Improvement of poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) film properties with nanocellulose

The improvement and investigation properties of PLLA and PLLA-PEG-PLLA were mixed nanocellulose (NC) and modified NC. 72 Table 20 Thermal transition properties of PLLA-PEG-PLLA/NC and PLLA-PEG-PLLA/modified NC composite films.

Table 19 TGA analysis of NC, modified NC, PLLA-PEG-PLLA/NC and PLLA- PLLA-PEG-PLLA/ modified NC...........................................................................................

INTRODUCTION

Background
Purpose of research
Scope of research
Expected results
Location of the study

The properties of nanocellulose exhibit low density [10], high strength [15] and high thermal property [16]. The composite films between poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) ) and nanocellulose were developed to improve their mechanical and thermal properties. To study the effect of addition of nanocellulose and modified nanocellulose on the properties of PLLA and PLLA-PEG-PLLA films in the weight ratios of 1%, 3% and 5%.

LITERATURE REVIEW

Biodegradable polymers

Type of biodegradable polymers

Polylactide

The stereoisomeric forms
The synthesis methods
The properties
Characterization of poly(L-lactide)-b-poly(ethylene glycol)-b-poly (L-

Water contact angles were measured for PLLA-PEG-PLLA triblock copolymer films with different PEG contents, as shown in Figure 10. The Tcc peaks of PLLA-PEG-PLLA were lower than those of PLLA.

Figure 3 The structures of three stereoisomeric forms, L,L-lactide, D,D-lactide, and meso-lactide [34]

Rice straw

In addition, about 29.7% of the rice residues in the field were burnt open, and about 23.2% were left in the field. Moreover, it was clear that the field with burnt rice residues had a lower tillage cost.

Figure 14 The temporal distribution of paddy reaped area in Thailand during the crop season of 2015/2016: (a) May–July 2015, (b) August–October 2015, (c) November 2015–January 2016, and (d) February–April 2016

Cellulose

Nanocellulose

Nanofibrillated cellulose
Cellulose nanocrystals
Extracted from natural cellulose fibers
Processes for nanocellulose extraction

Pretreatment extraction of nanocellulose
Alkali treatment
Acid-chlorite treatment

The properties of nanocellulose

Mechanical properties of nanocellulose
Thermal properties of nanocellulose
The crystallinity of nanocellulose

Expression of nanofibrillated cellulose (NFC) is used to express fibrils with nanometric scale sizes obtained mainly from wood through mechanochemical treatment of wood pulp. The primary fibril is 3-5 nm in diameter and approximately 500-1000 nm long, although the aggregated NFC is 20-50 nm in diameter. The acid hydrolysis method is used to eradicate the amorphous areas in the natural cellulose, and the remarkably crystalline area in natural cellulose usually remains unchanged by the acid treatment method, forming a rod-like structure, as cellulose nanocrystals (CNC) are achieved, ultimately nanocrystalline called cellulose. or cellulose whiskers as demonstrated in Figure 20.

Cellulose nanocrystal carries the wide range of properties, including large surface area, excellent stability, fascinating mechanical (higher specific strength as well as modulus), and also extraordinary optical properties. The dimension of cellulose nanocrystal is dependent on the nature of the source, and usually it possesses typical dimensions 3-30 nm in diameter as well as 100 nm to 1-2 μm in length. Cellulose nanocrystallines have been used in the role of mechanical reinforcement agents, drug delivery vehicles, templates in the synthesis of nanocomposite materials as well as protein immobilization substrate.

Nanocellulose is nothing but cellulose in the form of fibers or crystals a few micrometers long and <100 nm in diameter that can be extracted from natural cellulose fibers (Figure 21). The preliminary weight is due to the evaporation of moisture and then the thermal depolymerization of the hemicellulose and the cleavage of the glycosidic linkages of the cellulose [73]. 24 levels of crystallinity in the sequence: pineapple > banana > jute, which order is confirmed by the cellulose content values identified with these samples.

Figure 19 Various types of nanocellulose, a) cellulose fibre, b) microfirbrillated cellulose, c) nanocrystalline cellulose, d) cellulose nanofibrils [61]

Nanocellulose-based polymer composites

Thermal properties of nanocellulose-based polymer composites
Mechanical properties of nanocellulose-based polymer composites

Several authors theoretically studied the influence of nanocellulose on the mechanical properties of polymer nanocomposites. In the study, the effect of poly(ethylene glycol) (PEG) on the preparation of the poly(lactic acid) (PLA)/PEG mixture and its nanocomposites was studied by the melt intercalation method. By incorporating PEG into PLA, the tensile strength and modulus decrease, while the percentage elongation and impact strength increase predominantly. This difference was evident in the improvements in the dynamic mechanical properties of the CNC-PLA nanocomposite films.

