Cost Reduction and Mechanical Enhancement of Biopolyesters Using

Research Article pubs.acs.org/journal/ascecg

Cost Reduction and Mechanical Enhancement of Biopolyesters Using an Agricultural Byproduct from Konjac Glucomannan Processing Zhaoshu Chen,‡,∥ Lin Gan,†,∥ Peter R. Chang,§ Changhua Liu,† Jin Huang,*,† and Shanjun Gao‡ †

School of Chemistry and Chemical Engineering, Joint International Research Laboratory of Biomass-Based Macromolecular Chemistry and Materials, Southwest University, Chongqing 400715, China ‡ Department of Polymer Materials and Engineering, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, P. R. China § Bioproducts and Bioprocesses National Science Program, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada S Supporting Information *

ABSTRACT: Extensive applications of many sustainable biopolyester materials are limited due to their high cost and poor properties. To resolve these problems, we developed a strategy using an agricultural byproduct derived from konjac glucomannan processing, the konjac fly powders (KFPs), to reduce the cost, preserve the biodegradability, and improve the mechanical properties of biopolyesters. The result indicated that the multiple components in KFPs complicate our understanding of the reinforcing mechanism. However, from the tensile and dynamic mechanical behavior, matrix−filler interaction, and fracture morphology of composites, we concluded that the mechanical enhancement of KFPs was selective. By controlling melt mixing and compression molding, the elongation at break and tensile strength of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3,4)HB) rather than polybutylene succinate (PBS) or polylactide (PLA) could be enhanced by 205% and 111%, respectively, and the cost of composites reduced by 4−22%. Also, the onset degradation temperature of P(3.4)HB at a low KFP loading was about 40 °C higher than neat P(3,4)HB. The enhancing effect of KFPs was mainly attributed to its strong interaction with P(3,4)HB and the homogeneous structure of their composites. KEYWORDS: Biopolyester, Konjac fly powder, Mechanical enhancement, Cost reduction, Matrix−filler interaction

■

biopolyesters have been proposed, such as efficient catalysis,8 filler introduction,9 blending with petrochemical-derived plastics,10 and fabrication process optimization.11 Up to now, the field of biocomposites based on agricultural product fillers has probably been the best stage for biopolyesters because using those fillers usually not only reduces the cost of composites but also preserves the degradability.12 Biocomposites have been successfully prepared with fillers of avocado pulp,13 grain,14−18 cashew,19 bagasse,20 vegetable oil,21 cassava starch,22 waste gelatin,23 and soy protein.24 Unfortunately, only a few of agricultural products could be used to obtain high-performance (enhancement in mechanical properties)-modified materials directly. Konjac glucomannan

INTRODUCTION

Polymers have unquestionably been indispensable in our modern lives, from the field of materials used to make clothing, houses, and cars, to those advanced such as energy, environment, and medicine.1−3 However, the main resources of those polymers, fossil fuels, are not inexhaustible, leading to a rapidly increasing demand on renewable resources derived from polymers, “sustainable” polymers.4 Among them, biopolyesters, obtained via the fermentation of sugar5 or other methods,6 exhibit not only degradability but also considerable mechanical properties, which can be harvested in high yields from microorganisms.6,7 Although the improvements in environmental performance, together with supportive policies and legislations, have made biopolyesters applications profitable, they will still require favorable economics and higher material properties, such as mechanical strength, thermal stability, processing property, and compatibility. Many strategies to further commercialize © 2017 American Chemical Society

