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Synergistic effects of PEG middle-blocks and talcum on crystallizability and thermomechanical properties of flexible PLLA-b-PEG-b-PLLA bioplastic

  • Yaowalak Srisuwan and Yodthong Baimark EMAIL logo
Published/Copyright: April 20, 2022
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e-Polymers
From the journal e-Polymers Volume 22 Issue 1

Abstract

In this study, talcum was melt-blended with a flexible poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) triblock copolymer (PLLA-PEG-PLLA) with 1, 2, 4, and 8 wt% talcum, for improvement of the crystallization and thermomechanical properties of PLLA-PEG-PLLA compared with PLLA. The crystallizability of PLLA-PEG-PLLA/talcum composites was better than that of PLLA/talcum composites as determined from differential scanning calorimetry. X-ray diffractometry showed that the PLLA-PEG-PLLA/talcum films had a higher degree of crystallinity than the PLLA/talcum films. PEG middle-blocks and talcum showed a synergistic effect for crystallization of PLLA end-blocks. The PLLA-PEG-PLLA/talcum films showed better thermomechanical properties than those of the PLLA/talcum films as determined from dynamic mechanical analysis. This was confirmed from the results of dimensional stability to heat. In summary, the PLLA-PEG-PLLA/talcum composites have potential for use as flexible bioplastics with good dimensional stability to heat.

Keywords: poly(lactic acid); polyethylene glycol; block copolymer; talcum; nucleating agent

1 Introduction

Poly(l-lactic acid) or poly(l-lactide) (PLLA) bioplastic has attracted extensive attention for use as a replacement of traditional petroleum-based plastics to reduce plastic waste pollution. This is due to PLLA being nontoxic, biocompatible, biorenewable, biodegradable, and easily processable (1,2,3,4). Nevertheless, the drawbacks of PLLA, such as low flexibility and poor thermal resistance, because of its high glass-transition temperature (T g, approximately 60°C) and slow crystallization, have limited some applications such as hot-fill packaging, electrical devices, auto parts, and microwave applications (5,6,7).

PLLA-b-polyethylene glycol-b-PLLA triblock copolymers (PLLA-PEG-PLLA) are biocompatible and biodegradable materials that have been widely investigated for potential use in tissue engineering and drug delivery applications (8,9,10). PLLA-PEG-PLLAs have hydrophobic PLLA and hydrophilic PEG characters and are flexible bioplastics because the PEG middle-blocks induce plasticizing effects leading to a decreased T g of PLLA end-blocks (11,12,13). Moreover, the flexible PEG middle-blocks can accelerate the crystallization rate of PLLA end-blocks and increase its crystallinity (10). PLLA-PEG-PLLA has been blended with low-cost thermoplastic starch (TPS) (14). The hydrophilic PEG middle-blocks enhance good phase compatibility between PLLA-PEG-PLLA and TPS compared with PLLA/TPS blends. However, the flexible PLLA-PEG-PLLA is not sufficiently thermally resistant for use as hot-fill and microwaveable containers (15).

The thermal resistance of PLLA has been improved by increasing crystallinity and stiffness of PLLA using the addition of nucleating agents and an annealing method (6,7,16,17,18,19,20,21). Talcum is an effective nucleating agent for developing the crystallinity content of PLLA to obtain good thermal resistant PLLA (16,19,22). The combination of plasticization and nucleation effects has been extensively investigated to enhance the crystallizability of PLLA (16). The PEG/talcum combination induced faster crystallization rate and higher crystallinity content of PLLA than the PEG/clay combination (23). PEG acted as a plasticizer whereas talcum and clay acted as nucleating agents for this purpose. The PLLA with higher crystallinity content exhibited better thermal resistance. The stereocomplexation rate and homocrystallization level of PLLA/poly(d-lactic acid) blends have also been influenced by combining plasticization and nucleation of PEG/talcum mixture (24).

However, PLLA-PEG-PLLA/talcum composites have not been reported in the literature. In this study, PLLA-PEG-PLLA/talcum composites were prepared by a melt blending method. The influence of talcum content on crystallization behavior, thermomechanical properties, and mechanical properties of flexible PLLA-PEG-PLLA was investigated. The PLLA/talcum composites were also prepared for comparison.

