A Quantitative Study on Branching Density Dependent Behavior of Polylactide Melt Strength

Abstract

Polymer melt strength (MS) is strongly correlated with its molecular structure, while their relationship is not very clear yet. In this work, designable long‐chain branched polylactide (LCB‐PLA) is prepared in situ by using a tailor‐made (methyl methacrylate)‐co‐(glycidyl methacrylate) copolymer (MG) with accurate number of reactive sites. A new concept of branching density (φ) in the LCB‐PLA system is defined to quantitively study their relationship. Importantly, a critical point of φc = 5.5 mol/104 mol C is revealed for the first time, below which the zero‐shear viscosity (η0) corresponding to MS increases slowly with a slope of Δη0/Δφ = 1400, while it increases sharply above this critical point due to entanglement of neighboring LCB‐PLA chains. Consequently, the MS of PLA increased by >100 times by optimizing the LCB structures while maintaining processibility. Therefore, this work provides a deeper understanding and feasible route in quantitative design of polymers with high(er) melt strength for some specialty applications.

Extruded polylactide bead foams using anhydrous supercritical CO2 extrusion foaming

“…The viscoelastic properties are critical factors that have a significant influence on the foaming capacity of the PLA 27 . Typically, molten properties influenced the pore structures and morphologies of polymer foams during the extrusion foaming process, which could be generally improved by the chain extender 28 . The dynamic rheological properties of the PLA were studied at 190°C.…”

“…27 Typically, molten properties influenced the pore structures and morphologies of polymer foams during the extrusion foaming process, which could be generally improved by the chain extender. 28 The dynamic rheological properties of the PLA were studied at 190 C. As shown in Figure 1a, compared with pure PLA (PLA/CE-0), the storage modulus for the modified PLA by adding the chain extender of 0.5 and 1.0 wt% (PLA/CE 0.5, and PLA/CE-1.0) was significantly enhanced. This result was led by the more complex winding behavior of the PLA molecular chain after being modified by a chain extender.…”

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives

“…The linear molecular structure of PLA together with its weak crystallization ability and low molecular weight are disadvantages that hinder the application of PLA in the foaming field. Chain extension and branching are commonly used methods to increase PLA's molecular weight and improve PLA's foaming behaviour [280,281]. The chain extension reactions through the formation of ramifications and/or crosslinking structures makes it possible to increase the molecular weight of the polymer and thus also its viscosity, allowing for the improvement in the melt strength in order to reduce the loss of the blowing agent gas and prevent cell coalescence during foaming.…”

Simultaneously Enhanced Stereocomplexation and Melt Strength by Dynamic Polylactide toward Heat-Resistant Green Foams

“…Another burning question is how to enhance the melt strength of sc-PLA. Due to the linear molecular chain structure of PLA and the large number of ester groups, the molecular chains are not easily entangled, resulting in a low melt strength. − Even worse, the high processing temperature makes the viscosity of sc-PLA decrease sharply after melting. The extremely low melt strength makes the foaming of sc-PLA an almost impossible task. , The poor foamability and sc crystallization of sc-PLA result in the heat-resistant PLA foam be still challenging.…”