Received: February 27, 2017 Revised: June 14, 2017 Published: June 20, 2017 6498

DOI: 10.1021/acssuschemeng.7b00615 ACS Sustainable Chem. Eng. 2017, 5, 6498−6506

Research Article

ACS Sustainable Chemistry & Engineering

varied to be 5, 10, 15, 20, 25, and 30 parts in final composites. The fabrication of composite sheets was performed via a compressionmolding process using a hot press equipped with a water-cool system (R-3202, Wuhan Qien Science & Technology Development Co., Wuhan, China) for 10 min at 10 MPa and set temperature (160 °C for use with P(3,4)HB and PLA, 120 °C for PBS). After that, the system was water-cooled to room temperature and the pressure released. The composite series were coded as Polyester/KFP-x according to the contents of the polyester matrix and filler, where x was the theoretical KFP concentration (parts) in the composite. Also, the neat polyester samples were also prepared using the same melt compression approach. Characterization. The tensile tests were performed according to the GB/T 1040-2006 method. The tensile properties of composites, including tensile strength (the greatest stress that the material can stand without breaking, σb), elongation at break (εb), and Young’s modulus (E) were measured on a CMT6503 universal testing machine (SANSA, Shenzhen, China) with a tensile strain rate of 2.8 × 10−3 s−1 at room temperature. Composite samples were cut into a dumbbell shape with a length × width × thickness of 60 mm × 5 mm × 2 mm. The reported values reflected an average from five tests. To observe the inner microfracture of P(3,4)HB, surface morphologies of fractured samples were measured on a JSM5610LV scanning electron microscope (SEM, JEOL Ltd., Japan). Before composite morphologies were observed, the composite samples were quenched and cracked in liquid nitrogen, and then the fracture surfaces were Pt-coated in order to make them electrically conductive for observation. Differential scanning calorimetry (DSC) was performed on neat P(3,4)HB and composites (5−10 mg) via a NETZSCH DSC 214 instrument (NETZSCH Co, Selb/Bavaria, Germany) under nitrogen at a heating or cooling rate of 20 °C/min. The composite samples were scanned over a temperature range of −70−200 °C after pretreatment for eliminating the thermal history (specifically, heating from room temperature to 110 °C and then cooling to −70 °C). Thermogravimetric analysis (TGA) was performed under flowing nitrogen (30 mL/min) on a TA-STDQ600 (New Castle, USA) thermogravimetric analyzer at a heating rate of 20 °C/min. The samples (ca. 5 mg) were heated from ambient temperature to 600 °C. The dynamic mechanical analysis (DMA) of neat polyester and composites was performed on a TA Q-800 dynamic mechanical analyzer under a single cantilever mode. The tests were run in a temperature range from −60 to 110 °C for P(3,4)HB, −20 to 130 °C for PLA, and −100 to 80 °C for PBS with a heating of 5 °C/min and strain amplitude of 10 μm (strain was 0.015%) at a frequency of 1 Hz. X-ray diffraction (XRD) measurements were performed on D8 Advance X-ray diffractometer (Bruker, Germany) with Cu Kα radiation (λ = 0.154 nm) over the range of 2θ = 3−50° using a fixed time mode with a step interval of 0.02°. A DHR rotational rheometer (TA Instruments, Germany) with two parallel plates (ϕ = 25 mm) was used to investigate the rheological properties of the molten composites. The composite sample was loaded onto the bottom plate and allowed to premelt for 5 min at a given temperature (160 °C for P(3,4)HB and PLA, 120 °C for PBS). The dynamic analysis sweeping over a frequency range of 1−500 rad/s was performed to determine the dynamic properties of the composites, and the strain was controlled at 1% for the P(3,4)HB series, 10% for PBS series, and 5% for PLA series.

(KGM) is one of them, which is the main component of konjac flour and has been reported to reinforce the biopolyester.25 As a result, we believe that the byproduct from KGM processing, konjac fly powders (KFPs), of which the annual yield has exceeded 2000 t, must have great potential to mechanically enhance biopolyesters because of its high content of konjac flour (30−40 wt %). Thus, in this paper, KFPs were used for the first time as a sustainable and economical filler to reduce the cost of biopolyesters and enhance their mechanical properties via a facile melt compression-molding method. In this way, three kinds of biopolyesters, including PLA with high glass transition temperature (Tg), high melting temperature (Tm), high melt viscosity, and high crystallinity; polybutylene succinate (PBS) with low Tg and relatively low viscosity but high Tm and high crystallinity; and poly(3-hydroxybutyrate-co4-hydroxybutyrate) (P(3,4)HB) with low Tg, low Tm, low melt viscosity, and low crystallinity, were chosen as the biopolyester matrix. Then, we made a comparison among those three composites on cost and mechanical properties and studied the reinforcing effects of KFPs on different polyesters by investigating the dispersion of KFPs in polyesters, interaction between KFPs and polyesters, and thermal and rheological properties of composites. This work might contribute to finding further applications of KFPs and biopolyesters in sustainable materials and the biotechnical and fine chemical industry fields.

■

EXPERIMENTAL SECTION

Materials. Commercial poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3,4)HB) containing 5% 4HB was obtained from Tianjin Green Bioscience Corporation (Tianjin, China), with an average molecular weight (Mw) and polydispersity of 3.94 × 105 Da and 1.21, respectively. Commercial poly(butylene succinate) (PBS) with an Mw and polydispersity of 1.29 × 105 Da and 1.26, respectively, was purchased from Anqing Hexing Chemical Co., Ltd. (Anhui, China). Commercial polylactide (PLA) with an Mw and polydispersity of 8.1 × 104 Da and 1.80, respectively, was purchased from Shenzhen Esun Industrial Co., Ltd. (Shenzhen, China). KFPs with a density of 1.4 g/ cm3, were procured from Chongqing Xida Konjac Science and Technology Development Co., Ltd. (Chongqing, China). Moreover, the components of KFPs have been measured and are shown in Table 1.