2 Experiment

2.1 Materials

PLLA and PLLA-PEG-PLLA with number-average molecular weight (M n) of 87,600 and 88,700 g·mol−1, respectively, and dispersity (Ð) of 2.1 and 2.7, respectively, from gel permeation chromatography were used. They were synthesized by ring-opening polymerization of l-lactide monomer (96% l-enantiomer content) in bulk at 165°C for 6 h under nitrogen atmosphere using 1-dodecanol/stannous octoate and PEG (molecular weight of 20,000 g·mol−1)/stannous octoate as the initiating systems, respectively, as described in our previous works (11,12). Polymerization reaction and chemical microstructure of PLLA-PEG-PLLA from 1H-NMR spectroscopy (400 MHz NMR, Bruker Ascend) are presented in Figure 1. Talcum grade 1250 with average particle size of 10 μm was supplied by Thai Poly Chemical Co., Ltd. (Thailand).

Figure 1 (a) Ring-opening polymerization reaction of PLLA-PEG-PLLA and (b) 1H-NMR spectrum of PLLA-PEG-PLLA in CDCl3 at room temperature (peak assignments as shown).
Figure 1

(a) Ring-opening polymerization reaction of PLLA-PEG-PLLA and (b) 1H-NMR spectrum of PLLA-PEG-PLLA in CDCl3 at room temperature (peak assignments as shown).

2.2 Preparation of PLLA/talcum and PLLA-PEG-PLLA/talcum composites

PLLA/talcum and PLLA-PEG-PLLA/talcum composites were prepared by melt blending at 190°C with a rotor speed of 100 rpm for 4 min using a Rheomix batch mixer (HAAKE Polylab OS). All components were dried at 50°C under vacuum overnight before melt blending. PLLA/talcum and PLLA-PEG-PLLA/talcum composites with talcum contents of 1, 2, 4, and 8 wt% were investigated.

Composite films 100 mm × 100 mm × 0.2 mm in size were prepared by compression molding using an Auto CH Carver laboratory press at 200°C without any force for 3 min before compressing at 200°C under 10 MPa load for 1 min. The obtained films were transferred rapidly to a water-cooling plate under the same load for 1 min.

2.3 Characterization of PLLA/talcum and PLLA-PEG-PLLA/talcum composites

The thermal transition properties, glass transition (T g), cold crystallization (T cc), and melting (T m) temperatures as well as enthalpies of melting (∆H m), and cold crystallization (∆H cc) of the composites were determined using a differential scanning calorimeter (DSC, Perkin-Elmer Pyris Diamond) under nitrogen gas flow.

The thermal history of the composites was first removed by melting at 200°C for 3 min before fast quenching to 0°C. After that, the thermal transitions were recorded by scanning from 0°C to 200°C at a heating rate of 10°C·min−1. The degree of crystallinity from DSC (DSC-X c) of the PLLA phase was calculated using the following equation:

(1) DSC- X c ( % ) = [ ( Δ H m − Δ H cc ) / ( 93.7 × W PLLA ) ] × 100

where 93.7 J·g−1 is ΔH m for 100% X c PLLA (25). W PLLA is the PLLA weight-fraction of the composites calculated from PLLA fraction (PLLA = 1.00 and PLLA-PEG-PLLA = 0.83 obtained from 1H-NMR) (12) and the talcum content.

For half crystallization time (t 1/2) determination, the composites were first heated at 200°C for 3 min to completely erase their thermal history, then quenched to 120°C at a rate of 50°C·min−1 and then isothermally scanned at 120°C until the completion of crystallization (26). The t 1/2 is the time required to achieve half of the final crystallinity.

The crystalline structures of the composite films were investigated using a wide-angle X-ray diffractometer (XRD, Bruker D8 Advance) in the angle range of 2θ = 5°–30° equipped with a copper tube operating at 40 kV and 40 mA producing Cu-Kα radiation. Scan speed was 3°·min−1. The degree of crystallinity from XRD (XRD-X c) of the composite films was calculated using the following equation:

(2) XRD- X c ( % ) = ( S c / S a ) × 100

where S c and S a are the integrated intensity peaks for PLLA crystallites and the integrated intensity of the amorphous halo, respectively.

The thermomechanical properties of the composite films (6 mm × 30 mm × 0.2 mm) were determined by dynamic mechanical analysis (DMA) using a TA Instrument Q800 DMA from 30°C to 150°C at a heating rate of 2°C·min−1 under a tensile mode with the scan amplitude of 10 μm and the scanning frequency of 1 Hz.

