Preparation and characterization of biodegradable polylactic acid/poly (butyleneadipate- co-terephthalate) melt-blown nonwovens for oil-water separation

doi:10.21203/rs.3.rs-3139179/v1

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Preparation and characterization of biodegradable polylactic acid/poly (butyleneadipate- co-terephthalate) melt-blown nonwovens for oil-water separation

https://doi.org/10.21203/rs.3.rs-3139179/v1

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In this work, polylactic acid/poly (butylene adipate-co-terephthalate) (PLA/PBAT) melt-blown nonwovens with well oil-water separation properties were made with melt-blown technology. The thermal, crystalline, morphology, mechanical properties, wettability, and oil-water separation performance of the PLA/PBAT melt-blown nonwovens were thoroughly investigated. The result of DSC and WAXD show that PBAT promotes the movement of the PLA molecular chain and promotes crystallinity. With increasing the blending ratio of PBAT, the ΔH_m and degree of crystallinity (X_c) of PLA were also enhanced from 38.1 to 55.1 J/g and from 1.5–15.5%, respectively, which were higher than neat PLA. Furthermore, PBAT increases the toughness and hydrophobic of the PLA melt-blown nonwovens. The elongation at break of PLA/PBAT 90/10 (53.3 ± 3.7%) was 12.3% higher than the neat PLA melt-blown nonwovens (41.0 ± 2.9%). The result of the research on the influence of the oil-water separation parameters and oil absorption experiments shows that the 90/10 PLA/PBAT melt-blown nonwoven exhibits the highest hydrophobic (water contact angle is 133.2^o). Meanwhile, the maximum adsorption efficiency of cyclohexane of nonwovens reaches 5.18 g/g. The PLA/PBAT melt-blown nonwovens have excellent oil-water separation capability.

PLA

PBAT

melt-blown nonwovens

oil-water separation

In recent decades, with the increasing amount of oil spills and industrial wastewater discharges, the environment and ecology of the earth have been seriously polluted, becoming a pressing issue worldwide. Oil-water separation is a major issue research topic in the basic science research of oily wastewater treatment and water pollution reduction. Methods such as chemical dispersants [1], in situ burning [2], and vacuum suction [3] are often used to resolve large-scale oil spills. Consequently, it is imperative to develop efficient oil-water separation technologies and materials. Compared with traditional separation methods including coagulation [4], flotation [5], centrifugation [6], magnetic separation [7], ultrasonic separation [8] and gravity separation [9], lipophilic materials with special hydrophobicity have attracted the attention of scholars. In recent decades, researchers have made great efforts to create new materials [7, 10–12]. To date, porous materials/functionalized surface structures such as foams [13, 14], sponges [15, 16], meshes [17, 18] and synthetic textile fabrics [19, 20] have received widespread attention due to their excellent oil/water separation characteristic [21]. Dong et.al used hydrophilic graphene oxide nanosheets to coat onto stainless steel meshes. To compare with neat mesh, the graphene oxide-covered mesh becomes more hydrophilic in air and super-oleophobic underwater. Using this exact opposite wettability, the graphene oxide-coated mesh uses gravity to drive the oil/water separation [22]. Yu et.al manufactured a polystyrene foam with robust magnetic that has selective absorption capabilities. The foam can absorb 17.38 times its own weight of absorption capacity and could use magnetic technology to separate from the water surface [13]. Xiong et al. used a simple and highly surface functionalization method applied to PET nonwovens to construct rod-like ZnO nanostructures. The ZnO nanostructure has roughened morphology and the amphiphilic nature of the nonwovens. The functionalized nonwoven film has hydrophobicity under water and hydrophobicity under oil [23]. Although these products show excellent oil/water separation performance, using post-treatment of these non-biodegradable products is a challenging task [21, 24, 25]. In the past two decades, there is an increasing interest in biodegradable materials for the preparation of oil/water separation products attributed to the friendly impact of renewable resources on the environment.