Table 1. Contents of All Components but Lignocellulose in KFPs components

content (wt %)

method

starch protein konjac glucomannan ash Ca Mg Fe Zn Cu Mn

38.76 20.70 7.20 5.60 1.45 0.23 0.02 0.01 0.003 0.006

alkali solution separation Kjeldahl Method NY/T 494-2010 GB 5009.4-2006 atomic absorption spectrometry atomic absorption spectrometry atomic absorption spectrometry atomic absorption spectrometry atomic absorption spectrometry atomic absorption spectrometry

■

RESULTS AND DISCUSSION Cost Calculation of Several KFP-Filled Biopolyesters. In consideration of the low cost of KFPs (¥800/t, Table S1, ref a), it is reasonable to believe that the cost of biopolyesters will be significantly reduced by filling KFPs, as shown in Table S1. The results showed that the prices of biopolyesters, which were almost 4 times higher than those of general plastics (Table S1, ref b), had maximally decreased by 22.71%, which might make the price of KFP−biopolyester acceptable for degradable plastic

Composite Preparation. Polyesters (P(3,4)HB, PLA, PBS) and KFPs were dried at 80 °C for 24 h to wipe off the moisture content and to prevent thermal and shear degradation before use. An internal mixer (SU-70, Changzhou Suyan Science and Technology Co., Jiangsu, China) was used to prepare polyester/KFP composites by mixing at 48 rpm and set temperature (140 °C for samples with P(3,4)HB, 120 °C for PBS, 160 °C for PLA) for 10 min. The content of polyester was fixed at 100 parts in weight, and the KFP content was 6499


Research Article


filler and matrix at the interface would result in a low A, and the explanation is as follows: The mechanical loss factor tan δc of composites can be written as29,30

demanders. As a result, once the mechanical properties of the biopolyester/KFP composites were as high as or just slightly lower than those of general plastic, they would be widely utilized in vast fields. Mechanical Enhancement Studies on PLA/KFP Composites. Mechanical Properties of KFP-Filled PLA. In order to measure the mechanical properties of biopolyesters, we employed tensile tests using the GB/T 1040-2006 method and measured those of PLA first because it has been part of commercially available and able to replace petrochemically derived plastics in some types of packaging and fibers.26,27 Unfortunately, we found that not only the Young’s modulus (E) but also the elongation at break (εb) and tensile strength (σb) decreased monotonically with the loading level of KFPs (Figure 1), and all the samples were tensed to brittle fracture

tan δc = Vf tan δf + Vi tan δi + Vm tan δm

(2)

where the subscripts f, i, and m denote filler (KFPs), interphase, and matrix, respectively. Considering that the plastic deformation of reinforcing KFPs could be negligible, we assumed that tan δc ≃ 0. Also, the volume fraction of interphase Vi should be rather small. Thus, eq 2 can be rearranged to give eq 1 and tan δc ≈ (1 − Vf )(1 + A) tan δm

(3)

with A=

(Figure S1). However, there should be several components in KFPs able to reinforce PLA, such as KGM25 and starch28 (the component analysis has been completed, showing that KFPs included starch, protein, konjac glucomannan, ash, and some metal elements, and details are shown in Table 1). Thus, we believed that the key reason for the decrease in mechanical properties should be the low interaction between KFPs and PLA. Interaction between KFPs and PLA. To test the hypothesis, we analyzed the dynamic mechanical properties of PLA/KFP composites, which could be used to characterize the adhesion factor (A) between KFPs and PLA determining their interaction quantitatively. Specifically, the DMA curve of composites (storage modulus and loss factor to the temperature, shown in Figure 2a and b, respectively) was first obtained with different loading levels of KFPs and then A was calculated by eq 1, according to the methodology described by Kubat et al.29 tan δc(T ) 1 −1 1 − Vf tan δm(T )

(4)

Strong interactions between filler and matrix at the interface are beneficial to reduce the macromolecular mobility in the vicinity of the filler surface compared to that in the bulk matrix. This reduces tan δi and thus A. The DMA results and calculated A curves are shown in Figure 2c. We found that the loss factor peak of PLA was located at 60 °C and those of PLA/KFP composites were located at about 60 °C, referring to their glass-transmission temperature (Tg). Also, APLA/KFP at Tg were all above 10. Those indices were so high that the interaction between KFPs and PLA must be definitely weak because a strong one usually was related to A below 10.31,32 Unfortunately, studies on revealing the underlying reason for weak interactions between PLA and KFPs were too difficult because the components of KFPs were so complex. However, because the melt viscosity of PLA was as low as about 6 × 102 Pa s in the shear frequency range from 1 to 100 rad/s at processing temperature (measured by the DHR rotational rheometer (TA Instruments, Germany), shown in Figure S2 (Supporting Information)) and its high melting temperature (Tm, measured by DSC, shown in Figure S4a), it was hard for KFPs to disperse uniformly so that PLA/KFP composites may have a heterogeneous structure. Also, the Tg of PLA or PLA/ KFP composites was much higher than room temperature, so KFPs were still not able to permeate the free volume of PLA during the storing period. Mechanical Enhancement Studies on PBS/KFP omposites. Mechanical Properties of KFP-Filled PBS. On the basis of the above results, we chose another biopolyester, PBS, with not only a lower Tm of 107.4 °C (measured by DSC and shown in Figure S4b) but also a lower Tg (about 40 °C lower than room temperature33,34 because it has longer and more flexible hydrocarbon linear chains). As expected, first of all, the melt viscosity of PBS was lower than that of PLA (as shown in Figure S2), and then, Young’s modulus (E) increased almost monotonically with the loading level of KFPs (as shown in Figure 3a). That result suggested that compared with PLA PBS might have a stronger interaction and a lower adhesion factor (A) with KFPs (shown in Figure 3b), which was immediately confirmed by DMA (shown in Figure S3). We found APBS/KFP with different loading levels of KFPs varied just between 0 and 1.6 in the temperature range from −80 to 60 °C, which were

