Thermal diffusivity and secondary crystallisation kinetics in poly(lactic acid)

Marsh, Joseph; Turner, Richard; Carter, J.; Jenkins, Michael J.

doi:10.1016/j.polymer.2019.121595

Cited by 17 publications

(13 citation statements)

References 36 publications

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“…As far as the heat transport via the polymer was concerned, this was quite poor in the amorphous polymers and became worse when filler-polymer interfaces were involved [22,23]; the latter acting as heat scatterers. On the contrary, the formation of crystals (ordered structures) is known to favor polymerthrough transport of hot phonons [45,46]. This was clear in our case when comparing the amorphous and highly crystalline matrices in Figure 8.…”

Section: Thermal Conductivity (Lfa)mentioning

confidence: 59%

“…In the HDPE-based systems compared with the PS-based ones, α and λ were larger and this was most probably due to the implementation of polymer HDPE crystals at high fractions [22,33,45,46,71]. In Figure 8a, the % increase in CF was not equal or similar to the increase of α and λ.…”

Section: Thermal Conductivity (Lfa)mentioning

confidence: 89%

“…As expected in neat polymers, heat transport occurs via a weak diffusion of phonons and thus results in low α and λ. The situation improves with the implementation of polymer crystals [45,46]. A variety of effects mainly concerning scatterings of the thermal carriers at interfaces, i.e., polymer-fillers and filler-fillers are also involved in PNCs [40,41,47,48].…”

Section: Introductionmentioning

confidence: 99%

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Effects of Expandable Graphite at Moderate and Heavy Loadings on the Thermal and Electrical Conductivity of Amorphous Polystyrene and Semicrystalline High-Density Polyethylene

et al. 2021

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In this work, we prepared and investigated two series of polymer composites, wherein the matrix was either an amorphous polystyrene (PS) or a semicrystalline high-density polyethylene (HDPE) filled with expandable graphite (EGr) at relatively high loadings within the range 5–55 wt %. For the investigation we employed a thermogravimetric analysis and differential scanning calorimetry to assess the thermal transitions and evaluate the various polymer fractions (crystalline (CF), mobile (MAF) and rigid amorphous (RAF)) in addition to broadband dielectric spectroscopy and a laser flash analysis to evaluate the EGr effects on electrical conductivity, σ, and thermal conductivity, λ, respectively. In PS, EGr was found to impose an increase of the glass transition temperature and a systematic decrease of the corresponding heat capacity change. The latter was rationalized in terms of the formation of an interfacial RAF. No glass transition was recorded for HDPE whereas the fillers increased the CF moderately. As expected, σ increased with the filler loading for both matrices, up to 10−3–10−2 S/cm, resulting in a conductive percolation threshold for electrons at > 8 wt % EGr. Simultaneously, the λ of PS and HDPE were strongly increased, from 0.13 and 0.38 W·K–1·m–1 up to 0.55 and ~2 W·K–1·m–1, respectively. λ demonstrated an almost linear EGr loading dependence whereas the semicrystalline composites exhibited a systematically higher λ.

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Section: Thermal Conductivity (Lfa)mentioning

confidence: 59%

Section: Thermal Conductivity (Lfa)mentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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Effects of Expandable Graphite at Moderate and Heavy Loadings on the Thermal and Electrical Conductivity of Amorphous Polystyrene and Semicrystalline High-Density Polyethylene

et al. 2021

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“…In a series of recent papers [22,26,28], it has been shown that the Avrami model can be modified to successfully account for a secondary crystallisation process. The modification is based on the idea that the secondary process develops with the square root of time.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, as the thickness of the lamellae is greater at the centre of the spherulite, it was postulated that secondary crystallisation occurs as soon as the lamellae has been formed and proceeds with and beyond the primary process [22]. These factors have led to the formation of a new model for the crystallisation of polymers, which has been validated using infra-red spectroscopy [22,26] and laser flash analysis [28].…”

