A high heat-resistance bioplastic foam with efficient electromagnetic interference shielding
Graphical abstract
High heat-resistance poly(lactic acid) based foam with low foam density and excellent EMI shielding performance was fabricated by the nonsolvent induced phase separation and freeze-drying method.
Introduction
Conductive polymer composite (CPC) based electromagnetic interference (EMI) shielding foams are well recognized to have potential applications to dissipate and attenuate electromagnetic radiation particularly in areas such as aircraft, spacecraft and automobiles, owing to their lightweight, material saving and easy operation [1], [2], [3], [4]. The major components for CPC foams, polymer matrices, are multifarious, ranging from thermoplastics (like isotactic polypropylene (iPP) [5], polystyrene (PS) [6], and polymethylmethacrylate (PMMA) [7]) to thermosetting plastics (like phenolic [8] and polyurethane [9]). However, the present CPC foams always involve petrochemical-derived polymers, suffering from the depletion of nonrenewable petroleum. Given the sustainable development, it is necessary to develop polymer matrix for CPC foams from sustainable sources.
The current biopolymers, like poly(lactic acid) (PLA), poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and polyhydroxyalkanoate, usually exhibit relatively inferior heat resistance, hardly being used in harsh thermal environments (e.g., above 100 °C). PLA, with favorable mechanical performance and processability, is a promising bioplastic to impart improved heat resistance. This is because that stereocomplex crystallites (sc) could be formed in PLA through the stereocomplexation between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) [10]. The formation of sc with high crystallinity would endow the PLA products with outstanding heat resistance [11], [12], [13], e.g., maintaining high storage modulus even at 210 °C [11]. Unfortunately, the PLA containing 100% sc in the formed crystals, denoted as scPLA, was only fabricated in solid products and scPLA related foam products were rarely reported. One reason is that the formation of sole sc in PLA is relatively difficult, especially for PLLA and high molecular weight PDLA system [14]. Another reason is that though the formation of appropriate sc (as crystal nucleating agent) in PLA can increase its melt strength and thus benefit its foaming ability, the formation of sole sc with a relatively high crystallinity will result in excessive melt strength of PLA, which in turn suppress cell growth and spoil the foaming ability of PLA [15]. Hence, the fabrication of lightweight scPLA foams is still a great challenge.
In the current work, using carbon nanotube (CNT) as the electrically conductive material, we developed a high heat-resistance scPLA composite foam for efficient EMI shielding via a nonsolvent induced phase separation (NIPS) and freeze-drying method, as illustrated in Fig. 1. CNT was uniformly distributed in the PLLA/PDLA/dichloromethane (DCM) solution through mechanical stirring plus ultrasound. The employment of hexane could promote the intermolecular interaction between PLLA and PDLA to form sc [16], and the formed sc would act as physical crosslinks to construct a three-dimensional (3D) network-like structure, namely gelation [17], [18]. Finally, a highly porous and interconnected CNT/scPLA foam was obtained through freeze-drying. The NIPS and freeze-drying method facilitate the formation of lightweight CNT/scPLA foam with a density of 0.10 g/cm3 at 1.48 vol% (30 wt%) CNT loading, avoiding the problem existing in conventional melt foaming method, i.e., the limitation of foaming process due to the high melt viscosity at high CNT content. The CNT/scPLA foam shows a high specific electromagnetic interference shielding effectiveness (EMI SE) of 216 dB cm3/g and excellent heat resistance with linear shrinkage in diameter of only 4.3% even at 220 °C for 30 min.