Figure 1. Effect of KFP content on mechanical properties of PLA/ KFP composites.

A=

Vi tan δi 1 − Vf tan δm

(1)

where tan δm(T) and tan δc(T) are the loss factors (where δ is the phase angle) of the neat matrix and composites under a specific temperature, respectively. Here, Vf is the volume fraction of KFPs. In addition, the strong interaction between 6500


Research Article


Figure 2. DMA curves (storage modulus (a) and loss factor (b) to the temperature) for neat PLA and its composites and adhesion factors (A) of PLA/KFP composites (c).

Figure 3. Effect of KFP content on mechanical properties of PBS/KFP composites (a) and adhesion factors (A) of PBS/KFP composites (b).

much lower than those of PLA/KFP composites and proved the stronger interaction between PBS and KFPs.

However, the elongation at break (εb) and tensile strength (σb) still decreased rather than increased with the loading level 6501


Research Article


g,34 ΔH*m PLA = 93.0 J/g38), respectively. Here, Wf was the weight fraction of the polyester component in the composite. Mechanical Enhancement Studies on P(3,4)HB/KFP Composites. Mechanical Properties of KFP-Filled P(3,4)HB. In order to explore if KFPs could comprehensively enhance the mechanical properties of P(3,4)HB, P(3,4)HB was mixed with KFPs on the same process and measured by tensile tests (shown in Figure 4). Finally, we found not only that the

of KFPs (as shown in Figure 3a), and all samples were tensed to brittle fracture (Figure S1). Those results indicated that even if KFPs could adhere strongly to PBS, which had a low Tg, and E of PBS had been enhanced by KFPs it was still easy for PBS/ KFP composites to form a heterogeneous structure. We supposed that the crystal of PBS might post a negative effect on the homogeneous structure of PBS/KFP composites because although the matrix chain segments of amorphous parts in those composites had been defrosted PBS had few free volumes to be permeated by KFPs when its crystallinity was high. Thus, we supposed that the crystalline of PBS might limit the mechanical enhancement. Crystallinities of Biopolyesters. On the basis of the above discussion, the crystallinities of different biopolyesters were estimated and are listed in Table 2. We found that not only in Table 2. Tg at Midpoint (Tg,mid), (Tm), Heat Enthalpy (ΔHm) of Polyester/KFP Composites and Crystallinity Degree of Polyester Component (χc) from DSC Thermograms samples

Tg mid (°C)

P(3,4)HB −6.6 P(3,4)HB-5 −2.5 P(3,4)HB-10 −2.0 P(3,4)HB-15 −2.0 P(3,4)HB-20 −2.3 P(3,4)HB-25 −2.7 P(3,4)HB-30 −2.2 samples Tg mid (°C) PBS PBS/KFP-5 PBS/KFP-10 PBS/KFP-15 PBS/KFP-20 PBS/KFP-25 PBS/KFP-30 samples PLA PLA/KFP-5 PLA/KFP-10 PLA/KFP-15 PLA/KFP-20 PLA/KFP-30

Tm1

−34.7 −31.7 −31.1 −33.8 −35.1 −35.8 −33.7 Tg mid (°C)

Tm range (°C)

ΔHm (J/g)

χc (%)

115.7156.9 116.5160.5 116.7161.2 117.4164.0 116.9159.0 117.5163.9 118.4166.1 (°C) Tm2 (°C)

35.53 30.56 34.85 29.56 28.97 29.37 29.84 ΔHm (J/g)

25.5 23.1 27.5 24.4 25.1 26.2 27.7 χc (%)

107.4 94.0 109.8 95.3 104.8 96.9 105.2 92.7 106.1 92.2 105.8 92.7 108.2 Tm (°C) ΔHm

63.3 64.6 59.3 59.0 57.8 55.1

157.7 158.6 155.8 156.5 155.0 148.1

42.41 42.80 42.02 38.33 38.58 37.60 34.01 (J/g)

39.54 38.72 42.64 41.47 41.97 45.46

Figure 4. Effect of KFP content on mechanical property of P(3,4)HB/ KFP composites.

