Abstract:Nowadays, numerous techniques are used to quantify the resistance of cellular polymers against a thermal load. These techniques differ in significance and reproducibility and are all dependent on foam density, structure (i.e., cell size and -distribution) and sample geometry. Very different behaviors are expected for extrusion- and bead foams, as well as for amorphous and semi-crystalline polymers. Moreover, established tests use temperature ramps which would lead to temperature gradients within the sample and… Show more
“…[1][2][3] In particular, their enhanced thermal stability and mechanical resistance qualify them for use as construction materials in areas such as the automotive and electrical industries. [1,4,5] For lightweight structures, polyesters are used as foams to save weight while maintaining reliable mechanical properties. However, the foaming of these materials is challenging.…”
Polyesters, such as poly (butylene terephthalate) (PBT), owe a rather low melt strength, which is considered as not beneficial for foaming. To overcome this issue, a typical attempt is the incorporation of chemical modifications—so‐called chain extenders (CE)—in the reactive extrusion process. In this study, the reaction kinetic variables are investigated depending on the material and process parameters. For this purpose, different series of experiments are performed with varying PBT with different molecular weights and the commonly used CE, Joncryl ADR4468, on a micro compounder. The screw force is recorded and analyzed using an Avrami and an Arrhenius plot. First, the amount of CE is systematically varied. To study the course of the reaction in more detail, the reaction is stopped in a series of measurements (10, 30, 60, and 90 s after complete filling). Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT‐IR), and Raman spectra are recorded. In the second series, the effect of processing temperatures between 250 and 270 °C is investigated, and finally, in the third series, the average molecular weight of PBT is varied. It could be shown that the activation energy seems to be dependent on the initial molecular weight; lower molecular weights result in lower activation energy.
“…[1][2][3] In particular, their enhanced thermal stability and mechanical resistance qualify them for use as construction materials in areas such as the automotive and electrical industries. [1,4,5] For lightweight structures, polyesters are used as foams to save weight while maintaining reliable mechanical properties. However, the foaming of these materials is challenging.…”
Polyesters, such as poly (butylene terephthalate) (PBT), owe a rather low melt strength, which is considered as not beneficial for foaming. To overcome this issue, a typical attempt is the incorporation of chemical modifications—so‐called chain extenders (CE)—in the reactive extrusion process. In this study, the reaction kinetic variables are investigated depending on the material and process parameters. For this purpose, different series of experiments are performed with varying PBT with different molecular weights and the commonly used CE, Joncryl ADR4468, on a micro compounder. The screw force is recorded and analyzed using an Avrami and an Arrhenius plot. First, the amount of CE is systematically varied. To study the course of the reaction in more detail, the reaction is stopped in a series of measurements (10, 30, 60, and 90 s after complete filling). Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT‐IR), and Raman spectra are recorded. In the second series, the effect of processing temperatures between 250 and 270 °C is investigated, and finally, in the third series, the average molecular weight of PBT is varied. It could be shown that the activation energy seems to be dependent on the initial molecular weight; lower molecular weights result in lower activation energy.
“…The compression modulus is widely used in the literature to compare the linear elastic behavior of bead foams. 2,3,[6][7][8][9][10][11][12] However, an accurate automatic determination of E C has not been established, and therefore values for the same foam and conditions may vary depending on the laboratory where it was measured or even the person doing the manual determination of E C . For instance, for expanded polypropylene (EPP) foam with a density of 60 kg m À3 at room temperature, some reported values of E C (in MPa) include 3.34, 11 7.35, 6 and 8.34.…”
Section: Introductionmentioning
confidence: 99%
“…2,3,[6][7][8][9][10][11][12] However, an accurate automatic determination of E C has not been established, and therefore values for the same foam and conditions may vary depending on the laboratory where it was measured or even the person doing the manual determination of E C . For instance, for expanded polypropylene (EPP) foam with a density of 60 kg m À3 at room temperature, some reported values of E C (in MPa) include 3.34, 11 7.35, 6 and 8.34. 12 Among other problems, the manual determination of the maximum slope in the linear-elastic regime is prone to errors.…”
Section: Introductionmentioning
confidence: 99%
“…The compression modulus or elastic modulus () is the main parameter characterizing the linear‐elastic regime (region I in Figure 1) and is defined as the slope of the linear region in the stress–strain curve. The compression modulus is widely used in the literature to compare the linear elastic behavior of bead foams 2,3,6–12 . However, an accurate automatic determination of has not been established, and therefore values for the same foam and conditions may vary depending on the laboratory where it was measured or even the person doing the manual determination of .…”
In the realm of material characterization, the mechanical properties of polymer foams play a pivotal role in shaping their applicability across diverse industries. In this pursuit, we present a novel approach to standardize and automate the assessment of key mechanical parameters for Expanded Polypropylene (EPP) foams using a self‐developed Python script, made freely available for the scientific community. We precisely determine the compression modulus, plateau onset, and onset of densification strain for EPP foams across various densities. The script's effectiveness is demonstrated through comparisons with manual evaluations and established standards, highlighting its superiority, consistency, and suitability for a wide range of materials and conditions. Moreover, the script enables the analysis of energy absorption, shedding light on the intricate relationship between density and energy dissipation. Finally, our approach was extended to other foams to provide insight on their mechanical properties. The automated methodology ensures accuracy, reproducibility, and efficiency, thereby advancing the understanding of foam materials and facilitating informed design decisions. This research contributes to laying a foundation for the standardized assessment of foam mechanical properties, which could potentially facilitate their effective use in other applications.
“…[ 3 ] However, PBT bead foams are not commercially established yet, and common established bead foams based on polystyrene (PS), or polypropylene (PP), withstand only intermediate temperatures (80 °C for PS and 110 °C for PP). [ 8 ] The successful preparation of PBT bead foams (so‐called expanded PBT, E‐PBT) would enable both, low density and strong mechanical integrity at elevated temperatures for highly advanced materials.…”
Poly(butylene terephthalate) (PBT) is difficult to foam due to its unfavorable rheological behavior (low melt strength, no strain hardening). In particular, a high expansion and a homogeneous cell morphology are difficult to achieve. This can be altered successfully by addition of multifunctional chain extenders. Chain extenders cause nondefined and rarely understood changes in the polymer architecture usually described as branching. In this contribution, the synthesis of two series of PBT copolyesters with defined short-chain branched units is presented. Dilinoleic derivatives with linear C 9 and C 7 alkyl side chains are employed to reflect short-chain branches and are incorporated into PBT in various molar ratios. Characterization by NMR spectroscopy and size exclusion chromatography demonstrates the random chain structure and high molar masses of the terpolyesters. Incorporation of dilinoleic derivatives results in the reduction of PBT crystallinity, decreased glass transition temperatures, and altered rheological behavior, in particular of extensional rheology characterized by strain hardening. The comparison to control copolyesters without branches proves that strain hardening is caused by the branches. A higher concentration of branches induces stronger strain hardening, resulting in successful foaming. It is demonstrated that the new terpolyesters have properties comparable with PBT treated with chain extenders.
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