8:00 am – 11:30 am:
TH9-Thermoplastic Materials and Foams: Fundamentals-Room S320G
8:00 am – 8:30 am:
Effect of Foam Density on Elastomeric Nanocomposite Foams Based on PolyisopreneRubber
Ali Vahidifar, University of Bonab
Elastomeric polyisoprene rubber nanocomposite foams were prepared via compression molding at different relative foam density 0.4, 0.5, 0.6 and 0.7. Effect of relative foam density on foam morphology and mechanical properties were studied. The results showed that degradation of chemical blowing agent Azodicarbonamide (ADC) and curing of IR compound occurred simultaneously. Light microscopy results showed that increasing foam density from 0.4 to 0.7 gave rise to a decrease in the average cell size from 530µm to 230µm while it led to an increase of cell density from 25 cell/mm3 to 195 cell/mm3. The compression behavior of foams was studied so as to calculate the normalized elastic modulus as a function of the relative density. Several models of cellular materials and polymer composites were used to understand and predict foams’ compression behavior. Results showed that Gibson Ashby model, having pressure parameters, had the best accordance with the experimental data.
8:30 am – 9:00 am:
Effect of Soft Segments and Nucleation Agents on the Properties of Thermoplastic Polyurethane Foam
Shu-Kai Yeh, National Taiwan University of Science and Technology
It is known that the properties of thermoplastic polyurethane (TPU) are related to its constituents. Different soft segments, hard segments and chain extenders offer different physical properties. However, very few studies have investigated the effect of the constituents on the properties of TPU foam. In this study, thermoplastic polyurethanes (TPUs) containing different soft segments were synthesized using a pre-polymer method. The samples were foamed, using CO2 as the blowing agent, by one-step batch foaming. The expansion ratio was controlled by varying the foaming temperature (Tf). The role of nucleation agents was also investigated. The shrinkage of the TPU foam was observed by monitoring the foam density. Due to the high diffusivity nature of CO2, significant shrinkage was observed within several hours. In our case, a stable expansion ratio of 4 times was observed.
9:00 am – 9:30 am:
Theoretical and Experimental Investigation of Bubble Growth in High-Pressure Foam Injection Molding
Chongda Wang, University of Toronto
We researched a novel simulation strategy that predicts bubble growth phenomenon tailored to high-pressure foam injection molding (HP-FIM) processes. This was done via systematic HP-FIM experiments using a visualization technique. The mathematical model that we developed was based on the well-known “cell model”. To improve the model’s robustness and accuracy, we used the Simha-Somcynsky equation of state for the PS/CO2 mixture, which in turn offers an accurate prediction of the initial bubble radius. Moreover, to capture the fluid flow and mass transport behavior during bubble growth, the transport and rheological properties (that is, its diffusion coefficient, surface tension, viscosity, and relaxation time) that were adopted in this work were functions of the temperature, the pressure, and the gas concentration. In this work, instead of solving the cavity temperature and pressure separately, the temperature and pressure profile inside the cavity were respectively simulated using MoldFlow and experimentally obtained. By inputting the initial gas concentration and the transient pressure and temperature profiles, the proposed model could accurately predict the bubble growth profile under different HP-FIM conditions. The proposed model was validated using experimental data obtained from a series of visualized HP-FIM trials. In both cases, qualitative and good quantitative agreements were achieved between the simulated and the measured bubble growth data.
9:30 am – 10:00 am:
Strain Hardening of LInear Polymer Enhanced by Heat Shrinking Fibers
Sundong Kim, University of Vermont
The strain hardening behavior of polymers has important roles in processing such as foaming, film formation, and fiber spinning. The most common method to enhance strain hardening is to introduce a long-chain branching structure on the backbone of a linear polymer, but this method is costly and challenging to tailor the behavior. We hypothesized that in situ shrinking fibers can increase the strain hardening of linear polymers, and the degree can be efficiently controlled. In this study, we show that heat-activated shrinking fibers compounded in linear polypropylene enhance strain hardening and foamability. Moreover, changing processing conditions, such as temperature, can amplify the degree of enhancement. Rheological measurements and physical foaming tests are shown to support our hypothesis.
10:00 am – 10:30 am:
Enhancing Electromagnetic Shielding Performance of PVDF/MWCNT Composites Through Foaming
Chenyinxia Zuo, University of Toronto
The relationship between Electromagnetic interference shielding effectiveness and void fraction of foamed PVDF polymer-based composites with 1 wt% MWCNTs is investigated in this paper. The specimens are prepared through the film casting, compression molding, and batch foaming processes. The composite is advantageous to EMI shielding when the foaming technique is incorporated to reduce weight. It is found out that a 0.62 ~ 0.96 g/cm3 composite achieves an overall EMI SE of 10.5 ~ 25.4 dB in the frequency range of 26 ~ 40 GHz, since increased interfacial surface area from internal gas bubbles contributes to a rise in EMI shielding via absorption.
10:30 am – 11:00 am:
Piezoelectric Foams with High Thermal Stability and Flexibility
Zhe Liu, Florida State University
This paper discusses the fabrication and characterization of a hybrid piezoelectric foams that exhibit high thermal stability whiling maintaining good flexibility.
11:00 am – 11:30 am:
Resorcinol Formaldehyde Aerogel Nano-network Structural Assembly and its Thermal Properties Correlation
Mohammed Alshrah, University of Toronto
When organic aerogel particles are polymerized, a complex three-dimensional (3-D) nano-network is generated. This network is composed of randomly assembled nanoparticles, which form many-branched nanoclusters with unique morphological features. The organic aerogels that result from this process have exceptional properties, which supersede those of the current materials used. We studied the morphological features of an organic aerogel (resorcinol-formaldehyde, RF) and correlated each feature to the sample thermal insulation properties. Several RF aerogels were synthesized with different morphological features and structural assemblies. This was done by changing the catalyst percentages and the void fractions at the polymerization stage. Then, each morphological feature was assessed and categorized using two scales: the macro scale and the micro scale. We found that the macro-features were independent of the catalyst percentages and depended only on the void fractions. However, the micro-features were highly sensitive to any changes during the polymerization process. These changes altered the samples’ three main structural factors: (i) The structural assembly, (ii) The porous structure, and (iii) The fractal parameters. Thus, we characterized and quantified each component within these areas. Then, we assessed the structure’s heat transfer modes and classified them as follows: (i) Solid conductivity through the solid particles, (ii) Gas conductivity through the gas molecules, and (iii) Thermal radiation. We identified the morphological features that governed each mode. For example, the samples’ solid conductivity was highly dependent on the fractal parameters of our structure; that is, the particles’ roughness, the structural complexity, and the structural homogeneity. For those samples with extremely rough particles and a complex structure, the solid conductivity reached the lowest possible point. We also found that the total thermal conductivity was mainly controlled by the micro-morphological features, and that the solid conductivity was the most dominant heat transfer mode.