38.45 40.74 41.91 39.96 41.97 42.61 40.80 χc (%)

Young’s modulus (E) but also the elongation at break (εb) and tensile strength (σ b) of P(3,4)HB were enhanced by introducing KFPs. Specifically, εb and σb of P(3,4)HB simultaneously reached their maximums of 16.5 MPa and 11.9% with 10 parts of KFPs, respectively, when their E increased with the loading level of KFPs on the whole. Those results indicated that εb and σb of P(3,4)HB could be enhanced by 205% and 111%, respectively, and its cost had decreased by 8.95%. Also, in the strain−stress curves of P(3,4)HB/KFP composites, yield points existed, which meant there was plastic deformation in the tensile process and the P(3,4)HB composite was no longer a brittle material via introduction of KFPs. Interaction between P(3,4)HB and KFPs. In order to further study the mechanism of the above excellent enhancement, we measured the adhesion factor (A) between P(3,4)HB and KFPs by DMA (shown in Figure 5a and b) as well. As shown in Figure 5c, AP(3,4)HB/KFP had never been above 0.2, which was lower than those of PBS and PLA. Also, extracting AP(3,4)HB/KFP data at 25 °C (shown in the Figure 5c, inset), we found AP(3,4)HB/KFP reached a minimum of −0.25 with 10 parts of KFPs. Those results indicated that P(3,4)HB, with a relatively low Tg and the lowest χc, had the strongest adhesive force to KFPs. In addition, we proved the crystalline behavior of P(3,4)HB varied little by XRD as well (shown in Figure 6); the results showed that the diffraction peaks of P(3,4)HB/KFP composites were located at the same places as those of neat P(3,4)HB. Phase Separation of P(3,4)HB/KFP Composites. In consideration of the strongest interaction between P(3,4)HB and KFPs and the lowest melt viscosity of P(3,4)HB (measured by DHR rotational rheometer and shown in Figure S2), it was

42.50 43.72 50.43 51.27 54.16 63.54

our measured data but also in the literatures35,36 the crystalline indices (χc) of PLA, PBS, and their composites with KFPs were about 40%. Those high χc probably led to the decrease in εb and σb of composites with an increase in filler content.37 Thus, we considered that P(3,4)HB, which had a low Tg of about 7 °C because of its flexible hydrocarbon chains and a relatively low χc of about 25% because of its random copolymerization structure, might be one of the best candidates for KFPenhancing biopolyesters. Here, Tm was the melting temperature of the sample measured via DSC (DSC results are shown in Figure S4); measured χc was estimated according to eq 5. χc =

ΔHm 1 × × 100% * Wf ΔHm

(5)

where ΔHm and ΔH*m were the melting enthalpy of composite and the theoretical melting enthalpy of the 100% crystalline polyester (ΔHm * P(3,4)HB = 139.3 J/g,33 ΔHm * PBS = 110.3 J/ 6502


Research Article


Figure 5. DMA curves (storage modulus (a) and loss factor (b) to the temperature) for neat P(3,4)HB and its composites and adhesion factors (A) of P(3,4)HB/KFP composites (c); the relationship between AP(3,4)HB/KFP and KFP content at 25 °C (c, inset).

entirely reasonable to believe that it was the easiest for P(3,4)HB/KFP composites to have homogeneous structures. Thus, we observed the fractured surface of neat P(3,4)HB and P(3,4)HB/KFP composites via SEM (as shown in Figure 7). The result showed that in comparison with neat P(3,4)HB (Figure 7a), the smoothness of fracture morphologies of P(3,4)HB/KFP composites decreased greatly when the loading level of KFPs was larger than 15 parts (Figure 7b−g). Specifically, in the fracture, Figure 7f (25 parts) and Figure 7g (30 parts), large particles could be observed, which means KFPs might have self-aggregated seriously when their content was too high.12 On the other hand, the fracture morphologies of P(3,4)HB/KFP-5 (Figure 7b) and P(3,4)HB/KFP-10 composites (Figure 7c) were smoother than those of other composites (Figure 7d−g). Thus, we considered that phase separation might have occurred seriously in P(3,4)HB/KFP composites when the loading level of KFPs exceeded 10 parts. Thermal Stability of P(3,4)HB/KFP Composites. Since KFPs contained at least 1.8 wt % metal ions, the thermal stability of P(3,4)HB may increase due to the strong adhesion between

Figure 6. XRD patterns of KFPs and P(3,4)HB/KFP sheets with various KFP content.

6503


Research Article


Figure 7. SEM images of fractured surface of neat P(3,4)HB (a), P(3,4)HB/KFP-5 (b), P(3,4)HB/KFP-10 (c), P(3,4)HB/KFP-15 (d), P(3,4)HB/ KFP-20 (e), P(3,4)HB/KFP-25 (f), and P(3,4)HB/KFP-30 (g).

