into granular format which will be easily dry blended with fresh polymer pellets for composite manufacturing.The nanocellulose PP composites will be manufactured by diluting the nanocellulose PP masterbatch to the final loadings of nanocellulose using virgin PP pellets. The final nanocellulose loading will be 6, 10, 15, and 20 wt.%. To minimize the composition variation in masterbatch production, one formulation of masterbatch with fixed weight ratio of PP, nanocellulose and MAPP will be used. The weight ratio of nanocellulose to MAPP will be fixed at 3:1 in the final composite formula. The ground masterbatch pellets will be dry-mixed with PP pellets and the pellet mixture will be extruded in a single-screw extruder to produce composites. The composite extrudate will be solidified directly in an air-cooling system and then be pelletized. The pellets obtained will then be injection molded into shapes specified by ASTM standards.Mechanical properties of the composites, including tensile, flexure, and impact will be tested according to the specific ASTM Standards, including ASTM D638, D790 and D256. The tensile modulus, tensile strength, percent elongation at yield and break, flexural modulus, flexural strength, and impact strength for the composites will be reported. Thermal properties of the composites will be characterized by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The effect of nanocellulose on PP crystallinity will be checked by differential scanning calorimetry (DSC). The fracture surfaces of mechanically tested samples will be characterized by SEM. High resolution images from SEM will be used to examine the fracture mechanism of composites with different loadings of nanocellulose. Furthermore, the relationship among nanocellulose loading level, composite fracture surface morphology, dispersion and distribution of nanocellulose particles in composites, and composite mechanical properties, especially the impact strength, will be determined. The appropriate nanocellulose loadings which have the greatest mechanical performance will be recommended for the next step study and commercial applications.Nanocellulose PP composite with appropriate loading of nanocellulose will be manufactured using different processing temperatures, screw speeds, and residence time. This study will focus on the processes of masterbatch manufacturing, single-screw extrusion, and injection molding. Mechanical properties, color variation, fracture surface morphologies, and thermal properties of composites processed at different parameters will be characterized. The best performance composites will be identified, and the processing window, including temperature, screw speed, and residence time ranges, will be reported.The mechanism of using nanocellulose to improve the toughness of PP composites will evaluated through characterizing the fracture toughness of the composite samples. The effect of different loadings of nanocellulose and MAPP on the fracture toughness will be researched.Effort will be made to communicate with stakeholders coming from forest products, construction, automotive, and packaging industries firstly during our on-going research. This will give us opportunity to interact with the potential industrial partners. The purpose of conversation is to gain feedback at each critical stage of the research such that the outcome could be practical for products development needs from the perspective of stakeholders. The initial primary stakeholders will be from automakers (Ford, Hyundai, etc.) and consumer packaged goods (CPG) brand owner (Procter & Gamble, The Coca-Cola Company, etc.) who currently use polymer-based composites in their systems. The sustainability claim of using renewable resources of nanocellulose will help them to achieve their corporate goal regarding establishing sustainable society. The other effort will be sharing our research findings about manufacturing nanocellulose polypropylene composites within a broader polymer composite research community. Specifically, the research conducted at Auburn University will be presented in annual Automotive TPO Engineered Polyolefins Global Conference held by the society of plastic engineering. This conference is the world's leading forum on the use of rigid and elastomeric thermoplastic polyolefins (TPOs) in automotive and ground transportation. Feedback from these stakeholders and research communities will be evaluated.

Progress 10/01/20 to 09/30/21

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?An MS graduate student has been identified and will start in January 2022 to continue this research. In the next step, we will focus on developing nanocellulose PP composites using the procedures developed in this reporting period. Different loading levels of nanocellulose will be included in PP to investigate the impact of nanocellulose particles on the mechanical behaviors of the produced composites.A concept of masterbatch will be adapted to manufacture the composites. Nanocellulose particles will be thermally compounded with PP at a high loading level and the produced mixture is designated as a masterbatch of nanocellulose in PP. Then the masterbatch will be diluted by PP to form the final formulation of the composites. The masterbatch concept is to help the dispersion and distribution of nanocellulose particles in the final composites, improving the mechanical behaviors. The masterbatch of nanocellulose in PP with the highest loading level of nanocellulose particles will be identified. The processing parameters of manufacturing nanocellulose PP masterbatch, including mixing temperature, mixing blade rotation speed, and mixing time,will be optimized.The final composite mechanical and rheological properties will be characterized. The effect of processing parameters and nanocellulose loading levels on mechanical behaviors of the final composites will be reported.