Section snippets
Materials
PLLA pellets were obtained from the NatureWorks (4032D) with the weight-average molecular weight (Mw) of 2.23 × 105 g/mol and the polydispersity index (PDI) of 2.10. PDLA was kindly provided by The Changchun Institute of Applied Chemistry (CIAC) (China) with Mw of 9.5 × 104 g/mol and PDI of 1.80, according to GPC tests. The Tm values of PLLA and PDLA were 167.4 and 176.0 °C, measured with differential scanning calorimetry (DSC) at a heating rate of 10 °C/min. CNTs (NC7000) supplied by Nanocyl S.A.,
Results and discussion
We first examined whether sc was effectively formed in PLA by DSC. As shown in Fig. 2, a strong endothermic peak around 220 °C appears for all the DSC curves, which is exclusively for melting temperature of sc and indicates the successful formation of 100% sc in the formed crystals in neat scPLA and CNT/scPLA foams. In addition, an endothermic shoulder around 205 °C is observed on the left side of the melting peak of sc, which can be assigned to the melting of sc formed through the cold
Conclusions
Utilizing PLA as matrix and CNT as conductive filler, a bioplastic EMI shielding foam with high heat resistance is prepared by the NIPS and the freeze-drying method. The formation of 100% sc in the formed crystals makes the scPLA foams promising use in some thermal environments. The addition of CNT benefits the formation of 3D interconnected skeletons, resulting in lower foam density, higher electrical conductivity, better EMI shielding performance and more stable geometrical shape for the
Acknowledgements
The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China – China (Grant Nos. 51120135002, 51421061, 51473102, 51533004, and 51673134), the Innovation Team Program of Science and Technology Department of Sichuan Province (Grant No. 2014TD0002), and the China Postdoctoral Science Found (Grant Nos. 2015M572474, 2016T90848).
References (35)
- et al.
Electrical properties and electromagnetic interference shielding effectiveness of polypropylene/carbon fiber composite foams
Carbon
(2013) - et al.
Open-cell phenolic carbon foam and electromagnetic interference shielding properties
Carbon
(2016) - et al.
Stereocomplex crystallization of high-molecular-weight poly(L-lactic acid)/poly(D-lactic acid) racemic blends promoted by a selective nucleator
Polymer
(2015) - et al.
Stereocomplex formation of high-molecular-weight polylactide: a low temperature approach
Polymer
(2012) - et al.
Production of porous polylactic acid monoliths via nonsolvent induced phase separation
Polymer
(2014) - et al.
Isothermal ternary phase diagram of the polylactic acid-dichloromethane-hexane system
Polymer
(2014) - et al.
Electrical, morphological and rheological properties of carbon nanotube composites with polyethylene and poly(phenylene sulfide) by melt mixing
Chem. Eng. Sci.
(2009) - et al.
Early stage structural evolution of PLLA porous scaffolds in thermally induced phase separation process and the corresponding biodegradability and biological property
Polym. Degrad. Stabil.
(2012) - et al.
A facile preparation of highly interconnected macroporous poly(D, L-lactic acid-co-glycolic acid) (PLGA) scaffolds by liquid-liquid phase separation of a PLGA-dioxane-water ternary system
Polymer
(2003) - et al.
Polyethylene/carbon nanotube nano hybrid shish-kebab obtained by solvent evaporation and thin-film crystallization
Polymer
(2011)
Facile preparation of lightweight high-strength biodegradable polymer/multi-walled carbon nanotubes nanocomposite foams for electromagnetic interference shielding
Carbon
EMI shielding effectiveness of carbon based nanostructured polymeric materials: a comparative study
Carbon
Lightweight polypropylene/stainless-steel fiber composite foams with low percolation for efficient electromagnetic interference shielding
ACS Appl. Mater. Interfaces
Facile preparation of lightweight microcellular polyetherimide/graphene composite foams for electromagnetic interference shielding
ACS Appl. Mater. Interfaces
Lightweight, multifunctional polyetherimide/graphene@Fe3O4 composite foams for shielding of electromagnetic pollution
ACS Appl. Mater. Interfaces
Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks
Chinese J. Polym. Sci.
Novel carbon nanotube-polystyrene foam composites for electromagnetic interference shielding
Nano Tett.
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