Today, biodegradable polylactic acid (PLA) has become a hot environmentally friendly material in the manufacturing field. Made from renewable resources, at the end of its useful life, PLA is fully biodegradable as a bio-based polymer. Lactic acid is readily available from agricultural crops [26, 27]. PLA can be degraded into water and carbon dioxide [28]. PLA has the hydrophobic ability, and researchers have conducted many studies on PLA. To impart superoleophobic and superhydrophobic properties to PLA nonwoven fabrics. Gu et al. performed a modification treatment on polydopamine (PDA)-modified PLA fabrics to improve their surface roughness. Multistage micro/nanoparticles consisting of hydrophobic polystyrene (PS) microspheres and silicon oxide (SiO₂) nanoparticles were densely deposited on the fabric. The WCA of the neat PLA nonwoven is 117 ± 3.0^o. While the mass ratio of SiO₂ nanoparticles and PS microspheres is close to 18:1, the WCA of superhydrophobic PLA nonwovens can be achieved at 152.0 ± 2.1^o [29]. Zeng et al. made a PLA nonwoven with superhydrophobic and magnetic. First, PDA was formed by polymerizing dopamine on the fabric surface to provide strong adhesion, next, in situ generated iron oxide (Fe₃O₄) particles were immobilized in situ on the PDA layer to establish surface roughness. Finally, the nonwoven was further coated with poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF) to reduce the surface energy. The WCA of PLA nonwoven was 151.7° showing superhydrophobicity [7]. Xing et al. prepared PLA/PDA/PS membranes with three-dimensional printing. The PLA/PDA/PS membrane has a petal effect. The WCA of the PLA/PDA/PS membrane is 157.1^o and exhibited low water adhesion. After 100 rounds of bending tests, PLA films exhibit excellent mechanical flexibility and maintain superhydrophobicity [30]. However, PS and poly (vinylidene fluoride-co-hexafluoropropylene) are not degradable which will cause pollution to the environment.

Poly (butylene adipate-co-terephthalate) (PBAT) is a petroleum-based but fully biodegradable aromatic-aliphatic copolymer [31], that can be prepared by poly-condensation of 1,4-butanediol with both adipic and terephthalic acids [32–34]. The processing conditions and mechanical properties are similar to polyethylene (PE) [35]. The ductility of PBAT is excellent, and the elongation at break can be 700%. Therefore, it is considered to be a good alternative to modified PLA [36, 37]. With its fully biodegradable thermoplastic, high flexibility, and good processing properties, PBAT has an excellent performance in biodegradable packaging materials and agricultural land films [38]. Li et al. used melt centrifugal spinning to prepare ultrafine PBAT/HBP fibers. In the water contact angle measurement of PBAT that could be observed that the neat PBAT fibers showed hydrophobicity with a WCA of 130.9^o ± 1.2^o, and the values were almost constant within 1.6 s [39]. Camani et al. prepared surfactant (Surfom WG 8168) modified-PBAT sheets. The water absorption test demonstrates the ability of neat PBAT to absorb water, with the neat PBAT showing a low water absorption value (~ 1%) after 350 hours, due to its hydrophobic nature [32]. Guo et al. investigated the structure and properties of soy protein isolate (SPI) and PBAT. After 24 hr of soak, 0.45% wt of its own weight of water was absorbed by the PBAT sample [40]. These studies demonstrate that PBAT is a hydrophobic polymer.

In this study, PLA/PBAT melt-blown nonwoven fibers were prepared by melt-spinning technology. The hydrophobicity of PLA was improved after the addition of PBAT, which will improve the hydrophobicity of PLA/PBAT melt-blown nonwoven. The structure and properties of PLA/PBTA melt-blown nonwoven fibers including morphology, fiber diameter, thermal, water contact angle, oil and water separation, and mechanical properties were also investigated. The performance of melt-blown nonwovens was examined by DSC, SEM, POM, WAXD, and so on. The results show that the prepared PLA/PBAT melt-blown nonwovens have promising applications in marine pollution and water harvesting.

Materials

PLA(PLA-290) was supplied by Zhejiang Haizheng Biomaterial Co. Ltd. China. The melt flow rate (MFR) is 70 g/10 min at 210 ^oC. The weight average molecular weight (M_W) is 1.26×10⁵ g/mol. PBAT was supplied by Xinjiang Blue Ridge Tunhe Polyester Co. Ltd. China. The (M_W)is 7.1×10⁴ g/mol. The MFR is 9 g/10 min at 210 ^oC.