The dimensional stability to heat of composite films was measured by hanging a sample in an 80°C oven for 30 s with a 200 g weight hanging from it. The initial length of composite films was 20 mm (15,27). The dimensional stability to heat was calculated in the following equation:

(3) Dimensional stability to heat (%) = [ Initial length (mm) / Final length (mm) ] × 100

The tensile properties of the composite films 100 mm × 10 mm in size were tested using a universal mechanical testing machine (Liyi Environmental Technology LY-1066B) with a load cell of 100 kg. A crosshead speed of 50 mm·min−1 and a gauge length of 50 mm were chosen. The averaged tensile properties were obtained from at least five determinations.

2.4 Statistical analysis

The dimensional stability to heat and tensile properties were expressed as mean and standard deviation. The statistical analysis was carried out using one-way analysis of variance (SPSS version 17.0 Institute Inc., Cary, NC) with Duncan’s multiple test (p < 0.05).

3 Results and discussion

3.1 Thermal transition properties

DSC was used to investigate thermal transition properties of the PLLA/talcum and PLLA-PEG-PLLA/talcum composites. Figure 2 shows the DSC heating curves of the composites and the results are summarized in Table 1. It can be seen that the T cc peaks of PLLA/talcum composites steadily shifted to lower temperature as the talcum content increased, suggesting that the talcum acted as heterogeneous nucleating points to enhance PLLA crystallization (28,29). The talcum with lower surface free-energy barrier enhanced nucleation and thus initiated crystallization of polymer matrices through an epitaxial mechanism (23,30). The T cc peak of pure PLLA-PEG-PLLA at 70°C was not present when the talcum was added indicating that the crystallization of PLLA-PEG-PLLA/talcum composites was complete during the quenching step in the DSC method. The T m peaks of PLLA/talcum and PLLA-PEG-PLLA/talcum composite series were in the ranges 174°C–175°C and 165°C–167°C, respectively. The T m peaks of PLLA-PEG-PLLA were at lower temperatures than those of the PLLA. This may be explained if the PEG middle-blocks of PLLA-PEG-PLLA could inhibit the thickening of PLLA end-block lamellar structures to shift T m peaks of PLLA end-blocks to lower temperature (31). The pure PLLA-PEG-PLLA (38.0%) exhibited a higher DSC-X c value than the pure PLLA (19.1%). This can be explained by the flexible PEG middle-blocks having induced a plasticizing effect leading to improved chain mobility for crystallization of PLLA end-blocks by reducing the energy required during crystallization for the chain folding process (23). The T g values of PLLA/talcum and PLLA-PEG-PLLA/talcum composites were in the ranges 59–61°C and 30–33°C, respectively.

Figure 2 DSC heating curves of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composites (a) without talcum and with talcum contents of (b) 1, (c) 2, (d) 4, and (e) 8 wt%.
Figure 2

DSC heating curves of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composites (a) without talcum and with talcum contents of (b) 1, (c) 2, (d) 4, and (e) 8 wt%.

Table 1

DSC results of PLLA/talcum and PLLA-PEG-PLLA/talcum composites

Composites Talcum (wt%) T cc (°C)a T m (°C)b DSC-X c (%)c t 1/2 at 120°C (min)d
PLLA/talcum 0 93 174 19.1 3.69
1 91 174 25.8 0.84
2 88 174 39.4 0.77
4 86 174 42.1 0.69
8 85 175 42.6 0.63
PLLA-PEG-PLLA/talcum 0 70 167 38.0 0.90
1 — 166 46.4 0.46
2 — 166 46.5 0.41
4 — 165 47.3 0.39
8 — 166 48.6 0.37

aCold crystallization temperature obtained from DSC heating curves in Figure 2; bMelting temperature obtained from DSC heating curves in Figure 2; cDegree of crystallinity from DSC calculated from Eq. 1; dHalf crystallization time obtained from relative crystallinity (X c) as a function of isothermal time in Figure 4.

The DSC-X c values of both the PLLA/talcum and PLLA-PEG-PLLA/talcum composite types significantly increased with the talcum content. The results indicated that the talcum acted as a heterogeneous nucleating agent for both the PLLA and PLLA-PEG-PLLA. The DSC-X c values of PLLA-PEG-PLLA/talcum composites were higher than those of the PLLA/talcum composites for the same talcum content. The T g values of PLLA/talcum and PLLA-PEG-PLLA/talcum composite series were in the ranges 53–56°C and 30–32°C, respectively.

