Poly(lactic acid)-Based in Situ Microfibrillar Composites with Enhanced Crystallization Kinetics, Mechanical Properties, Rheological Behavior, and Foaming Ability

Abstract

Melt blending is one of the most promising techniques for eliminating poly(lactic acid)'s (PLA) numerous drawbacks. However, success in a typical melt blending process is usually achieved through the inclusion of high concentrations of a second polymeric phase which can compromise PLA's green nature. In a pioneering study, we introduce the production of in situ microfibrillar PLA/polyamide-6 (PA6) blends as a cost-effective and efficient technique for improving PLA's properties while minimizing the required PA6 content. Predominantly biobased products, with only 3 wt % of in situ generated PA6 microfibrils (diameter ≈200 nm), were shown to have dramatically improved crystallization kinetics, mechanical properties, melt elasticity and strength, and foaming-ability compared with PLA. Crucially, the microfibrillar blends were produced using an environmentally friendly and cost-effective process. Both of these qualities are essential in guarantying the viability of the proposed technique for overcoming the obstacles associated with the vast commercialization of PLA.

Investigation of rheology and morphology to follow physical fibrillar network evolution through fiber spinning of PP/PA6 blend fiber

“…Also, elongational viscosity measurements have shown the induction of strain hardening as a result of improved interface in fibrillar networks. The appearance of secondary plateau and strain hardening due to the fibrillar morphology have been observed for the systems composed of PET, PTFE, PBT, PS, and PA6 .…”

An Insight into Phenomenology of Polytrimethylene Terephthalate Fibrillation

“…Here, it may be deduced that temperature plays a crucial role in fibrillation threshold which can be seen that fibrillation shifts to 1 wt% of PTT in the fiber spun at 240 °C, which is not the case in previous works conducted at temperature below the T m of dispersed phase 30,39,45,47. According to the reported works, since viscosity ratio and processing conditions are under control of disperse‐phase ratio and temperature respectively, the fibrillation of each polymer blend system is also dependent, whose dependent fibrillation appears by forming fibrils with different lengths 2,14,18,28,30,31,36,38,47,51…”

“…Influence of Fibril Diameter and Length on Linear Melt Viscoelastic Behavior : According to the observed linear melt viscoelastic responses of samples, it is obvious that upon transition from spherical shape to elongated structure the terminal trend of storage modulus in the low‐frequency region is replaced with non‐terminal behavior 28–30,39. This behavior appears as a widened secondary plateau in the low‐frequency region and the more the fibril elongates, the more the fibril penetrates into the matrix and consequently, frequency independency becomes broadened 13,31–34,36…”

“…[28][29][30]39] This behavior appears as a widened secondary plateau in the low-frequency region and the more the fibril elongates, the more the fibril penetrates into the matrix and consequently, frequency independency becomes broadened. [13,[31][32][33][34]36] Fiber spinning as a potent method to impose the highest amount of elongational field makes the dispersed phase experience the highest elongational field to be transferred into elongated morphology. Although it has been observed that low amount of dispersed phase (1 [29] and 6 wt% [45] ) (due to high interfacial stress) is incapable of being elongated, increasing the processing temperature enables the PTT droplet to be fibrillated even at 1 wt% of PTT, which did not represent a suitable fibrillar morphology [29] at spinning temperature of 195 °C (Figure 6a at 240 °C).…”

“…Melt viscoelastic properties of the reported polymer blend systems have been mainly extracted via oscillatory rheometry. Although several works reported the appearance of a non‐terminal trend in the low‐frequency region13,28–30,36 by oscillatory tests performed in linear region, the growth of the physical fibrillar network (PFN) was observed as a secondary plateau in the low‐frequency region 23,25–27,29,30,37a,b. In addition, extensional viscometry test has also been utilized to observe the effect of in situ generation of elongated dispersed phase, and it was reported that strain hardening is the consequence of forming fibrils in situ whose growth depends on shear rate and time 33,28…”