Preparation of melt-blown nonwovens

The first step of the experiment was that PLA and PBAT were dried in a vacuum oven at 80 ^oC for 12 hours. PLA and PBAT were blended according to the different ratios of PLA/PBAT: 100/0, 98/2, 96/4, 94/6, 92/8, 90/10. The compound of PLA and PBAT blends extruded by a twin-screw extruder (Nanjing Keya Chemical Equipment Co., Ltd., length/diameter ratio (L/D ratio) was 52:1, screw diameter was 36 mm, rotating speed was 200 rpm/min), and there are thirteen heating zones. The temperature of heating zone is 100, 120, 175, 180, 180, 180, 180, 180, 180, 180,180 180, 180 ^oC, respectively. After melt blending, the PLA/PBAT blends were cooled in water, pelletized, and dried for 12 hours at 80 ^oC.

The melt-blown nonwovens equipment was produced by Foshan Nanhai Yuanjin Plastic Machinery Co., Ltd (Foshan, China). Figure 1 shows the processing of PLA/PBAT melt-blown nonwovens. The PLA/PBAT blends were melted using a single-screw extruder. The screw diameter (D) of the extruder was 55 mm and the length-diameter ratio (L/D) was 28. The temperature of heating zone is 177, 190, 190, 210, 230, 230, 230, 230 and 230 ^oC, respectively. Then, the preparation of melt-blown nonwovens was done by a melt-blown machine., the die diameter was 0.35 mm. The hot air temperature was around 250°C, and the collector distance was 10 cm. The initial polymer temperature, initial air frequency and initial air temperature are 210–230°C, 40 Hz, and 230–280 ^oC, respectively.

Differential scanning calorimetry

Thermal and crystallization behaviors of the PLA/PBAT melt-blown nonwovens were studied by differential scanning calorimetry (DSC) (TA Instruments, DSC Q20, USA). First, melt-blown nonwovens were equilibrated at 0 ^oC, and then heated at a rate of 10 ^oC/min^− 1 from 0 to 190 ^oC, and kept at 190°C for 3 min to erase the previous thermal history. Then, colded down to 0 ^oC at 10 ^oC/min. Finally, heated at a rate of 10 ^oC/min from 0 to 190 ^oC. The relative degree of crystallinity (X_c) was calculated using Eq. (1):

$${X}_{c}=\frac{\varDelta {H}_{m}-\varDelta {H}_{CC}}{\varDelta {H}_{0}\cdot C}\times 100\%$$

where ΔH₀ was the fusion enthalpy of the completely crystalline PLA, the value was taken as 93 J·g^− 1 from the literature [41], and C was the weight fraction of PLA in the blends.

Scanning electron microscopy

A scanning electron microscope (SEM) (XL-30 ESEM FEG Scanning Electron Microscope FEI COMPANY™) was used to observe the morphology of the PLA/PBAT melt-blown nonwovens under an acceleration voltage of 5 kV. All of the melt-blown nonwovens were coated with gold powder to provide enhanced conductivity.

Rheological analysis

A physical MCR 2000 rheometer (AR2000EX, TA Instruments-Waters LLC, New Castle, DE) was used to determine the rheological behavior of PLA blends. Frequency scans were performed on PLA/PBAT samples using a 25 mm plate-plate geometry under nitrogen conditions. The spacing between the parallel plates was 0.9 mm in all tests, and the thickness of the sheet samples was approximately 1.0 mm. angular frequencies used during the tests ranged from 0.1 to 100 rad/s. The temperature was plotted at 180 ^oC. The temperature of the extruder is used here, not the melt-blown temperature because the melt-blown temperature can easily degrade the PLA.

Wide-angle X-ray diffraction

Wide angle X-ray diffraction measurement was used for determining the crystalline structure of melt-blown nonwovens. WAXD was carried out with monochromatic Cu-Kα radiation (λ = 1.54A) in D8 advanced X-ray diffractometer (Bruker, Germany). The scanning range was 5–50 ^o, and the scanning rate was 5 ^o /min.

Mechanical properties of the melt-blown nonwovens

The mechanical properties of the PLA/PBAT melt-blown nonwovens were tested with a universal stretching machine (Instron-1121, Canto, MA). Cut the samples into dumbbell-shaped splines, and cut five samples from each group and with a stretch rate of 20 mm/min. At least five specimens were tested for each sample to get an average value.