Figures 3 and 4 show the DSC isothermal curves at 120°C and relative crystallinity (X c) as a function of isothermal time, respectively, of PLLA/talcum and PLLA-PEG-PLLA/talcum composites. The exothermic curves during crystallization at various talcum contents were detected. The narrower exothermic curves indicate that crystallization occurs in a shorter time (32). It is clearly seen that the exothermic curves of both PLLA and PLLA-PEG-PLLA were narrower when the talcum contents were increased. The t 1/2 values obtained from Figure 4 are also reported in Table 1. The t 1/2 of pure PLLA-PEG-PLLA (0.90 min) was shorter than the pure PLLA (3.69 min) because the plasticizing effect from flexible PEG middle-blocks to facilitated the motion of PLLA end-blocks (11,26). When 1 wt% talcum was blended, the t 1/2 values of pure PLLA and pure PLLA-PEG-PLLA substantially decreased to 0.84 and 0.46 min, respectively. The t 1/2 values of both PLLA-talcum and PLLA-PEG-PLLA/talcum composite series decreased as the talcum content increased. The PLLA-PEG-PLLA/talcum composites had shorter t 1/2 than the PLLA/talcum composites for the same talcum content. The results supported a conclusion that the talcum was an effective nucleating-agent for both the PLLA and PLLA-PEG-PLLA.

Figure 3 DSC isothermal curves at 120°C of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composites for various talcum contents.
Figure 3

DSC isothermal curves at 120°C of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composites for various talcum contents.

Figure 4 Relative crystallinity (X c) as a function of time for (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composites for various talcum contents.
Figure 4

Relative crystallinity (X c) as a function of time for (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composites for various talcum contents.

3.2 Crystalline structures

Figure 5 shows the XRD patterns of the composite films. The talcum exhibited diffraction peaks at 9° and 28° (18,29). The pure PLLA film in Figure 5 (line a) had no diffraction peaks and was assigned to being completely amorphous. For PLLA/talcum composite films, the diffraction peaks at 16.8° and 19.1° attributed to PLLA-crystalline structure (12,25) that appeared when the 1 wt% talcum was blended, and the intensities of these peaks steadily increased with the talcum content. Talcum has been extensively reported as a highly effective nucleating agent for PLLA (16). Pure PLLA-PEG-PLLA film showed a weak diffraction peak at 16.8° of PLLA crystallites. The PEG middle-blocks of PLLA-PEG-PLLA enhanced the crystallization of PLLA end-blocks by increasing their chain mobility (11,12). The intensities of diffraction peaks at 16.8° and 19.1° of the PLLA-PEG-PLLA films significantly increased with the talcum contents.

Figure 5 XRD patterns of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum films (a) without talcum and with talcum contents of (b) 1, (c) 2, (d) 4, and (e) 8 wt%.
Figure 5

XRD patterns of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum films (a) without talcum and with talcum contents of (b) 1, (c) 2, (d) 4, and (e) 8 wt%.

The XRD-X c of PLLA/talcum and PLLA-PEG-PLLA/talcum composite films significantly increased with the talcum contents as summarized in Table 2. The XRD-X c of PLLA-PEG-PLLA/talcum composite films was more than the PLLA/talcum composite films for the same talcum content. This may be explained by the flexible PEG middle-blocks and talcum addition having synergistic effects for crystallization of PLLA end-blocks of PLLA-PEG-PLLA, thereby increasing their XRD-X c. It has been reported that both the PEG and the talcum enhanced PLLA crystallization. PEG improved the chain mobility of PLLA (11,12,33), while the talcum acted as a heterogeneous nucleating agent (16,19,22).

Table 2

XRD-X c of PLLA/talcum and PLLA-PEG-PLLA/talcum films

Composite films Talcum (wt%) XRD-X c (%)a
PLLA/talcum 0 0
1 3.8
2 6.4
4 9.5
8 14.7
PLLA-PEG-PLLA/talcum 0 12.8
1 18.5
2 26.6
4 44.3
8 51.1
  1. a

    Degree of crystallinity calculated from Eq. 2.

