Dramatic Improvements in Strain Hardening and Crystallization Kinetics of PLA by Simple Reactive Modification in the Melt State

Nerkar, Manoj; Ramsay, J. O.; Ramsay, Bruce A.; Kontopoulou, Marianna

doi:10.1002/mame.201400078

Cited by 36 publications

(30 citation statements)

References 33 publications

(54 reference statements)

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“…PLA1/GMA also had lower nucleation activity, compared to the linear PLA (Figure 8). However in this material there is no strong evidence of crystallization [8], or shear-induced crystallization at 140°C (Figure 9) during the time frame of the experiment.…”

Section: Combined Branching and Nucleation Effect On Foamingmentioning

confidence: 74%

“…Whereas the non-isothermal properties of PLA1/GMA were not altered substantially compared to PLA1 (Table 1), the crystallinity of the material was higher than the parent PLA, and its crystallization half-time was lower [8]. PLA1/GMA also had lower nucleation activity, compared to the linear PLA (Figure 8).…”

Section: Combined Branching and Nucleation Effect On Foamingmentioning

confidence: 77%

“…This material demonstrates an intense exothermic peak, disappearance of the cold crystallization peak and higher crystallinity, together with significantly enhanced crystallization kinetics [8]. The highly branched chain population, characteristic of materials modified through this approach, may enhance crystallization as mentioned above.…”

Section: Combined Branching and Nucleation Effect On Foamingmentioning

confidence: 95%

“…Recent work in our group employed a simple reactive modification approach, utilizing solventfree, peroxide-initiated grafting of the multi-functional co-agent triallyl-trimesate (TAM) to introduce branching and achieve substantial improvements in the strain hardening characteristics of PLA [7,8]. This approach also resulted in faster crystallization kinetics, under both isothermal and non-isothermal conditions.…”

Section: Introductionmentioning

confidence: 96%

“…Incorporation of branching through reactive extrusion is a cost-effective and versatile means to enhance melt viscosity, molecular weight, and elasticity in PLA [4][5][6][7][8]. In terms of foam processing the improved melt strength, which hinders cell coalescence and prevents gas from escaping from the cells, results in decreased foam cell size, higher cell density, and increased expansion ratio [6,[9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

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Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization

Tiwary

Park

Kontopoulou

2017

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Section: Combined Branching and Nucleation Effect On Foamingmentioning

confidence: 74%

Section: Combined Branching and Nucleation Effect On Foamingmentioning

confidence: 77%

Section: Combined Branching and Nucleation Effect On Foamingmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization

Tiwary

Park

Kontopoulou

2017

European Polymer Journal

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Advances in peroxide‐initiated graft modification of thermoplastic biopolyesters by reactive extrusion

2021

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We report recent advances in the solvent‐free reactive extrusion of thermoplastic biopolyesters, in the presence of peroxide initiators and tri‐functional cross‐linking/ chain extending agents. The resulting compounds have improved processability and properties compared to the starting materials, including higher melt strength due to long‐chain branching, higher crystallinity, faster crystallization kinetics, and improved mechanical properties. We demonstrate that these strategies are effective in thermoplastic biopolyesters, such as poly(lactide) (PLA) and various poly(hydroxyalkanoates) (PHAs), including poly(hydroxybutyrate) (PHB), and medium‐chain length PHAs. In addition to the improvements in properties, this approach has significant benefits in polymer processing operations, including blend compatibilization, and foaming. We also demonstrate that crosslinked PLA particles prepared by reactive extrusion using peroxide and a tri‐functional coagent, serve as very effective nucleating additives, resulting in crystallization half‐times as low as 1 min, and heat deflection temperature as high as 140°C. These modifications do not have adverse effects on the hydrolytic degradation characteristics of PLA.

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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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Dramatic Improvements in Strain Hardening and Crystallization Kinetics of PLA by Simple Reactive Modification in the Melt State

Cited by 36 publications

References 33 publications

Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization

Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization

Advances in peroxide‐initiated graft modification of thermoplastic biopolyesters by reactive extrusion

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

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