Impacts
What was accomplished under these goals? During this project period, we procured materials for this research, including cellulose nanocrystal(CNC) particles (CelluForce NCV100), homopolymer polypropylene (PP) pellets ExxonMobilTM PP1264E1, and a coupling agent maleic anhydride grafted PP (MAPP) polybondTM3200. A laboratory capable of manufacturing and characterizing nanocellulose PP composites was established. The capability of measuring the mechanical properties of polymer composites reinforced by nanocellulose according to ASTM standards D638, D790, and D256 was also established. Virgin PP pellets need to go through a mixing process for manufacturing nanocellulose PP composites. The first objective was to investigate if the mixing process significantly impacts the mechanical properties of pure PP. In this initial study, PP pellets were processed through a batch mixer at 200°C. For each batch PP processing, 200 grams of pellets were added into the mixing chamber of a C.W. Brabender internal mixer (CWB-2128, Hackensack, NJ) with the two mixing bowls rotating counterclockwise at 60 rpm. After PP melting, the pellets were mixed for another 5 minutes simulating the mixing process when nanocellulose PP composites are manufactured. After mixing, the melt was cooled down to room temperature followed by grinding into pellets around 3 mm using a granulator. Then the pellets after grinding were used to manufacture mechanical testing specimens according to ASTM Standards D638, D790, and D256 using a laboratory injection molder. Differentinjection molding temperatures were tried at 180, 190, 200, and 210°C. A final temperature of 200 °C was determined to be used in the injection molding process. The same injection molding pressure was used during the specimenpreparation processes. The mechanical properties, including tensile, flexural, and impact, for thermally processed PP were measured. Virgin PP pellets without thermal compounding were used to manufacture control samples through the injection molding process directly. Statistical analysis was performed to compare the mechanical properties of the PP specimens produced from virgin and thermally processed pellets. The tensile modulus of PP after thermal processing is significantly greater than that of virgin PP without thermal processing while the tensile strength and the percentage elongation at yield did not change significantly. The tensile modulus increased from 1473 MPa for PP without thermal treatment to 1578 MPa with thermal processing, a 7% increase. The flexural property of PP changed significantly after the thermal treatment. The flexural specimens did not yield or break at 5% strain during the standard tests and the flexural stress at 5% was reported in this study. Both flexural modulus and stress at 5% strain increased significantly after thermal processing, from 1438 MPa and 46.6 MPa to 1679 MPa and 52.5 MPa, respectively. Both notched and unnotched impact strength of PP was tested. The notched impact strength of PP after thermal treatment decreased significantly from 1.84 to 1.62 kJ/m2. The unnotched impact strength before and after thermal treatment is not significantly different. The notched impact strength of PP is sensitive to the thermal treatment during composite manufacturing. In conclusion, thermal treatment of PP virgin pellets significantly changed their mechanical properties using the procedures in this study. The PP specimens used as control samples should be prepared using the same processes which will be used for manufacturing nanocellulose PP composites.

Publications

• Type: Journal Articles Status: Other Year Published: 2021 Citation: Peng, Y.; Via, B. The effect of cellulose nanocrystal suspension treatment on suspension viscosity and casted film property. Polymers 2021, 13, 2168. https://doi.org/10.3390/polym13132168
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Peng, Y.; Xia, C.; Via, B. Characterization of cellulose nanocrystal suspension rheological properties using a rotational viscometer. Forest Products Journal 2021, 71(3): 290-297.

Progress 07/24/20 to 09/30/20

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We will focus on establishing a research laboratory having the capability toconduct the research of manufacturing and characterization ofnanocellulose polypropylene (PP) composites. The initial plan needs the laboratory to be equipped with a batch mixer mixing different additives with molten polymers. Then a grinder will be used to downsize the solidified mixture into pellets with the size of 3-5 mm. Following grindingan injection molder will be used to manufacture the specified specimens from the pellets for propertycharacterizations. A MS graduate student will be recruited in 2021 to performthe research of manufacturing nanocellulose PPcomposites. Nanocellulose in dry form will be mixed with PP using the designed loading levels at a temperature above themelting point of PP (around 200 ºC). After solidification, the mixture will be ground into a pellet form using a plastic grinder. The composite specimens will then be manufactured using a laboratoryinjection molding machine. The mechanical behaviors, including tensile, flexural, and impact properties, of the composites will be testedusing auniversal testing machine and an impact tester according to the ASTM standards D638, D790, and D256. The effect of loading level of nanocellulose on the mechanical properties of the composites will be evaluated.The dispersion of nanocellulose in PP will be characterized using a scanning electron microscope.

Impacts
What was accomplished under these goals? During this project period, we did the initial literature research on manufacturing nanocellulose polypropylene (PP) composites and designed the experiments for manufacturing the composites in the laboratory. The references showed that maximum loading level of 30 wt.% nanocellulose in PP could be produced using a batch mixer. At the loading level of 6 wt.%, nanocellulose was observed to increase the impact strength of PP significantly by 23%. An experimental design with the nanocellulose loading levels of6, 10, 15, and 20 wt.% was determinedfor this study. The effect of composite manufacturing process and the nanocellulose loading level on the impact property of PP will be the focus of this study. The impact property enhancement mechanism of PP will be studied in detail. Commercially availablecellulose nanocrystal (CNC) particles in the size range of 1 - 50µm (CelluFOrce NCV100) which was produced by spray-drying of CNC suspensionwill be used in this study initially. The cellulose nanofibril (CNF) in dry form is not available currently. Injection molding grade of PP from ExxonMobil with the grade name of PP1074KNE1 was identified as the matrix polymer in this study. Spray-dried CNC particles and PP pellets were collected from the vendors and are ready for the next step study.

Publications