Section: Introductionmentioning

confidence: 99%

The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry

et al. 2019

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This paper demonstrates the application of a modified Avrami equation in the analysis of crystallisation curves obtained using differential scanning calorimetry (DSC). The model incorporates a square root of time dependence of the secondary process into the conventional Avrami equation and, although previously validated using laser flash analysis and infrared spectroscopy, is not currently transferable to DSC. Application of the model to calorimetric data required long-duration isotherms and a series of data treatments. Once implemented, the square root of time dependence of the secondary process was once again observed. After separation of the secondary process from the primary, a mechanistic n value of 3 was obtained for the primary process. Kinetic parameters obtained from the analysis were used in the model to regenerate the fractional crystallinity curves. Comparison of the model with experimental data generated R 2 values in excess of 0.995. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was used as model polymer due to the prominent secondary crystallisation behaviour that this polymer is known to display.The crystallisation kinetics of a polymer are generally described by the following Avrami equation [15]:where X p,t is the fractional primary crystallinity; X p,∞ is the final primary crystallinity; Z p is the Avrami primary crystallisation rate constant; t is time and n an integer combining values attributed to both the geometry and mechanism of nucleation. Although this equation is widely used, it often generates non-integer n values. In addition, it does not take into account the secondary crystallisation process, which has been proven to occur during polymer crystallisation [16][17][18][19]. Numerous authors have proposed modifications to the Avrami equation to account for these issues, with the most notable being Hillier [20,21], Velisaris [17] and Hay [22].The method developed by Hillier [20] assumes an initial constant radial growth of spherulites, followed by a first-order increase in crystallinity at time θ. This leads to the standard Avrami equation for the primary process (Equation (1)) and a modified version for the secondary process (Equation (2)) in which the n exponent is taken as 1:where X s,t−θ is the fractional crystallinity formed after time θ; X s,∞ is the final fractional crystallinity; and z s is the secondary rate constant. These two equations can then be combined to give an expression for the total crystallinity at time t. X t = X p,t + t 0

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A Versatile Disorder‐to‐Order Technology to Upgrade Polymers into High‐Performance Bioinspired Materials

Liu

Chen

et al. 2023

Adv Healthcare Materials

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Biodegradable polymer as traditional material has been widely used in the medical and tissue engineering fields, but there is a great limitation as to its inferior mechanical performance for repairing load‐bearing tissues. Thus, it is highly desirable to develop a novel technology to fabricate high‐performance biodegradable polymers. Herein, inspired by the bone's superstructure, a versatile disorder‐to‐order technology (VDOT) is proposed to manufacture a high‐strength and high‐elastic modulus stereo‐composite self‐reinforced polymer fiber. The mean tensile strength (336.1 MPa) and elastic modulus (4.1 GPa) of the self‐reinforced polylactic acid (PLA) fiber are 5.2 and 2.1 times their counterparts of the traditional PLA fiber prepared by the existing spinning method. Moreover, the polymer fibers have the best ability of strength retention during degradation. Interestingly, the fiber tensile strength is even higher than those of bone (200 MPa) and some medical metals (e.g., Al and Mg). Based on all‐polymeric raw materials, the VDOT endows bioinspired polymers with improved strength, elastic modulus, and degradation‐controlled mechanical maintenance, making it a versatile update technology for the massive industrial production of high‐performance biomedical polymers.

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Thermal diffusivity and secondary crystallisation kinetics in poly(lactic acid)

Cited by 17 publications

References 36 publications

Effects of Expandable Graphite at Moderate and Heavy Loadings on the Thermal and Electrical Conductivity of Amorphous Polystyrene and Semicrystalline High-Density Polyethylene

Effects of Expandable Graphite at Moderate and Heavy Loadings on the Thermal and Electrical Conductivity of Amorphous Polystyrene and Semicrystalline High-Density Polyethylene

The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry

A Versatile Disorder‐to‐Order Technology to Upgrade Polymers into High‐Performance Bioinspired Materials

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