In investigated the effect of polylactide-grafted cellulose nanocrystals on the thermal and mechanical properties of poly(l-lactide) matrices. The effect of an epoxy-based chain extender on the thermal properties, melt flow index (MFI), phase morphology and tensile properties of PLLA-PEG-PLLA was investigated and compared with PLLA homopolymer. Chain-extended PLLA-PEG-PLLA and its film were prepared by reactive melt mixing and compression molding, respectively.

The chain extension can reduce the MFI of both PLLA and PLLA-PEG-PLLA, but their crystallization abilities were suppressed. All the PLLA-PEG-PLLA films with and without chain extension had no phase separation. The results showed that the chain-extended PLLA-PEG-PLLA has potential for use as a highly flexible bioplastic.

Table 8 Thermal properties improvements for nanocellulose-based polymer composites

RESEARCH METHODOLOGY

Chemicals and instruments

Chemicals
Instruments

Experiment

Preparation of nanocellulose from rice straw
Fabrication of PLLA/nanocellulose, PLLA/modified nanocellulose,

Characterization of nanocellulose and modified nanocellulose

Particle size analyzer
Attenuated total reflectance fourier transform infrared spectrometer
Fourier transform infrared spectrometer
X-ray photoelectron spectrometer
X-Ray diffractometer
Scanning electron microscope
Transmission electron microscope
Thermogravimetric analyzer
Differential scanning calorimeter

Characterization of PLLA/nanocellulose, PLLA/modified nanocellulose,

UV-Vis spectrophotometer
Fourier transform infrared spectroscope
X-ray diffractometer
Scanning electron microscope
Differential scanning calorimeter
Thermogravimetric analyzer
Tensile testing
Water absorption

Data analysis
Abbreviation

The suspension was washed 5 times with distilled water by centrifugation (10,000 rpm, 4 ˚C, 15 min) [90, 91] to remove excess sulfuric acid. The suspension was then dialyzed against distilled water using cellulose membranes with a molecular weight of 12–14 kDa [92] until a constant pH was reached, and finally the resulting suspension was sonicated using a sonicator (at 45 ˚C, 0.5 hr.) to properly disperse suspended nanocrystals. The average particle size and size distribution of the nanocellulose and the modified nanocellulose were evaluated with a particle size analyzer in water medium. The nanocellulose and modified nanocellulose were mixed with KBr powder and then pressed into thin pellets.

The investigation of the crystallinity of the nanocellulose and modified nanocellulose was measured using X-ray diffractometer (XRD) at room temperature using CuKa radiation at 40 kV and 40 mA. The thermal properties of nanocellulose and modified nanocellulose were carried out using a thermogravimetric analyzer (TGA). Thermal properties of nanocellulose and modified nanocellulose were determined using a differential scanning calorimeter (DSC) under a nitrogen gas flow.

The nanocellulose and modified nanocellulose weighed about 3–5 mg and were kept at 200 °C for 2 min to remove thermal history. For heating DSC thermograms, the nanocellulose and modified nanocellulose were heated from −10 to 205 °C at a rate of 10 °C/min. A scanning electron microscope (SEM) was used to study the surface and morphology (shape, pattern, size) of the composite films.

Figure 25 the schematic method for modified nanocellulose [12]

RESULTS AND DISCUSSION

Characterization of nanocellulose and modified nanocellulose

Physical appearances
Attenuated total reflectance fourier transform infrared spectrometry
Fourier transform infrared spectroscopy analysis
X-ray photoelectron spectroscopy analysis
Scanning electron microscopy analysis
Transmission electron microscopy analysis
X-ray diffractometry analysis
Thermogravimetric analysis
Particle size analysis

The spectra also clearly confirmed the sequential and complete removal of lignin (1516 cm-1, aromatic skeleton vibrations) in de-lignification (Figure 27 d). The peak at 700-1250 cm-1 was assigned to Si-O or Si-O-Si [103] high intensity, by addition filled with 3-(2,3-Epoxypropoxy)propyltrimethoxysilane. The agglomeration of NC and modified NC occurred due to the large amount of intermolecular hydrogen bonds of cellulose. The XRD patterns of the bleached rice straw, NC and modified NC are shown below in Figure 32.

The crystallinity index of bleached rice straw, NC and modified NC was calculated from XRD. Bleached rice straw, NC, and modified NC showed three main characteristic peaks around 2θ values of 15.7o, 22.8o, and 34.7o, respectively, which are characteristic of cellulose crystalline structures. The degree of crystallinity of bleached rice straw, NC and modified NC is shown in Table 15.