3.3 Thermomechanical properties

DMA has been used to determine the thermomechanical properties which directly relate to the thermal resistance of PLLA (18,34,35,36,37,38). PLLA with low crystallinity content exhibited low stiffness and poor thermal resistance. The storage modulus of low crystallinity PLLA dramatically dropped as the temperature passed through the T g region before increasing again due to the cold crystallization of PLLA during the DMA heating scan. Meanwhile, high crystallinity and good thermal resistance of PLLA maintained its storage modulus and stiffness as it passed through the T g region (18,35).

Figure 6 shows the storage-modulus changes as a function of temperature of composite films. The storage moduli at 30°C of PLLA/talcum films were higher than those of the PLLA-PEG-PLLA/talcum films because the T g values of PLLA/talcum films were at higher temperature than those of PLLA-PEG-PLLA/talcum films as described by the previous DSC results. The pure PLLA and pure PLLA-PEG-PLLA films substantially decreased their storage moduli when temperature increased before increasing again, indicating that they had low stiffness and poor thermal resistance (37). The PLLA/talcum and PLLA-PEG-PLLA/talcum film series exhibited the lowest storage moduli in the range 60–100°C which significantly increased when the talcum content was increased, as summarized in Table 3. This suggests the thermal resistance of composite films increased with the talcum content. The talcum addition enhanced crystallization of composite films to increase the film crystallinity content. The crystalline region of PLLA phases maintained film stiffness at temperatures in the region of T g (23).

Figure 6 Changes of storage modulus as a function of temperature from DMA of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum films for various talcum contents.
Figure 6

Changes of storage modulus as a function of temperature from DMA of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum films for various talcum contents.

Table 3

Lowest storage modulus and dimensional stability to heat of PLLA/talcum and PLLA-PEG-PLLA/talcum films

Composite films Talcum (wt%) Lowest storage modulus in range 60–100°C (MPa) Dimensional stability to heat at 80°C (%)a
PLLA/talcum — 10 24 ± 4
1 20 31 ± 3
2 43 33 ± 5
4 58 34 ± 6
8 273 45 ± 4
PLLA-PEG-PLLA/talcum — 94 42 ± 9
1 288 81 ± 11
2 438 100
4 512 100
8 517 100
  1. a

    Calculated from Eq. 3.

It is important to note that the decreases of storage moduli of pure PLLA-PEG-PLLA and PLLA-PEG-PLLA/talcum composite films were less than those of pure PLLA and PLLA/talcum composite films. The lowest storage moduli in the range 60–100°C of PLLA-PEG-PLLA/talcum films were larger than those of the PLLA/talcum films for the same talcum content as reported in Table 3, suggesting that the PLLA-PEG-PLLA/talcum films had higher thermal resistance than the PLLA/talcum films. The results could relate to their XRD-X c values in Table 2. The higher crystallinity content of PLLA-PEG-PLLA/talcum films gave better film stiffness to maintain the storage modulus and to resist film deformation during the DMA heating scan under tension mode (20,37).

Dimensional stability to heat at 80°C under a 200 g hung load was used to determine the thermal resistance of composite films (15,27). Polypropylene film prepared by the same method in this study showed 100% dimensional stability to heat without film extension after test (data not shown). The PLLA/talcum and PLLA-PEG-PLLA/talcum films after dimensional stability to heat test are illustrated in Figure 7, and the percent dimensional stabilities to heat are reported in Table 3. The longer film-extension after test was assigned to lower thermal resistance of the films. It is seen in Table 3 that the dimensional stability to heat of the composite films increased (thermal resistance increased) with the talcum content according to the results of XRD-X c and storage modulus change (from DMA) as described above. The PLLA-PEG-PLLA/talcum films showed higher percent dimensional stabilities to heat than the PLLA/talcum films for the same talcum content.

Figure 7 Dimensional stability to heat at 80°C under 200 g load for 30 s of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum films (a) without talcum and with talcum contents of (b) 1, (c) 2, (d) 4, and (e) 8 wt%.
Figure 7

Dimensional stability to heat at 80°C under 200 g load for 30 s of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum films (a) without talcum and with talcum contents of (b) 1, (c) 2, (d) 4, and (e) 8 wt%.

It can be concluded that the PLLA-PEG-PLLA/talcum films showed better thermal resistance than the PLLA/talcum films for the same talcum content. It should be noted that the PLLA-PEG-PLLA/talcum films which contained 2, 4, and 8 wt% talcum had the same thermal resistance as the polypropylene film. Therefore, these PLLA-PEG-PLLA/talcum films can be used as high thermal resistant bioplastics.

