Comparison of thermal, structural and morphological properties of poly(L-lactide) and poly(L-lactide)/hydroxyapatite microspheres for laser sintering processes

Krokos, Anna; Gazińska, Małgorzata; Kryszak, Bartłomiej; Dzienny, Paulina; Stępak, Bogusz; Olejarczyk, Michał; Gruber, Piotr; Kwiatkowski, Ryszard; Bondyra, Agnieszka; Antończak, Arkadiusz J.

doi:10.14314/polimery.2020.9.2

Cited by 10 publications

(14 citation statements)

References 22 publications

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“…The additional transition point is sometimes identified, such as temperature of first detectable deviation from the interpolated baseline, as we further denoted as Tm beginning for melting. We had proposed to use Tm beginning , as temperature of beginning of melting endotherm, in place of onset [26]. The melting of semicrystalline polymers is a very broad process and onset temperature doesn't take into account the shape of leading edge of polymer melting peak.…”

Section: Thermal Properties Of Microspheresmentioning

confidence: 99%

“…Figure 7 shows a summary of the WAXD diffractograms of the PLA (A) and PLLA (B) microspheres. The course of the curves is characteristic of polylactide [26,31].…”

Section: Thermal Conductivity Of Microspheresmentioning

confidence: 99%

“…A detailed deconvolution of the curves into diffraction peaks and diffusion maxima was made. When carrying out this procedure, the literature reports were followed [26,48,49]. Figure 7 A', B' shows two examples for PLLA and PLA powders annealed at 40°C (a complete breakdown of deconvolution is provided in the Supplementary Materials in Figure S5).…”

Section: Thermal Conductivity Of Microspheresmentioning

confidence: 99%

“…Moreover, due to crystal polymorphism of PLLA, the reorganization of conformationally disordered α′-crystals into stable α-crystals occurs on heating. In our previous paper we precisely describe SW determination for PLLA and composite PLLA/HAP microspheres [26]. The research was focused on the influence of HAP particles on SW range.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Thermal Annealing on Sinterability of Different Grades Polylactide Microspheres Dedicated for Laser Sintering

Gazińska¹,

Krokos²,

Kryszak³

et al. 2021

Preprint

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Comparison of the influence of conditioning temperature of microspheres made of medical grade poly(L-lactide) (PLLA) and polylactide with 4wt.% of D-lactide content (PLA), on its thermal and structural properties is presented. The microspheres were fabricated by solid-in-oil-in-water method for application in additive manufacturing. The microspheres were annealed below glass transition temperature (Tg), above Tg but below onset of cold crystallization, and at two temperatures selected from the range of cold crystallization corresponding to crystallization of α’ and α form of poly(L-lactide) respectively, i.e., at 40°C, 70°C, 90°C and 120°C, in order to verify the influence of conditioning temperatures on sinterability of microspheres set as sintering window (SW). Based on differential scanning calorimetry measurements SW of microspheres were evaluated with consideration of existence of cold crystallization and reorganization of crystal polymorph. The results indicate that the conditioning temperature influence on availability and range of SW that depending on the D-lactide presence. We postulate the need for an individual approach for polylactide powders in determining the SW as a temperature range free of any thermal events. Moreover, other core powder characteristic, such as residual solvent content, morphology, particle size distribution, powder flowability and thermal conductivity, as a key property for successful laser sintering, are characterized. The microspheres are close to sphere and the size of microspheres are below 100 µm. Residual solvents content decreases with the increase of annealing temperature. The thermal conductivity is 0.073 W/mK and 0.064 W/mK for PLA and PLLA microspheres, respectively, and it depends on the spherical shape of the microspheres. Furthermore, the WAXD studies prove that an increase in the conditioning temperature causes a slight increase in crystallinity degree for PLLA microspheres and clear increase in crystallization for PLA microspheres.

