THE INFLUENCE OF PHYSICAL MODIFICATION ON THE PROPERTIES OF PLA FILMS AS “GREEN” PACKAGING

MATERIALS

Aleksandra Mileti ć, Ivan Risti ć, Tanja Radusin, Branka Pili ć

International ConferenceEco-sustainable Food Packaging based on Polymers Nanomaterials: Can Nanotechnology Help Delivering Good Quality & Safe Food to Everyone?26-28 February, 2014., CNR, Rome, Italy

Introduction

New packaging material trends: sustainability, eco-efficiency and biodegradability.

� One of the most promising biopolymer and already the most commercialized is polylactic acid (PLA)

� It is a versatile, recyclable and compostable polymer, with high transparency, high molecular weight, good processability and water solubility resistance

� It exhibits high strength and modulus, that is combarable to polystyrene (PS)

However�The brittle nature of PLA homopolymer limits its us e in applications where

mechanical toughness is required

�Strategies for improving ductile properties of PLA :- Copolymerization- Plasticization - Blending- Reinforcement by nanofiller

Challenges for PLA

�Obtain good stiffness-toughness balance without compromising its tensile strength, transparency and biocompatibility

�How to improve elongation at the break without redu cing tensile strength?

�The aim of this study was to improve elongation at the break of PLA films and to modify tensile strength by adding plasticisers (such as castor or soy bean oil, poly(ethylene) glycol and dibutyl sebacate), silica nanoparticles and by blending with elastomer (based on styrene-butadiene polymer), keeping the existing thermal properties of neat PLA

Materials and methods

� A series of PLA films were prepared by:• Solution casting method and melt mixing in HAAKE Rheometer mixer• Using two different types of PLA: • Shenzen Esun, China AI1001 and Natureworks INGEO 2003D

� Additives:Nanoparticles SiO2 Evonik, Aerosil 200F , hydrophilic fumed silica with a specific surface area of 200 m2/g. this special grade is manufactured according to HACCP-Guidelines

� 4 types of plasticizers: Polyethilene glycol (M=400), Dibuthylsebacate (DBS) (M=314), Soybean oil (SBO)

(M=290) and Castor oil (CO) (M=930)

� Blending with:Elastomer styrene-butadiene-styrene

Characterization

�Thermal properties were determined using DSC TA instruments Q20. Analyses were done by following heat-cool-heat procedure: first, samples were heated to 170 ⁰C under heating rate of 10 ⁰C/min. After that, they were cooled to 20⁰C under heating rate of 20⁰C/min and heated again to 190⁰C under heating rate of 10⁰C/min

�Mechanical properties were tested using tensile strength machine Instron1122, at room temperature and under speed of 10 mm/min. From these measurements were collected two types of data: elongation at break, ε (%) and tensile strenght, σ (Mpa).

Results

�First series of films:• PLA (Shenzen Esun, China AI1001) + silica nanoparticles (1%, 2%,

5%, 10%)

�Second series of films:• PLA (Shenzen Esun, China AI1001) + plasticizers (PEG, DBS, SBO,

CO) (5%)

�Third series of films:• PLA (Shenzen Esun, China AI1001) + plasticizers (PEG, DBS, SBO,

CO) + silica nanoparticles (1%, 2%, 5%, 10%)

Method of preparation: solution casting in dichloromethane

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) Χ (%)PLA 45,50 114,00 26,35 147,50 29,54 3.41PLA+1%SiO2 43,00 112,00 19,16 148,00 32,93 14.24PLA+2%SiO2 44,00 120,00 19,96 151,00 36,24 17.40PLA+5%SiO2 43,00 114,00 18,24 149,50 38,87 22.04PLA+10%SiO2 44,00 96,00 11,45 147,00 151,00 41,34 31.93

Sample ɛ sr (%) σ sr (Mpa)PLA 3,2 47,23PLA + 1% SiO2 5,00 48,33PLA + 2% SiO2 8,30 48,46PLA + 5% SiO2 5,00 52,26PLA + 10% SiO2 4,80 55,84

