Recipient Organization
UNIVERSITY OF MAINE
(N/A)
ORONO,ME 04469
Performing Department
School of Forest Resources
Non Technical Summary
Forest-based cellulose is among the most abundant renewable polymer resources on earth, and constitutes Maine's largest natural resource. Cellulose derived polymer nanocomposite materials from Maine's forests are extremely promising materials that can provide the next generation of lightweight, renewable materials for a variety of applications including construction, automotive, defense, consumer products, and coatings.There is considerable interest in the automotive industry towards light-weighting vehicles through the application of new material technologies, and polymer matrix composites are of primary importance in meeting the goals of light-weighting. In addition, the application of renewable materials like wood and plant fibers is of interest in meeting sustainability goals and replacement of petroleum-derived feedstocks. The concept of utilizing hybrid or mixed fillers in polymer matrix composites has been explored in the research arena for several decades. Combinations of fillers can provide enhanced material property performance in polymer matrix composites. For example, filler combinations might be chosen to provide improved mechanical properties and reduced water permeability or enhanced electrical conductivity and lighter weight, etc. Addition of fillers can also typically reduce the cost of the resulting composite especially with the application of nature-derived fillers such as cellulose or clay. The proposed research will be of interest to other scientists involved in cellulose nanocomposites research as well as companies that produce and/or use composite materials.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
The overall goal of the proposed work is to explore the feasibility of producing novel hybrid composites made containing combinations of cellulose nanofibrils (CNF) and fiber glass in thermoplastic resins such as polypropylene (PP), thermoplastic polyolefins (TPO), and polylactic acid (PLA) for consumer applications.The specific objectives are:Estimate the material properties of the hybrid composites and compare with polymer matrix composites currently used in industry.Examine various composite manufacturing processes including extrusion, injection molding, and additive manufacturing to manufacture hybrid composite materials.Characterize the hybrid CNF-glass composites via appropriate material property and screening analysis.In addition to the research on novel hybrid composites, other material systems will be explored as appropriate to the support of the ongoing research program.
Project Methods
Drying cellulose nanofibrilsSpray drying CNF suspensions into powders for extrusion compounding will be a key technology for the research program. Pilot-scale spray drying equipment is available at the FBRI Technology Research Center in Old Town. Spray drying allows CNF suspensions to be simultaneously silane treated (functionalized) and dried prior to compounding with polymer matrices.Surface functionalizationSurface modification of the CNF fibers is expected to improve the nanomaterials matrix interface and enhance stress transfer and the final properties. The final properties of these composites will be compared to the corresponding composites without surface treatment or other additives. Processing of NanocompositesA key technical challenge for renewable nanocomposites is obtaining good dispersion of the nano fillers within a polymer matrix. The dry CNF and glass fibers will be compounded with polymer blends (PP, PLA, TPO) using a lab-scale twin-screw extrusion system to produce pellets (CW Brabender Instruments Inc., Hackensack, NJ, USA) at the Advanced Structures and Composites Center. All extruded compounds (pellets) will be dried again at 205°C for 4 hours and injected molded into flexural, tensile, or impact testing specimens using a lab mini-injector. For 3D printing, filaments of the compounds will be made utilizing the filament winder at the Composites Center. Proper statistical methods are important to quantify the degree of mixing. After taking scanning or transmission electron microscopy images of the nanofiller dispersion, statistical methods can be used to quantify filler dispersion (Moon et al. 2011). One of the research tasks will be to look at methods to quickly characterize the degree of mixing and filler dispersion within these nanocomposites.A 3D printer will be used for studying additive manufacturing using the hybrid CNF-glass nanocomposite compounds. A Makerbot Replicator 2X Experimental 3D Printer (MakerBot Industries, LLC, NY, USA) is a fused deposition modeling-based manufacturing technique. To make printed test parts, STL files of the CAD drawing of the test part are opened in the Makerware software (Version: 3.9.0), centered, laid flat and printed with the printer extrusion nozzle. Printing parameters can be modified in the "settings" software. A complete overlap between two adjacent hybrid nanocomposite compound filaments can be achieved with proper printer settings. Infill density will be set to 100% to make solid testing samples. The number of shells can be reduced to minimize influence on the part mechanical properties.Material Property CharacterizationPrepared hybrid CNF-glass nanocomposite sample materials will be tested according to the appropriate ASTM standards for flexure, tensile, impact, and coefficient of thermal expansion. Injection molding and 3D printing will be used to prepare test specimens as appropriate to material testing needs.Thermal ExpansionThe specimens from each formulation will be tested in accordance with ASTM D 696: "Standard test method for coefficient of linear thermal expansion of plastics between -30 °C and 30 °C". A total of five (5) replicates will be tested using a vitreous submerged into a temperature controlled bath. Each specimen will be exposed to a steady-state temperature of -30 °C and 30 °C, with the change in length recorded for analysis. This change in length will be used to calculate the coefficient of thermal expansion (based on the change in length per degree temperature change).Screening Analysis Tools Several analytical tools will be used to screen the hybrid nanocomposite materials including: scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA).Scanning Electron Microscopy (SEM) Scanning Electron Microscopy (SEM) uses a focused electron beam to scan small areas of solid samples. Secondary electrons are emitted from the sample and are collected to create an area map of the secondary emissions. Since the intensity of secondary emission is very dependent on local morphology, the area map is a magnified image of the sample. Spatial resolution is as high as 1 nanometer for some instruments, but 4 nm is typical for most. Magnification factors can exceed 300,000X. Because the SEM utilizes vacuum conditions and uses electrons to form an image, special preparations must be done to the sample. All water must be removed from the samples because the water would vaporize in the vacuum. All metals are conductive and require no preparation before being used. All non-metals need to be made conductive by covering the sample with a thin layer of conductive material (i.e. gold or palladium).In the project, SEM will be used for the following analysis:Low, intermediate and high resolution images of the morphology features of the hybrid nanocomposites obtained using CNF, glass, and polymerDegree of agglomeration or level of distribution of the nanocellulose (obtained from different processes, pre-treated with coupling agent and/or chemically modified) in the matrix.Thermogravimetric analysis (TGA):TGA is a thermodynamic technique that involves heating a sample while monitoring the weight simultaneously. It is used to study the thermal decomposition of materials and the kinetic rates of decomposition. This decay rate will most likely be monitored in an isothermal mode (constant temperature). This is more inductive to the parameters typically seen during extrusion. The degradation temperature of nanocellulose, polymer, and all other components in the formulation mix is important information for process parameter determination and product evaluation.Differential scanning calorimetry (DSC):DSC is used for analyzing fusion, crystallization, melting behavior, and glass transition temperature. It is important to evaluate the thermal behavior when materials are heated/cooled. Melting temperature is an important value for process and thermal stability of the product.Dynamic Mechanical Thermal Analysis (DMTA):The viscoelastic properties such as the storage modulus (E') and the mechanical loss factor (E"), damping ratio (E"/E') will be recorded as a function of temperature and frequency.Statistical AnalysisThroughout the experimental process, parameter and testing level decisions will be selected based on sound design of experiment (DOE) techniques. Material loading levels will be uniform and evenly distributed to aid in statistical comparison purposes. Some of the anticipated statistical comparisons are:Statistical comparison of nanocomposite formulation treatment effects on material propertiesMechanical properties of manufactured composite vs. fiber loading level