TGA and DTG thermograms of rice straw, alkali-treated, bleached rice straw NC and modified NC are shown in Figure 33 . While NC and modified NC showed higher thermal stability than dehemicellulose(b), lignin(c) and rice straw(a) due to an increase in crystallinity and intermolecular hydrogen bonded domains after the removal of amorphous components (hemicellulose and lignin). The particle average size and distributions of NC and modified NC of two different materials are shown in Figure 34.

Figure 26 Physical appearances of rice straw (a), alkali-treated rice straw (b), bleached rice straw (c), NC (d) and modified NC (e)

Characterization of PLLA/NC and PLLA/modified NC composite films

UV-Vis spectrophotometry analysis
X-ray diffractometry analysis

Surface morphology of PLLA/NC and PLLA/modified NC
Cross-section morphology of PLLA/NC and PLLA/modified NC

Differential scanning calorimetry analysis
Tensile testing
Water absorption

The XRD analysis of pure film, PLLA/NC and PLLA/modified NC composite films were investigated for crystallinity is shown in Figure 38. While the PLLA/modified NC composite films (Figure 38 (right)) showed higher intensity than pure PLLA films. However, PLLA/modified NC composite films showed higher intensity than PLLA/NC due to interaction between PLLA and modified NC [115, 116].

PLLA/modified NC composite films were smoother and more uniform than PLLA/NC because modified NC showed less hydrophilic properties than NC [117, 118]. When comparing PLLA/NC and PLLA/modified NC, the composite films of PLLA/modified NC were shown to be smoother and more uniform than PLLA/NC. While the PLLA/modified NC composite films (c,d) showed higher thermal stability than the pure films (PLLA100).

Comparing mechanical properties of PLLA/NC and modified NC observed PLLA/modified NC higher mechanical properties than PLLA/NC. For PLLA/modified NC composite films, an increase in water absorption was observed according to modified NC content (1–5%). PLLA/NC slightly increased water absorption than PLLA/modified NC due to the hydrophilicity properties of NC.

Figure 36 Transparency of pure PLLA film, PLLA/NC and PLLA/modified NC with 210 μm thickness

Characterization of PLLA-PEG-PLLA/NC and PLLA-PEG-PLLA/modified

UV-Vis spectrophotometry analysis
X-ray diffractometer analysis

Surface morphology of PLLA-PEG-PLLA/NC and PLLA-PEG-
Cross-section morphology of PLLA-PEG-PLLA/NC and PLLA-

Differential scanning calorimeter analysis
Tensile testing
Water absorption

The optical properties of pure PLLA-PEG-PLLA film, PLLA-PEG-PLLA/NC and PLLA-PEG-PLLA/modified NC are shown in Figure 50. PLLA-PEG-PLLA/NC and PLLA-PEG-PLLA/modified NC -composite films showed slightly reduced transparency [110]. PLLA/modified NC, the PLLA-PEG-PLLA/modified NC composite films exhibited smoother and more uniform than PLLA-PEG-PLLA/NC.

The cross section of neat PLLA-PEG-PLLA film and PLLA-PEG-PLLA/NC composite films is shown in Figure 55. Adding NC (1-5% wt), the PLLA-PEG-PLLA/NC composite films showed greater irregularity and mixing then pure film. The thermal stability study of PLLA-PEG-PLLA/NC and PLLA-PEG-PLLA/modified NC composite films is shown in Figure 57.

For the modified PLLA-PEG-PLLA/NC composite films, the increase in fracture stress (29-32 MPa) and Young's modulus (535-612 MPa), followed by a reduction in elongation at break (12-15 %) compare pure PLLA-PEG -PLLA film. For PLLA-PEG-PLLA/NC composite films, water absorption increased with increasing NC content. For the modified PLLA-PEG-PLLA/NC composite films it was observed that the water absorption increased according to the modified NC content (1 -5.

Figure 49 Physical appearances of pure PLLA-PEG-PLLA film (a), PLLA-PEG- PLLA-PEG-PLLA /NC composite films in the ratios 1%wt (b), 3%wt (c) and 5%wt (d) as well as PLLA-PEG-PLLA /modified NC composite films in the ratios 1%wt (e), 3%wt

CONCLUSION

Comparing the mechanical properties of PLLA-PEG-PLLA/NC and modified NC, higher mechanical properties than PLLA-PEG-PLLA/NC were observed for modified PLLA-PEG-PLLA/NC. It can be used as reinforcing agents to increase the thermal and mechanical properties of PLLA and PLLA-PEG-PLLA. Zimmermann., "Influence of mechanical treatments on the properties of cellulose nanofibers isolated from microcrystalline cellulose," React.

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