PLA + SiO2, solution casting

Table 1. Thermal properties

Table 2. Mechanical properties

Sample ɛ sr (%) σ sr (Mpa)PLA 3,2 47,23PLA + PEG 112.20 21.75PLA + DBS 7,9 29,05PLA + SBO 15,40 24,32PLA + CO 27,20 25,88

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) χ (%)PLA 45,50 114,00 26,35 147,50 29,54 3.41PLA+PEG 43.00 0.00 15.63 147.50 45.61 32.02PLA+DBS 47.18 98.36 7.58 147.50 30.18 24.15PLA+SBO 39,50 100,00 16,48 147,00 152,00 47,42 33.05PLA+CO 41,00 100,00 19,54 148,00 41,72 23.70

Table 11. Thermal properties

Table 12. Mechanical properties

The influence of different plasticizers on properties of PLA

PLA + polyethylene glycol (PEG 400), solution casting

Table 3. Thermal propertiesSample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) ∆Hm (J/g) χ (%)PLA+PEG 43.00 0.00 15.63 147.50 45.61 32.02PLA+PEG+1%SiO2 50.00 90.00 21.41 152.00 39.73 19.57PLA+PEG+2%SiO2 39.50 95.00 12.55 151.00 32.62 21.44PLA+PEG+5%SiO2 39.50 97.00 13.70 146.00 46.02 34.53PLA+PEG+10%SiO2 47.00 93.00 20.53 147.00 45.62 26.80

Table 4. Mechanical propertiesSample ɛ sr (%) σ sr (Mpa)PLA + PEG 112.20 21.75PLA + PEG + 1% SiO2 15.33 36.12PLA + PEG + 2% SiO2 14.60 30.46PLA + PEG + 5% SiO2 69.20 23.73PLA + PEG + 10% SiO2 14.00 29.29

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) χ (%)

PLA+CO 41,00 100,00 19,54 148,00 41,72 23.70

PLA+CO+1%SiO2 35,00 95,00 28,26 142,00 148,00 35,57 7.81

PLA+CO+2%SiO2 35,00 96,00 26,78 145,00 148,00 32,88 6.52

PLA+CO+5%SiO2 47,50 102,50 39,52 142,50 147,00 37,12 7.05

PLA+CO+10%SiO2 39,00 95,00 25,15 143,00 148,00 35,09 10.61

Sample ɛ sr (%) σ sr (Mpa)PLA + CO 27,20 25,88PLA + CO + 1% SiO2 18,30 25,15PLA + CO + 2% SiO2 15,60 23,95PLA + CO + 5% SiO2 24,70 25,05PLA + CO + 10% SiO2 17,10 21,76

Table 9. Thermal properties

Table 10. Mechanical properties

PLA + castor oil (CO), solution casting

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) χ (%)PLA+soybean 39,50 100,00 16,48 147,00 152,00 47,42 33.05PLA+soybean+1%SiO2 45,00 105,00 15,89 144,50 44,71 30.80PLA+soybean+2%SiO2 45,00 106,00 26,77 146,00 42,26 16.55PLA+soybean+5%SiO2 47,00 108,00 33,13 146,00 46,04 13.08PLA+soybean+10%SiO2 52,00 109,50 20,56 146,50 41,81 22.71

Sample ɛ sr (%) σ sr (Mpa)PLA + SBO 15,40 24,32PLA + SBO + 1% SiO2 21.34 23.45PLA + SBO + 2% SiO2 103,70 20,72PLA + SBO + 5% SiO2 80.00 19.36PLA + SBO + 10% SiO2 74,00 17,60

Table 7. Thermal properties

Table 8. Mechanical properties

PLA + soybean oil (SBO), solution casting

Sample ɛ sr (%) σ sr (Mpa)PLA + DBS 7,9 29,05PLA + DBS + 1% SiO2 14,2 26,77PLA + DBS + 2% SiO2 8,2 37,48PLA + DBS + 5% SiO2 14,2 35,80PLA + DBS + 10% SiO2 4,1 38,50

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) χ (%)PLA+DBS 47,18 98.36 7.58 147.50 30.18 24.14PLA+DBS+1%SiO2 35,73 107,46 22,18 140,91 147,98 24,09 2.04PLA+DBS+2%SiO2 43,53 117,60 12,74 148,30 19,63 7.36PLA+DBS+5%SiO2 42,30 110,65 18,75 142,40 148,58 22,64 4.15PLA+DBS+10%SiO2 45,52 111,08 16,99 148,15 20,99 4.27