Oil/water separation experiments

The WCA of the PLA/PBAT melt-blown nonwovens was measured by a contact angle measuring instrument (KRÜSS, DSA100). The volume of water droplets was controlled at 2 µl. At least five specimens were tested for each sample to get an average value.

Pour an oil/water mixture composed of 20 mL of organic solvent and 20 mL of water into the separation chamber and separated through the PLA melt-blown nonwovens filter. The separated liquid was collected in order to avoid evaporation of the solvent. To distinguish different liquids, organic solvents was treated with Sudan Red and water was dyed with anhydrous copper sulfate (CuSO₄), respectively.

During the oil sorption capacity tests, PLA/PBAT melt-blown nonwovens were immersed into 100 mL of oil in a glass beaker of 150 mL for 3min. Calculate the oil absorption capacity according to the following Eq. (2):

$$Oil absorption capacity(g/g)=\frac{{S}_{1}-{S}_{0}}{{S}_{0}}$$

where S₀ is the original weight of the sample and S₁ is the total weight of the sample with absorbed oil. In addition, to investigate the oil absorption capacity of the melt-blown nonwovens in water, cyclohexane was selected as representative of light oil and carbon tetrachloride was selected as representative of heavy oil.

DSC analysis

Table 1 DSC heating parameters of neat-PLA and PLA/PBAT melt-blown nonwovens.

Sample PLA/PBAT	T_g1 (°C)	T_cc1 (°C)	ΔH_cc1 (J/g)	T_m1 (°C)	H_m1 (J/g)	X_c1 (%)	T_c (°C)	ΔH_c (J/g)
100/0	62.1	95.0	45.2	173.9	46.7	1.5	107.8	38.1
98/2	57.1	92.1	40.9	174.3	45.3	5.0	105.9	36.5
96/4	57.7	90.0	35.8	173.0	47.2	12.6	105.3	36.8
94/6	57.9	93.8	41.1	173.1	51.1	11.3	105.7	39.1
92/8	57.3	91.0	44.6	173.2	54.8	11.9	105.7	39.3
90/10	56.4	92.2	41.3	173.3	54.3	15.5	105.3	42.2

As shown in Fig. 2, DSC results of PLA/PBAT melt-blown nonwovens, and the thermal parameters were shown in Table 1. The DSC thermograms showed the glass transition (T_g), cold-crystallization (T_cc), and melting temperature (T_m) of PLA in melt-blown nonwovens. The corresponding curves of PBAT could not be observed in thermograms due to the small content of PBAT. The first heating run was shown in Fig. 1 (a), which revealed that the T_g, T_cc and T_m of neat PLA melt-blown nonwoven was approximately 62.0°C, 95.0°C and 173.0°C. The T_g values of the PLA in PLA/PBAT nonwovens decreased with increasing PBAT content, the value of T_g decreased from 62 to 57°C. The lower T_g meant easier movement of the PLA chain segments, in other words, there was more free volume for chain segments to move [42]. The addition of PBAT decreased the T_cc by about 3°C and reduced the peak width, indicating the crystallization ability of PLA was enhanced [43]. The reason for crystallization could be carried out at a lower temperature is that PBAT promoted the migration of PLA molecular chains, and the chain mobility of the polymer segments would increase during the heating trace. With increasing the blending ratio of PBAT, the ΔH_m and X_c of PLA were also enhanced from 38.1 to 55.1 J/g and from 1.5–15.5%, respectively, which were higher than that of neat PLA. This is possible because the molecular chain movement of the PLA matrix from the molten to the crystalline state is affected by the addition of the second component. The increase in crystallinity indicates that during the melt spinning process, PLA undergoes tensile crystallization under the action of thermal and stress fields.

Figure 2 (b) demonstrated the cooling curves of melt-blown nonwovens. The ease of nucleation of polymer molecules affects the melt crystallization temperature (T_c). High T_c implied that the PLA molecules could productively crystalline at a high temperature, so the crystallization ability of the PLA in nonwovens was better than of neat PLA. The T_c of the PLA decreased from 107.8 to 105.3°C after the addition of PBAT. On the other hand, compared with neat PLA, the crystallization peak enthalpy (ΔH_c) of the PLA ingredient in the blend was broadened, indicating retarded melt crystallization of the PLA matrix.