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Section: Thermal Properties Of Microspheresmentioning

confidence: 99%

“…Figure 7 shows a summary of the WAXD diffractograms of the PLA (A) and PLLA (B) microspheres. The course of the curves is characteristic of polylactide [26,31].…”

Section: Thermal Conductivity Of Microspheresmentioning

confidence: 99%

Section: Thermal Conductivity Of Microspheresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Influence of Thermal Annealing on Sinterability of Different Grades Polylactide Microspheres Dedicated for Laser Sintering

Gazińska¹,

Krokos²,

Kryszak³

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…Due to the crystal polymorphism of PLLA, the reorganization of conformationally disordered α′-crystals into stable α-crystals occurs on heating. In our previous paper, we precisely describe the SW determination for PLLA and composite microspheres consisted of PLLA and hydroxyapatite particles [ 27 ]. That research was focused on the influence of HAP particles on the SW range.…”

Section: Introductionmentioning

confidence: 99%

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering

et al. 2021

Self Cite

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We present a comparison of the influence of the conditioning temperature of microspheres made of medical grade poly(L-lactide) (PLLA) and polylactide with 4 wt % of D-lactide content (PLA) on the thermal and structural properties. The microspheres were fabricated using the solid-in-oil-in-water method for applications in additive manufacturing. The microspheres were annealed below the glass transition temperature (Tg), above Tg but below the onset of cold crystallization, and at two temperatures selected from the range of cold crystallization corresponding to the crystallization of the α’ and α form of poly(L-lactide), i.e., at 40, 70, 90, and 120 °C, in order to verify the influence of the conditioning temperature on the sinterability of the microspheres set as the sintering window (SW). Based on differential scanning calorimetry measurements, the SWs of the microspheres were evaluated with consideration of the existence of cold crystallization and reorganization of crystal polymorphs. The results indicated that the conditioning temperature influenced the availability and range of the SWs depending on the D-lactide presence. We postulate the need for an individual approach for polylactide powders in determining the SW as a temperature range free of any thermal events. We also characterized other core powder characteristics, such as the residual solvent content, morphology, particle size distribution, powder flowability, and thermal conductivity, as key properties for successful laser sintering. The microspheres were close to spheres, and the size of the microspheres was below 100 µm. The residual solvent content decreased with the increase of the annealing temperature. The thermal conductivities were 0.073 and 0.064 W/mK for PLA and PLLA microspheres, respectively, and this depended on the spherical shape of the microspheres. The wide angle X-ray diffraction (WAXD) studies proved that an increase in the conditioning temperature caused a slight increase in the crystallinity degree for PLLA microspheres and a clear increase in crystallization for the PLA microspheres.

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Mechanical properties and degradation of laser sintered structures of PLA microspheres obtained by dual beam laser sintering method

Kryszak

Gazińska

Gruber

et al. 2022

Int J Adv Manuf Technol

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This paper discusses the influence of process parameters on the degradation and the mechanical properties of laser-sintered polylactide (PLA) microspheres obtained using the novel dual beam laser sintering method (DBLS). DBLS is a technique developed by our team that is a modification of standard polymer laser sintering (pLS), with the potential to reduce polymer degradation during the process. The PLA microspheres were produced using the standard emulsion-solvent evaporation method. The laser sintering process was carried out in a wide range of process parameters to obtain samples with various degrees of sintering. Next a number of tests were conducted to assess the physicochemical properties of these samples, including visualization techniques (SEM, digital microscopy and photography), gel permeation chromatogrphy (GPC), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA) and static compression tests. The work shows that for different sets of process parameters, it is possible to obtain a product with similar mechanical properties, but at the same time with a completely different degree of polymer degradation. Hence, the hypothesis that when assessing the sinter quality one should take into account not only the mechanical properties of the detail, but also the degree of polymer degradation, which is of great importance, for example, in biomedical applications. It has also been shown that the DBLS method has a potential to reduce the degree of degradation of the sintered polymers and the post-process material outside the sintering zone.

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Comparison of thermal, structural and morphological properties of poly(L-lactide) and poly(L-lactide)/hydroxyapatite microspheres for laser sintering processes

Cited by 10 publications

References 22 publications

Influence of Thermal Annealing on Sinterability of Different Grades Polylactide Microspheres Dedicated for Laser Sintering

Influence of Thermal Annealing on Sinterability of Different Grades Polylactide Microspheres Dedicated for Laser Sintering

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering

Mechanical properties and degradation of laser sintered structures of PLA microspheres obtained by dual beam laser sintering method

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