Table 5. Thermal properties

Table 6. Mechanical properties

PLA + dibutyl sebacate (DBS), solution casting

Results

Fourth series of films:• PLA (Natureworks INGEO 2003D) + silica nanoparticles (2%, 5%,

10%)Method of preparation: solution casting in dichlormethane

Fifth series of films: • PLA (Natureworks INGEO 2003D) + silica nanoparticles (2%, 5%,

10%)Method of preparation: melting

Sixth series of films: • PLA (Natureworks INGEO 2003D) + 2%, 5%, 10% elastomerMethod of preparation: melting

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) ∆Hm (J/g) χ (%)PLA 2003D 46,00 0,00 0,00 150,00 44,94 48,01PLA 2003D+2%SiO2 55,00 0,00 0,00 150,00 52,48 56,07PLA 2003D+5%SiO2 42,50 0,00 0,00 138,50 27,51 29,58PLA 2003D+10%SiO2 55,00 0,00 0,00 156,00 39,58 42,29

Sample ɛsr (%) σ sr (Mpa)PLA 2003D 26,20 143,85PLA 2003D+2%SiO2 162,00 100,00PLA 2003D+5%SiO2 148,30 96,57PLA 2003D+10%SiO2 100,30 89,99

PLA 2003D + SiO2, solution casting

Table 13. Thermal properties

Table 14. Mechanical properties

PLA 2003D + SiO2, melt

Sample ɛsr (%) σ sr (Mpa)PLA 2003D 8,50 35,48PLA 2003D+1%SiO2 116,30 24,81PLA 2003D+2%SiO2 37,40 27,95PLA 2003D+5%SiO2 14,40 31,58

Table 15. Thermal properties

Table 16. Mechanical properties

Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) χ (%)PLA 2003D 57.55 111.98 23.17 148.51 153.68 23.37 0.25PLA 2003D+1%SiO2

57.44 108.13 17.17 148.68 154.16 22.18 5.35PLA 2003D+2%SiO2

58.18 111.96 24.76 148.57 153.36 28.96 4,50PLA 2003D+5%SiO2

58 113.93 26.85 149.32 153.93 27.77 0.98

PLA 2003D + elastomer, melt

Sample ɛsr (%) σ sr (Mpa)PLA 2003D 8,50 35,48PLA 2003D+2%elastomer 125.10 13.90PLA 2003D+5%elastomer 95.80 10.66PLA 2003D+10%elastomer 32.70 7.45

Table 17. Thermal properties

Table 18. Mechanical properties

Sample Tg (⁰C) Tc (⁰C) ∆Hc (J/g) Tm1 (⁰C) Tm2 (⁰C) ∆Hm (J/g) χ (%)PLA 2003D 57.55 111.98 23.13 148.51 153.68 23.37 0.25PLA 2003D + 2% elastomer 58.89 111.51 9.77 153.87 23.68 14.86PLA 2003D + 5% elastomer 57.92 112.3 21.27 149.76 154.7 28.51 7.73PLA 2003D + 10% elastomer 57.55 111.36 18.04 149 154.5 22.62 4.85

Summary

• With the addition of plasticizers and silica nanopartilces the existing thermal properties of neat PLA are preserved, which is crucial for the application

• The addition of silica nanoparticles acts as nucleation agents, increases the degree of crystallinity and also influences the improvement of elongation at the break and tensile strength

• The addition of plasticizers improves elongation at the break, but significantly reduces tensile strength

•Adding the combination of plasticizers and silica nanoparticles in PLA, enables the modification of elongation at the break and tensile strength, but further investigation is necessary.

•Blending PLA with elastomer (SBS) increases elongation at the break and elasticity but decreases tensile strength,

I want to thank my colleagues:

Dr Ivan RistićTanja Radusin, dipl.eng.

Aleksandra Miletić, dipl.eng.

And Financial support:

Ministry of Education and Science of the Republic of Serbia, contract grant number 45022

Thank you for your attention

Novi Sad