WAXD analysis

To further investigate the influence of PBAT on the crystallization properties of PLA/PBAT melt-blown nonwovens, the crystal peaks of PLA and PBAT were analyzed by WAXD. The results were shown in Fig. 3, neat PBAT exhibited a small crystalline, the reflections of PBAT crystals were observed at 2θ = 16.3, 17.3, 20.4, 23.2 and 24.8^o [44–48], and neat PLA exhibits an amorphous [49]. In contrast, no diffraction peaks of PBAT were observed in the diffraction of all PLA / PBAT co-blend compositions. In the PLA/PBAT nonwovens, a small crystallization peak at 2θ = 16.3° was observed in the curves. The reason is that PBAT promotes the movement of the PLA molecular chain and promotes crystallization. Xiao et al. also found that PLA molecules underwent a high-speed orientation crystallization under the thermal and stress field [50].

Morphologies of neat PLA and PLA/PBAT melt-blown nonwovens

In the melt-blown processing, the molten polymer flows out from a row of much finer nozzles (holes) in the spinneret. It is quickly stretched by hot air to form fiber filaments, and then the fibers are driven by the hot air to a rotating belt collector. Figure 4 presents micrographs of PLA/PBAT melt-blown nonwovens from the observation of SEM, and the fiber diameters distribution is shown in Fig. 5. The samples produced under different components were observed, and a series of images of fabric morphology were obtained. From Fig. 4(a), it can be observed through the SEM image that neat PLA melt-blown nonwoven has a smooth surface and the fiber diameter is evenly distributed, and as shown in Fig. 5(a), the diameters of neat PLA fibers were about 7 µm. The distribution of melt-blown nonwoven fibers was attributed to the turbulent drawing airflow, which resulted in the irregular drawing force of hot air on the extruded polymer melt [51]. After PBAT was added, the surface and diameters of the melt-blown fiber changed. The diameter distribution of PLA/PBAT fibers is shown in Fig. 5 (b-f). As shown in Fig. 4(c), as the PBAT content increased to 4 wt%, fibers larger than 10 microns in diameter appeared. Due to the high melt viscosity of PBAT, the fiber diameter of PLA/PBAT melt-blown nonwovens increased. Tan et al also discovered that the increase in melt viscosity could lead to an increase in the PLA melt-blown nonwovens fiber diameter [52]. From the figures, the diameter distribution of PLA/PBAT melt-blown fibers increased and some defects in the network could be observed. Morphological changes of PLA/PBAT melt-blown nonwovens content led to the more random orientation of the fibers, as PBAT content increases from 2 wt% to 10 wt%, the mean of the fiber diameter decreased in the figure, this can be due to the large amount of PBAT particles induced by surface tension, which might break the molecular chain of fiber and accumulate on the surface.

Rheological Analysis

Rheological properties are the quantification of the relationship between the material deformation and flow of an object under the action of external forces. Rheological characterization of polymer blend systems provides insight into the compatibility of blend components and plays a key role in polymer melt-blown processing.

In this study, dynamic rheological experiments were performed on PLA / PBAT blends. PBAT could improve the elasticity of PLA and greatly enhance the melt strength of PLA. As shown in Fig. 6(a), the dynamic storage modulus (G') of PLA/PBAT blends increased with increasing PBAT content in the blends over the whole angular frequency range. Meanwhile, all PLA/PBAT blends showed higher complex viscosity |η*| value compared to neat PLA (Fig. 6b) [53], Racha et al. proved that the |η*| of PLA smaller than |η*| of PBAT at 180^oC [54]. All the PLA/PBAT blends exhibit the typical shear thinning behavior of linear polymers. The results showed that the rheological properties of PLA/PBAT blends changed with the addition of PBAT in the melt-blowing process. It was also discovered that the diameter of the melt-blown nonwoven fibers increased with increasing melt viscosity [55].

In PLA/PBAT blends, the flow behavior is more complex. The flow behavior is influenced by factors that include blending miscibility and morphology. As shown in Fig. 6(c), han plots (G'–G'') were used to investigate the miscibility of polymer blends. For all samples, the slope deviates from a value of 2 (When the mixture is considered as a genuinely even material, the slope of the Han polt in the terminal region is 2), indicating the presence of phase separation or immiscible regions in the mixture [56].

