Effect of chemical modification on the thermal and rheological properties of polylactide

Göttermann, Svenja; Standau, Tobias; Weinmann, Sandra; Altstädt, Volker; Bonten, Christian

doi:10.1002/pen.24505

Cited by 27 publications

(36 citation statements)

References 19 publications

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“…The concentrations were selected based on pre-trials with 1.0 wt% for the chain extender and 0.2 wt m% for the peroxide. As described in a former study (25), the addition of the modifiers leads to an increase of molecular weight from 130,400 g/mol (neat PLA) to 200,600 g/mol (PLA+mEP) and 237,600 g/mol (PLA+PER), respectively. Also, topological changes of the polymer chains were described in our previous studies (25,30).…”

Section: Experimental 21 Materialssupporting

confidence: 58%

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Effects of chemical modifications on the rheological and the expansion behavior of polylactide (PLA) in foam extrusion

et al. 2019

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It is well known that polylactide (PLA) is difficult to foam due to its low melt strength. Thus, many ways were described in the literature to enhance the foamability. However, the melt strength was actually determined only in a limited number of publications. In this study, the addition of chemical modifiers was used to change the rheological behavior of PLA and thereby improve its foamability in foam extrusion process. For the first time the use of dicumyl peroxide modified PLA in foam extrusion is described. Both modifications lead to a distinct increase in melt strength. Here, the highest increase was shown for the PLA modified with dicumyl peroxide. Furthermore, strain hardening was observed for PLA modified with the peroxide. Low density foams were achieved for neat and modified PLA in foam extrusion. Neat PLA showed a density of 45 kg/m3, while the peroxide modified PLA showed the highest expansion with a density reduction down to 32 kg/m3. Both modifications result in a more uniform cell structure and an improved compression strength. Here, the foamed, peroxide modified PLA showed outstanding performance compared to neat PLA foam with twice the compression strength (151 Pa) even at a 30% lower density.

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Section: Experimental 21 Materialssupporting

confidence: 58%

“…The work of Södergård (24) showed that below 0.25 wt% branching is predominant while above 0.25 wt% significant crosslinking can be expected. In a former study (25) we could show, that thermal and rheological behavior significantly change by the addition of different chemical modifiers, like dicumyl peroxide.…”

Section: Introductionmentioning

confidence: 97%

Effects of chemical modifications on the rheological and the expansion behavior of polylactide (PLA) in foam extrusion

et al. 2019

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“…PLA is a hard, transparent, biodegradable, and biocompatible polymer that could be derived from ring‐opening polymerization of lactide . Despite the high modulus, high strength, excellent processability, and low energy dependence, the application of this polymer in processes involving melt stretching (film extrusion, blow molding, foaming, and the like) have been limited due to disadvantages such as intrinsic brittleness, slow crystallization rate, low melt strength, narrow processing window, and low thermal stability . The low melt strength of PLA is due to the inherent degradation behavior of polyesters.…”

Section: Introductionmentioning

confidence: 99%

Effect of Two‐Step Chain Extension using Joncryl and PMDA on the Rheological Properties of Poly (lactic acid)

Yahyaee

Javadi

Garmabi

et al. 2019

Macro Materials & Eng

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polymer in processes involving melt stretching (film extrusion, blow molding, foaming, and the like) have been limited due to disadvantages such as intrinsic brittleness, slow crystallization rate, low melt strength, narrow processing window, and low thermal stability. [7][8][9][10][11][12][13] The low melt strength of PLA is due to the inherent degradation behavior of polyesters. PLA degrades at temperatures above its melting point, similar to other polyesters. The degradation reactions include hydrolysis, inter-chain transesterification, and depolymerization by back-biting (intramolecular transesterification). Depending on the process conditions, one of these undesirable reactions overcomes the others. For example, the chain scission, at temperatures above the melting point, is responsible for the degradation of the polymer that leads to a decrease in molecular weight and rheological properties. [1,14,15] To obtain a wider processing window for PLA and thus make the range of its applications broader, improved melt strength is postulated. [16,17] For increasing the melt strength, the modification of PLA is an effective method to achieve a branched high molecular weight structure. Several ways exist for the branching of PLA, including solution polymerization, using the free radical initiator, and functional groups reaction. Due to environmental problems, high costs, low effectiveness, and issues associated with process convenience, solution reactions are not the best choices. Furthermore, as the free radical reaction is a random one, it is more difficult to control the molecular weight when utilizing this method. On the contrary, compared to the free radical branching, reactions of functional groups tend to give rise to long chain branching (LCB) more readily, leading to controlled structures. [18] Chainextension reactions are exploited to increase the melt strength of linear polymers. The advantage of using the chain extenders with functional groups includes re-bonding the degraded chains together and as a result, increasing the molecular weight and the melt strength. For polyesters such as PET and PLA, chain-extension occurs by increasing the molecular weight due to bridging the hydroxyl or carboxyl reactive-end groups using bi-or multi-functional molecules. [1,9] Some researchers have investigated the effect of different chain extenders with different functional groups such as diand multi-functional epoxides, [19][20][21][22][23][24][25][26][27] diisocyanate, [28][29][30] dianhydride, [31][32][33] and so forth. Among these, chain extenders constituted of multi-functional epoxy groups such as Joncryl are highly This research considers a two-step chain extension reaction in the presence of two chain extenders, Joncryl and Pyromellitic dianhydride (PMDA), as a solution for poor melt properties of poly (lactic acid) (PLA). The aim of adding PMDA is to increase the carboxyl groups via the anhydride ring-opening reaction so that the reaction between PLA and Joncryl could be facilitated since the reactivity between t...

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“…Typical modifiers that are used in combination with PLA can be distinguished by the occurring reaction into two groups: (i) functional group reactions and (ii) radical reactions and have been summarized in our previous work [4]. Additionally, the rheological as well as thermal behavior is influenced by the use of these modifiers [5]. The most common used modifier is the commercial additive Joncryl ® from BASF SE, which is a multi-functional epoxy based chain extender that reacts with the functional groups of PLA (i.e., carboxyl-and hydroxyl groups) during melt processing.…”

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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Effect of chemical modification on the thermal and rheological properties of polylactide

Cited by 27 publications

References 19 publications

Effects of chemical modifications on the rheological and the expansion behavior of polylactide (PLA) in foam extrusion

Effects of chemical modifications on the rheological and the expansion behavior of polylactide (PLA) in foam extrusion

Effect of Two‐Step Chain Extension using Joncryl and PMDA on the Rheological Properties of Poly (lactic acid)

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

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