3.4 Tensile properties

Figure 8 shows the tensile curves of the composite films. The averaged values of tensile properties are summarized in Table 4. The films of pure PLLA and PLLA/talcum composites with 1, 2, and 4 wt% talcum had tensile stress, strain at break, and Young’s modulus in the ranges 42.5–47.0 MPa, 4.3–4.5%, and 781–856 MPa, respectively. These tensile properties of PLLA composite films significantly dropped when the talcum content was increased up to 8 wt%. The film became brittle.

Figure 8 Tensile curves of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composite films for various talcum contents.
Figure 8

Tensile curves of (above) PLLA/talcum and (below) PLLA-PEG-PLLA/talcum composite films for various talcum contents.

Table 4

Averaged tensile properties of PLLA/talcum and PLLA-PEG-PLLA/talcum films

Composite films Talcum (wt%) Ultimate tensile stress (MPa) Strain at break (%) Young’s modulus (MPa)
PLLA/talcum — 47.0 ± 2.4 4.3 ± 0.3 832 ± 57
1 46.6 ± 2.2 4.3 ± 0.4 856 ± 90
2 42.7 ± 2.2 4.4 ± 0.4 829 ± 40
4 43.5 ± 2.3 4.5 ± 0.2 781 ± 81
8 22.4 ± 3.1 3.0 ± 0.2 313 ± 78
PLLA-PEG-PLLA/talcum — 13.2 ± 0.6 88.4 ± 2.9 184 ± 12
1 16.2 ± 1.8 16.2 ± 2.5 222 ± 20
2 17.7 ± 1.7 12.2 ± 1.2 261 ± 25
4 15.2 ± 1.1 8.2 ± 1.3 211 ± 14
8 15.1 ± 0.4 3.3 ± 0.2 194 ± 5

The pure PLLA-PEG-PLLA film exhibited a yield point (Figure 8, red line) suggesting that its high flexibility was due to low T g (approximately 30°C). This yield point disappeared when the talcum was blended. All the PLLA-PEG-PLLA/talcum films had higher tensile stress and Young’s moduli as well as lower strain at break than the pure PLLA-PEG-PLLA film. The tensile stress of PLLA-PEG-PLLA films increased by talcum addition suggested that talcum acted as a reinforcing filler. As the talcum contents were larger than 2 wt%, there was a decrease in tensile stress. This is because more talcum tends to agglomerate (4,39). However, the tensile stress of PLLA-PEG-PLLA/talcum films was still higher than that of the pure PLLA-PEG-PLLA film. The talcum reduced the flexibility of PLLA-PEG-PLLA film. This is due to the talcum acting as a nucleating agent to increase the XRD-X c of the composite films. The strain at break of PLLA-PEG-PLLA/talcum films steadily decreased as the talcum content increased. This may be explained by the extensibility of PLLA-PEG-PLLA films decreasing as its XRD-X c increased. The crystalline region of the flexible films resisted its extensibility. However, the PLLA-PEG-PLLA/talcum films still exhibited higher flexibility than the PLLA/talcum films for the same talcum content.

4 Conclusions

Flexible PLLA-PEG-PLLA with good thermal resistance was obtained successfully by melt blending with talcum. DSC and XRD studies indicated that the addition of talcum enhanced the crystallization of PLLA end-blocks. The addition of talcum improved the thermal resistance of both the PLLA and PLLA-PEG-PLLA composite films as revealed by the results of DMA and dimensional stability to heat. Both DSC-X c and XRD-X c values increased with increasing talcum content. The synergistic effect of plasticization from flexible PEG middle-blocks and nucleation from talcum addition induced a higher degree of crystallinity and better thermal resistance of PLLA-PEG-PLLA/talcum than the PLLA/talcum composites. The PLLA-PEG-PLLA/talcum films displayed higher flexibility as compared to PLLA/talcum composite films. Thus, the PLLA-PEG-PLLA/talcum composites could be appropriate for use as flexible bioplastics with good thermal resistance.

  1. Funding information: This research was financially supported by the Office of National Higher Education Science Research and Innovation Policy Council (NXPO), Thailand (grant no. PMU B05F630023). The authors also would like to thank the Centre of Excellence for Innovation in Chemistry (PERCH-CIC), Office of the Higher Education Commission, Ministry of Education, Thailand.

  2. Author contributions: Yaowalak Srisuwan and Yodthong Baimark planned and carried out the work. Yodthong Baimark wrote the article.