The compatibility of polymer blending systems could also be researched by the Cole-Cole plots. The smooth and semicircular shape of the plot indicates good compatibility and phase homogeneity in the molten state, and any deviation from this shape indicates inhomogeneous dispersion and phase separation attributed to immiscibility [57]. The Cole-Cole plot of neat PLA and PLA/PBAT blends was shown in Fig. 6(d), when the PBAT content was smaller than 10 wt%, there is only a circular arc on the Cole-Cole plot of the blends. When the PBAT content was 10 wt%, in the low-frequency region appeared another arc. The result has shown that the PLA/PBAT blends have definite compatibility when the PBAT content was less than 10 wt%, and phase separation happened at the PBAT content was 10 wt% [58].

Mechanical properties of neat PLA and PLA/PBAT melt-blown nonwovens

Table 2

Mechanical properties of neat PLA and PLA/PBAT melt-blown nonwovens.
Sample PLA/PBAT	Tensile stress (MPa)	Modulus (MPa)	elongation at break (%)
100/0	3.0 ± 0.3	132.0 ± 12.7	41.0 ± 2.9
98/2	2.7 ± 0.3	107.0 ± 10.9	44.5 ± 3.5
96/4	2.5 ± 0.3	96.4 ± 9.8	48.3 ± 4.0
94/6	2.5 ± 0.5	69.0 ± 6.8	47.2 ± 1.8
92/8	2.3 ± 0.5	67.2 ± 3.3	45.7 ± 2.9
90/10	2.0 ± 0.4	74.7 ± 5.4	53.3 ± 3.7

Melt-blown nonwovens have porous and fluffy structural characteristics and are composed of many bonding points and micron-level fibers, both of them supply mechanical strength for melt-blown fabrics. When the melt-blown nonwovens start to stretch, the tension will be that the fibers of melt-blown nonwovens become narrower and the fibers of the melt-blown nonwovens start to squeeze each other. When the tensile force extends to the bonding point, when it accumulates to a certain amount, the bonding point will be destroyed. Finally, the network structure of the fiber of melt-blown nonwovens is destroyed and the mechanical strength is reduced [51, 59, 60].

As shown in Table 2, it reflects the changes in the stress and strain of the melt-blown nonwovens after adding PBAT. In the stretching process, all neat PLA and PLA/PBAT melt-blown nonwovens exhibit a yielding or equilibrium phase. In the region, the competition between the orientation of fiber of PLA/PBAT melt-blown nonwovens and the disruption of bonding sites. After adding PBAT, the tensile strength and modulus of the melt-blown nonwovens decreased compared with the neat PLA melt-blown nonwovens, the reason is that PLA and PBAT are incompatible systems, which has been reported in the literature [56, 61]. This phenomenon may be due to the fact that PBAT acts as a soft elastic phase, increasing the overall flexibility. PLA exhibited higher tensile strength (3.0 ± 0.3 MPa) compared with PLA/PBAT. As PBAT content increased from 2 to 10 wt%, the tensile strength decreased from 2.7 ± 0.3 MPa to 2.0 ± 0.4 MPa. However, with the addition of PBAT, the elongation at break of PLA/PBAT melt-blown nonwovens was increased. When PBAT was added to 10 wt%, the elongation at break exceeded that of the neat PLA melt-blown nonwovens, and the elongation at break of PLA/PBAT 90/10 (53.3 ± 3.7%) was 12.3% higher than the neat PLA melt-blown nonwovens (41.0 ± 2.9%) [62]. The reason is the molecular chain of PBAT consists of a flexible segment, which has high ductility

Oil/water separation experiments

Measurement of water contact angle (WCA) is a simple and effective means of evaluating surface wettability. The hydrophobicity of the PLA/PBAT melt-blown nonwovens was tested, and the results of WCA measurements were shown in Fig. 7. The Fig. 7(a) shows that the contact angle of neat PLA melt-blown nonwovens was approximately 122.3^o. The PLA melt-blown nonwovens were hydrophobic. The addition of PBAT changes the hydrophilicity of PLA melt-blown nonwovens, the contact angle increases to 133.2^o with the addition of 10 wt% PBAT, indicating that the hydrophobicity of the PLA/PBAT melt-blown nonwovens was gradually enhanced. This shows that the addition of PBAT has promoted the hydrophobicity of PLA melt-blown nonwovens because both PLA and PBAT are hydrophobic materials. In this study, the hydrophobicity of PLA/PBAT melt-blown nonwovens is more than neat PLA melt-blown nonwovens. It can be observed by SEM that the addition of PBAT makes the fiber distribution more extensive.