Figure 8. Thermogravimetric and derivative thermogravimetric curves of P(3,4)HB and its composites.

KFPs and P(3,4)HB. Thus, a thermogravimetric analysis was performed for neat P(3,4)HB and its composites with KFPs to analyze their thermal degradation behavior. Figure 8 presents TGA curves (samples weight loss as the function of temperature) and shows that neat P(3,4)HB had a lower onset degradation temperature (220 °C) in comparison with P(3,4)HB/KFP composites. Also, the onset degradation temperature of P(3,4)HB/KFP composites was higher and stable with the content of KFPs (about 260 °C), as shown in Table S2, which means only a few KFPs could improve the thermal stability of P(3,4)HB significantly. Moreover, we found that the temperature of the maximum rate of decomposition of composites (285 °C) was 10 °C greater than that of the matrix (275 °C), as shown in Figure 8b. Such improvement of thermal stability could be attributed to the incorporation of KFPs into the polymer matrix. Generally, thermal stability could be improved by mixing inorganic filler with polymer matrix,39 so we believed that the thermal stability improving effect of KFPs resulted from the inorganic components in KFPs.

to prepare cost-reduced and mechanically enhanced biopolyester-based composites. The results showed that the cost of biopolyester-based composites was about 4−22% lower than that of the neat one. However, due to the weak interaction between PLA and KFPs (confirmed by the high adhesive factor (A) above 20 via DMA), the mechanical properties of PLA/ KFP composites comprehensively decreased with the loading level of KFPs. Although the components of KFPs were so complicated (including starch, protein, KGM, ash, some metal elements, and so on) that finding all components contributing to that weak interaction might be impossible, we found that high Tm (measured by DSC), high Tg (measured by DMA), and high melt viscosity of PLA imposed detrimental effects on the mechanical properties because they led to the low flexibility of PLA molecular chains and the probable difficulty for KFPs to permeate or disperse. Thus, when PLA was replaced by PBS with low Tg and relatively low Tm and melt viscosity, the Young’s modulus (E) of composites increased with the loading level of KFPs. Moreover, we proved that the interaction between PBS and KFPs was higher than that between PLA and KFPs. However, the elongation at break and tensile strength of PBS/KFP composites still decreased with the loading level of KFPs, perhaps resulting from heterogeneous structures. In consideration of the high crystalline parts in both PLA and PBS which might lead to the difficulty for permeation of fillers as well, we chose P(3,4)HB with low melt viscosity, Tg, Tm, and

■

CONCLUSION In this study, KFPs, the byproduct from KGM processing, were incorporated as a kind of sustainable and economic filler into three kinds of biopolyesters with different physicochemical properties (PLA, PBS, and P(3,4)HB) via an industrial meltcompounding and subsequent compression-molding treatment 6504


