Influence of carbon black on the properties of plasticized poly(lactic acid) composites

doi:10.1016/j.polymdegradstab.2008.03.023

Polymer Degradation and Stability

Volume 93, Issue 6, June 2008, Pages 1044-1052

https://doi.org/10.1016/j.polymdegradstab.2008.03.023 Get rights and content

Abstract

Using acetyl tributyl citrate (ATBC) and poly(1,3-butylene adipate) (PBA) as the plasticizer of poly(lactic acid) (PLA) and carbon black (CB) as reinforced filler, high performance composites were prepared in melting blend. Fourier transform infrared spectroscopy revealed that the interaction existed between PLA and CB, and plasticizer could improve this interaction. The rheology showed that plasticizer could obviously improve the fluidity of the composites, but just the reverse for CB. Scanning electron microscopy revealed that the addition of plasticizer facilitated the dispersion of the CB in PLA. With the increasing of CB content, the enforcement effect, storage modulus and glass transition temperature increased. The elongation at break of PLA/PBA (30 wt%) could be above 600%, which was higher than the same weight ATBC plasticized PLA. Moreover, CB could restrain the thermally induced migration of plasticizer in plasticized PLA. Compared with ATBC, PBA was a thermal stable plasticizer for PLA.

Introduction

Poly(lactic acid) (PLA) is a linear aliphatic thermoplastic polyester, mainly produced by ring-opening polymerization of lactic acid, which is converted from lactic acid produced by the fermentation of annually renewable resources [1]. PLA as a high-strength, high-modulus polymer has received much attention in the research of alternative biodegradable and biocompatible polymers produced from renewable resources. This fact is responsible for a growing interest in PLA for many applications, as it is expected to reduce an impact on the environment caused by the production and utilization of petrochemical polymers [2]. Moreover with the development in polymerization technology, the price of PLA becomes more competitive. So PLA has been considered as a major alternative to petroleum-based plastics for disposable items, such as trash bags and food utensils [2].

Amorphous PLA is rigid and brittle due to the high glass transition temperature (T_g) in the range of 50–60 °C. So below this temperature, the low deformation at break limits the application of PLA materials. Therefore, considerable efforts have been made to improve the ability to plastic deformation. For example, citrate ester [3], poly(propylene glycol) (PPG) [4], triacetine, tributyl citrate [5], tributyl citrate-oligomers, diethyl bishydroxymethyl malonate-oligomers [6], oligomeric lactic acid and glycerol [7] have been used as the plasticizers to improve the flexibility of PLA. However, the addition of plasticizers generally deteriorates the precious strength and modulus of PLA. Recently, PLA/layered silicate nanocomposites exhibit remarkable improvement of mechanical, thermal, fire retardant and gas barrier at low clay content, which have received significant attentions [8], [9], [10].

Except layered silicate, nano-structured carbon fillers, such as fullerene C₆₀, single wall carbon nanotube, carbon nanohorn, carbon nanoballon and ketjenblack have been used to enhance the thermal stability of PLA material [11]. Moreover, carbon black (CB) can also improve the modulus and strength of the composite as reinforced fillers. In this paper, high performance composites are prepared with admixing small amount of CB content into plasticized PLA. At the same time, both acetyl tributyl citrate (ATBC) and poly(1,3-butylene adipate) (PBA) are used as the plasticizer for PLA. Citrate ester, ATBC has been proved to plasticize PLA effectively [3]. The ability to migrate from the plasticized material is also an important criterion to choice plasticizer. PBA is a biodegradable polymer which has been used as plasticizers in PVC-based films to enhance the leaching and migration resistance for its proper molecular weight [12], [13]. So PBA is also used as a plasticizer for PLA and PLA/CB composite to avoid its inherent brittle behavior. The influence of CB and plasticizers contents on the physical chemistry properties of composite is investigated in terms of morphology, the interaction between CB and PLA, rheology, mechanical properties, and dynamic mechanical thermal analysis (DMTA). Moreover, the thermal stability of plasticizers in plasticized PLA/CB composites is also invested in this paper.

Section snippets

Materials

Amorphous PLA was obtained from Natureworks LLC (USA). The general molecular weight average was about 1,60,000–2,20,000. The concentration of the d-(−)-isomer was 12.0 ± 1.0%. Corpren^® CB3000 was purchased from SPC, Sweden. This grade of CB had a DBP value of 380 cm³/100 g, an iodine adsorption of 1000 mg/g and a mean particle size of 40 nm, as provided by the manufacturer. PBA was purchased from Tianjin Epoch Chemistry Limited Corp. The general molecular weight average was about 1500–3000. ATBC was

FT-IR

The analysis of FT-IR spectra of the composites enabled the interactions to be identified. If there were appreciable changes (e.g. band shifts, broadening) in the FT-IR spectrum of the composites with respect to the coaddition of each component, a distinct chemical interaction (hydrogen-bonding or dipolar interaction) existed between the components [16].

On the basis of the harmonic oscillator model the reduction in force constant f could be represented by the following equation [16], [17]: $Δ f = f_{b} -$

Conclusion

In this paper, plasticized PLA/CB composites were prepared by melting blend. ATBC and PBA could improve the interaction between the PLA and CB particles, revealed by FT-IR and the dependence of tensile yield strength on the CB and plasticizer contents with the aid of Nicolais–Narkis models. Both the strong interaction (as shown in FT-IR) and the low processing viscosity (as shown in rheology) were propitious to decrease the size of CB agglomerates (as shown in SEM) when plasticizers were added

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Influence of carbon black on the properties of plasticized poly(lactic acid) composites

Abstract

Introduction

Section snippets

Materials

FT-IR

Conclusion

Prog Polym Sci

Polymer

Polym Degrad Stab

Polymer

Prog Polym Sci

Thermochim Acta

Polymer

Carbohydr Polym

An overview of polylactides as packaging materials

Macromol Biosci

Citrate esters as plasticizers for poly(lactic acid)

J Appl Polym Sci

Plasticization of poly(l-lactide) with poly(propylene glycol)

Biomacromolecules