Development of a Bead Foam from an Engineering Polymer with Addition of Chain Extender: Expanded Polybutylene Terephthalate

Standau, Tobias; Hädelt, Bianca; Schreier, Peter; Altstädt, Volker

doi:10.1021/acs.iecr.8b04799

Cited by 50 publications

(79 citation statements)

References 42 publications

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“…Chain extenders are widely used in the polymer industry, especially in the recycling industry, due to the chain degradation during processing at high temperatures and the resulting loss of properties [1]. Furthermore, they are often used in polymer foaming processes to increase the melt-strength of polyesters and polyamides to enhance the foamability and moldability of bead foams [2][3][4]. During chain extension a bi-or multifunctional reactant reacts with the end groups of polycondensates and the molecular weight increases [5].…”

Section: Introductionmentioning

confidence: 99%

Rheological Study of Gelation and Crosslinking in Chemical Modified Polyamide 12 Using a Multiwave Technique

2020

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When processing particular polymers, it may be necessary to increase the molecular weight, for example, during polymer recycling or foaming. Chemical additives such as chain extenders (CE) are often used to build up the molecular weight during reactive extrusion. One issue of chain extenders, however, is that they can cause gelation or crosslinking of the polymer during processes with long residence times. This can lead to strong process fluctuations, undesired process shutdowns due to uncontrollable torque and pressure fluctuations and finally consistent material quality cannot be guaranteed. To measure and understand the reactivity between the polymer and the CE a rheological test can help. However, the standard gel point evaluation used for thermosets by examining the point of intersection of storage- and loss modules is not suitable, as this method is frequency-dependent. This study uses a multiwave rheology test to identify the gel-point more reliably. Both evaluation methods were compared on a polyamide 12 system, which is modified with an industrially relevant chain extender. The results show that the multiwave test can be applied on a chemical modified thermoplastic system and that the material system indicates a general tendency to crosslink. The frequency-independent gel-point evaluation shows that the gel-point itself is dependent on the processing temperature. Finally, it was possible to detect undesired side reactions, which are not recognizable with the standard testing method. Both findings are directly relevant for the reactive extrusion process and help to understand the mechanism of gelation.

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Section: Introductionmentioning

confidence: 99%

Rheological Study of Gelation and Crosslinking in Chemical Modified Polyamide 12 Using a Multiwave Technique

2020

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“…Even though it is often stated in literature that the melt strength plays a vital role in the foaming of PLA, only a few publications actually quantify it at all [7][8][9][10]. An increased melt strength is beneficial for foaming, as it prevents coalescence and rupture during the cell growth step because the cell walls can withstand higher forces during stretching while expanding and can consequently lead to an improved expansion behavior (i.e., lower density and finer cells) [11].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)

et al. 2020

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In this comprehensive study, the influence of (i) material specific properties (e.g., molecular weight, zero shear viscosity, D-content) and (ii) process parameters (e.g., saturation temperature, -time, -pressure, and pressure drop rate) on the expansion behavior during the autoclave foaming process were investigated on linear Polylactide (PLA) grades, to identify and evaluate the foam relevant parameters. Its poor rheological behavior is often stated as a drawback of PLA, that limits its foamability. Therefore, nine PLA grades with different melt strength and zero shear viscosity were systematically chosen to identify whether these are the main factors governing the foam expansion and whether there is a critical value for these rheological parameters to be exceeded, to achieve low density foams with fine cells. With pressure drop induced batch foaming experiments, it could be shown that all of the investigated PLA grades could be foamed without the often used chemical modifications, although with different degrees of expansion. Interestingly, PLAs foaming behavior is rather complex and can be influenced by many other factors due to its special nature. A low molecular weight combined with a high ability to crystallize only lead to intermediate density reduction. In contrast, a higher molecular weight (i.e., increased zero shear viscosity) leads to significant increased expandability independent from the D-content. However, the D-content plays a crucial role in terms of foaming temperature and crystallization. Furthermore, the applied process parameters govern foam expansion, cell size and crystallization.

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“…Both cases give foams having high densities and inhomogeneous and coarse cell morphology [ 5 ]. Therefore, improving the rheological properties of these polymers is crucial [ 6 ]. To address this issue, several strategies have been developed to improve the melt viscosity and melt strength as well as the strain hardening (extensional thickening) behavior, which is mainly caused by increased molecular weight and intrinsic entanglements in the polymer melt.…”

Section: Introductionmentioning

confidence: 99%

“…To address this issue, several strategies have been developed to improve the melt viscosity and melt strength as well as the strain hardening (extensional thickening) behavior, which is mainly caused by increased molecular weight and intrinsic entanglements in the polymer melt. Additional entanglements as well as an increase in molecular weight can be introduced by post-polymerization modification reactions such as partial crosslinking [ 7 ], long-chain branching and chain extension [ 6 , 8 , 9 , 10 , 11 , 12 ]. Chain extension or branching has been mostly used for the semicrystalline polyesters, PET and PBT [ 6 , 13 , 14 ].…”

Section: Introductionmentioning

confidence: 99%

“…Additional entanglements as well as an increase in molecular weight can be introduced by post-polymerization modification reactions such as partial crosslinking [ 7 ], long-chain branching and chain extension [ 6 , 8 , 9 , 10 , 11 , 12 ]. Chain extension or branching has been mostly used for the semicrystalline polyesters, PET and PBT [ 6 , 13 , 14 ]. As reagents for the post-polymerization modification reactions, cyclic anhydrides [ 15 , 16 ], oxazolines [ 12 ], carbodiimides [ 17 ], isocyanates and epoxides [ 18 , 19 ] are often used, which react with the hydroxyl and carboxyl end groups of the polyester.…”

Section: Introductionmentioning

confidence: 99%

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Low-Density Polybutylene Terephthalate Foams with Enhanced Compressive Strength via a Reactive-Extrusion Process

et al. 2020

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Due to their appealing properties such as high-temperature dimensional stability, chemical resistance, compressive strength and recyclability, new-generation foams based on engineering thermoplastics such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) have been gaining significant attention. Achieving low-density foams without sacrificing the mechanical properties is of vital importance for applications in the field of transportation and construction, where sufficient compressive strength is desired. In contrast to numerous research studies on PET foams, only a limited number of studies on PBT foams and in particular, on extruded PBT foams are known. Here we present a novel route to extruded PBT foams with densities as low as 80 kg/m3 and simultaneously with improved compressive properties manufactured by a tandem reactive-extrusion process. Improved rheological properties and therefore process stability were achieved using two selected 1,3,5-benzene-trisamides (BTA1 and BTA2), which are able to form supramolecular nanofibers in the PBT melt upon cooling. With only 0.08 wt % of BTA1 and 0.02 wt % of BTA2 the normalized compressive strength was increased by 28% and 15%, respectively. This improvement is assigned to the intrinsic reinforcing effect of BTA fibers in the cell walls and struts.

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Development of a Bead Foam from an Engineering Polymer with Addition of Chain Extender: Expanded Polybutylene Terephthalate

Cited by 50 publications

References 42 publications

Rheological Study of Gelation and Crosslinking in Chemical Modified Polyamide 12 Using a Multiwave Technique

Rheological Study of Gelation and Crosslinking in Chemical Modified Polyamide 12 Using a Multiwave Technique

Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)

Low-Density Polybutylene Terephthalate Foams with Enhanced Compressive Strength via a Reactive-Extrusion Process

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