Characterisation of multi-extruded poly(lactic acid)

Abstract. In this work the effect of multiple reprocessing was studied on molecular structure, morphology and properties of poly(lactic acid)/hydrotalcites (PLA/HT) nanocomposites compared to neat PLA. In addition, the influence of two different kinds of HT -organically modified (OM-HT) and unmodified (U-HT) -was evaluated. Thermo-mechanical degradation was induced by means of five subsequent extrusion cycles. The performance of the recycled materials was investigated by mechanical and rheological tests, differential scanning calorimetry (DSC), intrinsic viscosity measurements and SEM observation. The results indicated that the best morphology was achieved in the systems incorporating OM-HT. On increasing the extrusion reprocessing cycles, the properties showed behavior due to two opposite effects: i) chain scission due to thermo-mechanical degradation and ii) filler dispersion effect resulting from multiple processing. In particular, at low reprocessing cycles, both tensile and rheological properties seem to be mainly affected by HT dispersion, especially when OM-HT was added. After five reprocessing cycles, on the contrary, chain scission, i.e. thermo-mechanical degradation, dominated. As regards the effect of the presence of organic modifier in HT, the results indicated that this variable apparently did not affect the macroscopic performance of the nanocomposites, especially at high reprocessing cycles.

Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure-properties relationships in melt reprocessed PLA/hydrotalcites nanocomposites

Scaffaro¹,

Sutera²,

Mistretta³

et al. 2017

“…The observed decrease in the mechanical properties of unfoamed extruded PLA in comparison to the unfoamed virgin PLA might be because of the molecular weight degradation of extruded PLA during extrusion by shear and thermal exposure. Decrease in molecular weight during extrusion and hence a decrease in mechanical properties has also been reported by some other researchers [1,24]. Figure 9 shows the specific notched impact strength of the foamed and unfoamed samples.…”

Section: Mechanical Propertiessupporting

confidence: 77%

Biocomposites based on poly(lactic acid)/willow-fiber and their injection moulded microcellular foams

Zafar¹,

Zarrinbakhsh²,

Mohanty³

et al. 2016

Abstract. Natural fiber reinforced biocomposites have recently attracted many researchers because of their biodegradability, cost effectiveness and ecofriendliness. The present study investigates the properties of willow-fiber reinforced poly(lactic acid) based composites and their foam processability. Microcellular foams of the composites were prepared by foam injection moulding using nitrogen gas as the blowing agent. The effects of willow-fiber addition on the morphology, mechanical properties, thermal stability, crystallization, and heat deflection temperature (HDT) were studied. At 30 weight percent [wt%] willow-fiber content, unfoamed composites showed good improvement in specific tensile and flexural moduli. Addition of willow-fiber increased crystallinity and the rate of crystallization and yielded narrow crystallite size distribution as observed by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) results of the foamed composites revealed that increase in willow-fiber content caused smaller average cell size and higher cell density. Specific notch impact strength of foamed composites at both 20 and 30 wt% willow-fiber content showed increasing trend compared to that of their unfoamed counterparts.

“…In addition, only the tensile modulus remained constant with the thermo-mechanical cycles, whereas tensile strength and elongation at a break decreased after the thermo-mechanical treatment. The effect of a multi-extrusion process on the tensile properties, impact strength, melt flow index, and permeability of water vapor and oxygen of PLA was reported [47]. The results showed that the tensile strength and impact strength of PLA decreased slightly after the multi-extrusion process, whereas the melt flow index and permeability of water vapor and oxygen were increased by the multiextrusion cycles.…”

Section: Thermal Propertiesmentioning

confidence: 99%

Properties and medical applications of polylactic acid: A review

Hamad¹,

Kaseem²,

Yang

et al. 2015

601

306

Abstract. Polylactic acid (PLA), one of the well-known biodegradable polyesters, has been studied extensively for tissue engineering and drug delivery systems, and it was also used widely in human medicine. A new method to synthesize PLA (ring-opening polymerization), which allowed the economical production of a high molecular weight PLA polymer, broadened its applications, and this processing would be a potential substitute for petroleum-based products. This review described the principles of the polymerization reactions of PLA and, then, outlined the various materials properties affecting the performance of PLA polymer, such as rheological, mechanical, thermal, and barrier properties as well as the processing technologies which were used to fabricate products based on PLA. In addition, the biodegradation processes of products which were shaped from PLA were discussed and reviewed. The potential applications of PLA in the medical fields, such as tissue engineering, wound management, drugs delivery, and orthopedic devices, were also highlighted.