Research Article


(2) Rhim, J.-W.; Park, H.-M.; Ha, C.-S. Bio-nanocomposites for food packaging applications. Prog. Polym. Sci. 2013, 38, 1629−1652. (3) Chen, G. Q.; Patel, M. K. Plastics derived from biological sources: present and future: a technical and environmental review. Chem. Rev. 2012, 112, 2082. (4) Mohanty, A. K.; Misra, M.; Drzal, L. T. Sustainable BioComposites from Renewable Resources: Opportunities and Challenges in the Green Materials World. J. Polym. Environ. 2002, 10, 19− 26. (5) Müller, H.-M.; Seebach, D. Poly(hydroxyalkanoates): A Fifth Class of Physiologically Important Organic Biopolymers? Angew. Chem., Int. Ed. Engl. 1993, 32, 477−502; Angew. Chem., Int. Ed. Engl. 1993, 32, 477−502. (6) Reddy, C. S. K.; Ghai, R.; Rashmi; Kalia, V. C. Polyhydroxyalkanoates: an overview. Bioresour. Technol. 2003, 87, 137−46. (7) Philip, S.; Keshavarz, T.; Roy, I. Polyhydroxyalkanoates: biodegradable polymers with a range of applications. J. Chem. Technol. Biotechnol. 2007, 82, 233−247. (8) Dong, H.; Esser-Kahn, A. P.; Thakre, P. R.; Patrick, J. F.; Sottos, N. R.; White, S. R.; Moore, J. S. Chemical treatment of poly(lactic acid) fibers to enhance the rate of thermal depolymerization. ACS Appl. Mater. Interfaces 2012, 4, 503−509. (9) Rasal, R. M.; Janorkar, A. V.; Hirt, D. E. Poly(lactic acid) modifications. Prog. Polym. Sci. 2010, 35, 338−356. (10) Zhou, S. Y.; Huang, H. D.; Xu, L.; Yan, Z.; Zhong, G. J.; Hsiao, B. S.; Li, Z. M. In-situ Nanofibrillar Networks Composed of Densely Oriented Polylactide Crystals as Efficient Reinforcement and Promising Barrier Wall for Fully Biodegradable Poly(butylene succinate) Composite Films. ACS Sustainable Chem. Eng. 2016, 4, 2887−2897. (11) Ru, J.-F.; Yang, S.-G.; Zhou, D.; Yin, H.-M.; Lei, J.; Li, Z.-M. Dominant β-Form of Poly(l-lactic acid) Obtained Directly from Melt under Shear and Pressure Fields. Macromolecules 2016, 49, 3826− 3837. (12) Chen, Z.; Lin, N.; Gao, S.; Liu, C.; Huang, J.; Chang, P. R. Sustainable Composites from Biodegradable Polyester Modified with Camelina Meal: Synergistic Effects of Multicomponents on Ductility Enhancement. ACS Sustainable Chem. Eng. 2016, 4, 3228−3234. (13) Dalle Mulle Santos, C.; Pagno, C. H.; Haas Costa, T. M.; Jung Luvizetto Faccin, D.; Hickmann Flôres, S.; Medeiros Cardozo, N. S. Biobased polymer films from avocado oil extraction residue: Production and characterization. J. Appl. Polym. Sci. 2016, 133, 43957−43966. (14) Cunha, M.; Berthet, M.-A.; Pereira, R.; Covas, J. A.; Vicente, A. A.; Hilliou, L. Development of polyhydroxyalkanoate/beer spent grain fibers composites for film blowing applications. Polym. Compos. 2015, 36, 1859−1865. (15) Bledzki, A. K.; Mamun, A. A.; Volk, J. Physical, chemical and surface properties of wheat husk, rye husk and soft wood and their polypropylene composites. Composites, Part A 2010, 41, 480−488. (16) Bledzki, A. K.; Mamun, A. A.; Volk, J. Barley husk and coconut shell reinforced polypropylene composites: The effect of fibre physical, chemical and surface properties. Compos. Sci. Technol. 2010, 70, 840− 846. (17) Park, B.-D.; Wi, S. G.; Lee, K. H.; Singh, A. P.; Yoon, T.-H.; Kim, Y. S. Characterization of anatomical features and silica distribution in rice husk using microscopic and micro-analytical techniques. Biomass Bioenergy 2003, 25, 319−327. (18) Avérous, L.; Le Digabel, F. Properties of biocomposites based on lignocellulosic fillers. Carbohydr. Polym. 2006, 66, 480−493. (19) Cal, E.; Maffezzoli, A.; Mele, G.; Martina, F.; Mazzetto, S. E.; Tarzia, A.; Stifani, C. Synthesis of a novel cardanol-based benzoxazine monomer and environmentally sustainable production of polymers and bio-composites. Green Chem. 2007, 9, 754. (20) Bhattacharya, D.; Germinario, L. T.; Winter, W. T. Isolation, preparation and characterization of cellulose microfibers obtained from bagasse. Carbohydr. Polym. 2008, 73, 371−377. (21) Ruellan, A.; et al. Industrial vegetable oil by-products increase the ductility of polylactide. eXPRESS Polym. Lett. 2015, 9, 1087−1103.

crystallinity (measured by DSC) in the end. As expected, all the mechanical properties of P(3,4)HB, including E, εb, and σb, were enhanced by introducing KFPs, and the εb and σb were maximally increased by 205% and 111%, respectively. Also, the interaction between P(3,4)HB and KFPs was the strongest as the A between them was the lowest. We even observed a homogeneous structure in P(3,4)HB/KFP composites via SEM when the loading level of KFPs was below 10 parts. Moreover, the onset degradation temperature of P(3,4)HB could by improved by about 40 °C with only five parts of KFPs. We believed that those kind of high value-added composites from byproducts will be not only conducive to the further commercialization of biopolyesters but also to the comprehensive utilization of byproducts.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b00615. Specific data on the reduction of costs for polyester/KFP composites and TGA of the composites, respectively. Stress−strain curves of PLA/KFP, PBS/KFP, and P(3,4)HB/KFP composites with various KFP loading levels. Dynamic frequency sweep (complex viscosity η*) of neat PLA, PBS, and P(3,4)HB. DMA curves (storage modulus and loss factor to the temperature) for neat PBS and its composites. DSC thermograms of the PLA/KFP and PBS/KFP composites. (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*(J. Huang) E-mail: [email protected]. Tel.: +86 23 68254394. Fax: +86 23 68254394. ORCID

Zhaoshu Chen: 0000-0001-9748-8564 Jin Huang: 0000-0003-0648-2525 Author Contributions ∥

Z. Chen and L. Gan contributed equally to this work.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (51373131); Project of Basic Science and Advanced Technology Research, Chongqing Science and Technology Commission (cstc2016jcyjA0796); Project of Applied Basic Research, Wuhan Science and Technology Bureau (2015010101010015); ecoENERGY Innovation Initiative of Canada; Program of Energy Research and Development (PERD) of Canada; Key laboratory of Polymeric Composite & Functional Materials of Ministry of Education (PCFM201605); and Fundamental Research Funds for the Central Universities (WUT-2014-II-009, XDJK2016A017 and XDJK2016C033).