  3. Conflict of interest: Authors state no conflict of interest.

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Received: 2022-01-18
Revised: 2022-03-21
Accepted: 2022-03-27
Published Online: 2022-04-20

© 2022 Yaowalak Srisuwan and Yodthong Baimark, published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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  3. The effect of different structural designs on impact resistance to carbon fiber foam sandwich structures
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  6. Effect of polyurethane/polyvinyl alcohol coating on mechanical properties of polyester harness cord
  7. Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties
  8. Development, characterization, and in vitro evaluation of adhesive fibrous mat for mucosal propranolol delivery
  9. Fused deposition modeling of polypropylene-aluminium silicate dihydrate microcomposites
  10. Preparation of highly water-resistant wood adhesives using ECH as a crosslinking agent
  11. Chitosan-based antioxidant films incorporated with root extract of Aralia continentalis Kitagawa for active food packaging applications
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  15. Rapeseed oil gallate-amide-urethane coating material: Synthesis and evaluation of coating properties
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https://doi.org/10.1515/epoly-2022-0040
Keywords for this article
poly(lactic acid); polyethylene glycol; block copolymer; talcum; nucleating agent
Creative Commons
BY 4.0

Articles in the same Issue

  1. Research Articles
  2. The effect of isothermal crystallization on mechanical properties of poly(ethylene 2,5-furandicarboxylate)
  3. The effect of different structural designs on impact resistance to carbon fiber foam sandwich structures
  4. Hyper-crosslinked polymers with controlled multiscale porosity for effective removal of benzene from cigarette smoke
  5. The HDPE composites reinforced with waste hybrid PET/cotton fibers modified with the synthesized modifier
  6. Effect of polyurethane/polyvinyl alcohol coating on mechanical properties of polyester harness cord
  7. Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties
  8. Development, characterization, and in vitro evaluation of adhesive fibrous mat for mucosal propranolol delivery
  9. Fused deposition modeling of polypropylene-aluminium silicate dihydrate microcomposites
  10. Preparation of highly water-resistant wood adhesives using ECH as a crosslinking agent
  11. Chitosan-based antioxidant films incorporated with root extract of Aralia continentalis Kitagawa for active food packaging applications
  12. Molecular dynamics simulation of nonisothermal crystallization of a single polyethylene chain and short polyethylene chains based on OPLS force field
  13. Synthesis and properties of polyurethane acrylate oligomer based on polycaprolactone diol
  14. Preparation and electroactuation of water-based polyurethane-based polyaniline conductive composites
  15. Rapeseed oil gallate-amide-urethane coating material: Synthesis and evaluation of coating properties
  16. Synthesis and properties of tetrazole-containing polyelectrolytes based on chitosan, starch, and arabinogalactan
  17. Preparation and properties of natural rubber composite with CoFe2O4-immobilized biomass carbon
  18. A lightweight polyurethane-carbon microsphere composite foam for electromagnetic shielding
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  22. Study on the self-assembly of aromatic antimicrobial peptides based on different PAF26 peptide sequences
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  24. Experiment and analysis of mechanical properties of carbon fiber composite laminates under impact compression
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  26. A comparison study of hyaluronic acid hydrogel exquisite micropatterns with photolithography and light-cured inkjet printing methods
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  29. Preparation and applications of hydrophilic quaternary ammonium salt type polymeric antistatic agents
  30. Coefficient of thermal expansion and mechanical properties of modified fiber-reinforced boron phenolic composites
  31. Synergistic effects of PEG middle-blocks and talcum on crystallizability and thermomechanical properties of flexible PLLA-b-PEG-b-PLLA bioplastic
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  35. The role of natural rubber endogenous proteins in promoting the formation of vulcanization networks
  36. The impact of viscoelastic nanofluids on the oil droplet remobilization in porous media: An experimental approach
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  78. Review Articles
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  80. State of the art of geopolymers: A review
  81. Mechanical, thermal, and tribological characterization of bio-polymeric composites: A comprehensive review
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  83. Influence of filler material on properties of fiber-reinforced polymer composites: A review
  84. Rapid Communications
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  86. RAFT polymerization-induced self-assembly of semifluorinated liquid-crystalline block copolymers
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  93. Regenerable bacterial killing–releasing ultrathin smart hydrogel surfaces modified with zwitterionic polymer brushes
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