■

REFERENCES

(1) Reddy, M. M.; Vivekanandhan, S.; Misra, M.; Bhatia, S. K.; Mohanty, A. K. Biobased plastics and bionanocomposites: Current status and future opportunities. Prog. Polym. Sci. 2013, 38, 1653−1689. 6505


Research Article

ACS Sustainable Chemistry & Engineering (22) Teixeira, E. d. M.; Pasquini, D.; Curvelo, A. A. S.; Corradini, E.; Belgacem, M. N.; Dufresne, A. Cassava bagasse cellulose nanofibrils reinforced thermoplastic cassava starch. Carbohydr. Polym. 2009, 78, 422−431. (23) Chiellini, E.; Cinelli, P.; Corti, A.; Kenawy, E. R. Composite films based on waste gelatin: thermal−mechanical properties and biodegradation testing. Polym. Degrad. Stab. 2001, 73, 549−555. (24) Kumar, R.; Choudhary, V.; Mishra, S.; Varma, I. K.; Mattiason, B. Adhesives and plastics based on soy protein products. Ind. Crops Prod. 2002, 16, 155−172. (25) Xu, C.; Luo, X.; Lin, X.; Zhuo, X.; Liang, L. Preparation and characterization of polylactide/thermoplastic konjac glucomannan blends. Polymer 2009, 50, 3698−3705. (26) Auras, R.; Harte, B.; Selke, S. An overview of polylactides as packaging materials. Macromol. Biosci. 2004, 4, 835−864. (27) Inkinen, S.; Hakkarainen, M.; Albertsson, A. C.; Södergård, A. From lactic acid to poly(lactic acid) (PLA): characterization and analysis of PLA and its precursors. Biomacromolecules 2011, 12, 523− 32. (28) Rodrigues, C. A.; Tofanello, A.; Nantes, I. L.; Rosa, D. S. Biological Oxidative Mechanisms for Degradation of Poly(lactic acid) Blended with Thermoplastic Starch. ACS Sustainable Chem. Eng. 2015, 3, 2756−2766. (29) Kubát, J.; Rigdahl, M.; Welander, M. Characterization of interfacial interactions in high density polyethylene filled with glass spheres using dynamic-mechanical analysis. J. Appl. Polym. Sci. 1990, 39, 1527−1539. (30) Chua, P. S. Dynamic mechanical analysis studies of the interphase. Polym. Compos. 1987, 8, 308−313. (31) Muthuraj, R.; Misra, M.; Mohanty, A. K. Injection Molded Sustainable Biocomposites From Poly(butylene succinate) Bioplastic and Perennial Grass. ACS Sustainable Chem. Eng. 2015, 3, 2767−2776. (32) Wei, L.; Stark, N. M.; McDonald, A. G. Interfacial improvements in biocomposites based on poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) bioplastics reinforced and grafted with α-cellulose fibers. Green Chem. 2015, 17, 4800−4814. (33) Ding, Y.; He, J.; Yang, Y.; Cui, S.; Xu, K. Mechanical properties, thermal stability, and crystallization kinetics of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/calcium carbonate composites. Polym. Compos. 2011, 32, 1134−1142. (34) Lin, N.; Yu, J.; Chang, P. R.; Li, J.; Huang, J. Poly(butylene succinate)-based biocomposites filled with polysaccharide nanocrystals: Structure and properties. Polym. Compos. 2011, 32, 472−482. (35) Madhavan Nampoothiri, K.; Nair, N. R.; John, R. P. An overview of the recent developments in polylactide (PLA) research. Bioresour. Technol. 2010, 101, 8493−8501. (36) Xu, J.; Guo, B. H. Poly(butylene succinate) and its copolymers: Research, development and industrialization. Biotechnol. J. 2010, 5, 1149−1163. (37) Tanaka, H.; Nishi, T. New types of phase separation behavior during the crystallization process in polymer blends with phase diagram. Phys. Rev. Lett. 1985, 55, 1102−1105. (38) Zhang, Q.; Wei, S.; Huang, J.; Feng, J.; Chang, P. R. Effect of surface acetylated-chitin nanocrystals on structure and mechanical properties of poly(lactic acid). J. Appl. Polym. Sci. 2014, 131, 265−280. (39) Zhao, Y.-Q.; Lau, K.-T.; Kim, J.-k.; Xu, C.-L.; Zhao, D.-D.; Li, H.-L. Nanodiamond/poly (lactic acid) nanocomposites: Effect of nanodiamond on structure and properties of poly (lactic acid). Composites, Part B 2010, 41, 646−653.

6506


Cost Reduction and Mechanical Enhancement of Biopolyesters Using

Recommend Documents