To further research the application of the PLA/PBAT melt-blown nonwovens, characterization of oil-water separation performance of PLA/PBAT melt-blown nonwoven fabrics by oil-water separation test. As shown in Fig. 8 (a), the experiment of PLA/PBAT melt-blown nonwovens as the filter to separate oils and water were prepared. The melt-blown nonwovens selectively adsorb oil (dyed with Sudan red) that has been floating on the water surface for a long time. In addition, it adsorbs cyclohexane droplets dyed in water when it comes in contact with the solvent. And then the absorbed oil solvent could be easily collected simply by compressing the melt-blown nonwovens. The oil-water mixture contains dyed cyclohexane with Sudan Red and dyed water with CuSO₄. At the same time, attributed to the hydrophobic nature of the material, all water above the prepared PLA / PBAT melt-blown nonwovens was retained (Fig. 8b). There was no water observed in the collected oil, which indicates effective oil-water separation. Thus, hydrophobic/oleophilic surfaces are essentially "de-oiled", i.e. the oil penetrates the surface quickly and at the same time prevents the passage of water. Therefore, incompatible oil/water mixtures can be successfully separated [63]. The separation efficiency of the PLA melt-blown nonwoven for the oil/water mixture remained high after the 5th cycle, the result showed that the prepared PLA melt-blown nonwoven had high repeatability.

Since the adsorption capacity has a great influence on the separation performance, it is essential to evaluate it. The oil absorption capacity of the PLA and PLA/PBAT melt-blown nonwovens was tested with cyclohexane, and the corresponding results showed in Fig. 9 that the PLA and PLA/PBAT melt-blown nonwovens could absorb 4–5 times their own weight of cyclohexane. When the addition of PBAT was 4 wt%, the absorption capacity of cyclohexane reached 5.18g/g.

In general, hydrophobic materials have excellent hydrophobic properties and lipophilic properties. Cyclohexane and carbon tetrachloride were chosen as representatives of light and heavy oils to examine the oil absorption properties of melt-blown nonwovens. PLA/PBAT melt-blown nonwovens were tested for their relative adsorption capacity to cyclohexane floating on water and carbon tetrachloride submerged in water, as shown in Fig. 10. Figure 10 (a, b) shows the process of melt-blown nonwovens absorbing cyclohexane and carbon tetrachloride droplets from water, respectively. Cyclohexane and carbon tetrachloride were stained with Sudan red. Apparently, due to the difference in density, the stained cyclohexane droplets float in the upper layer of the water surface and the stained carbon tetrachloride droplets sink underwater. When the melt-blown nonwoven was exposed to two oil droplets, they were adsorbed and separated immediately from water by simple removal of the melt-blown nonwovens, with no residue observed, confirming their good selective oil absorption ability.

Different components of PLA/PBAT melt-blown nonwovens were prepared. The thermal, crystalline, mechanical, and hydrophobicity properties of the PLA/PBAT melt-blown nonwovens were researched by different analysis methods. DSC thermograms and WAXD revealed that PBAT promoted the movement of the PLA molecular chain and promotes PLA crystallinity during melt-blown nonwovens processing. After the addition of PBAT into PLA, the diameter distribution of PLA/PBAT fiber was not uniform. The reason for this might be that PLA and PBAT were incompatible systems proved by rheological analysis. However, the toughness of the melt-blown nonwovens was improved, and the elongation at break of PLA/PBAT 90/10 (53.3 ± 3.7%) was 12.3% higher than that of the neat PLA melt-blown nonwovens (41.0 ± 2.9%). The addition of PBAT also affected the hydrophilicity and oil absorption of the melt-blown nonwovens. When the addition of PBAT was 10 wt%, the nonwovens showed excellent hydrophobic with a WCA of 133.2°. Meanwhile, the maximum adsorption efficiency of cyclohexane of nonwovens reaches 5.18 g/g. Oil-water separation and adsorption behavior confirmed that the PLA/PBAT melt-blown nonwovens had excellent selective oil adsorption capacity. A high separation and adsorption efficiency of the PLA/PBAT melt-blown nonwovens was observed in our experiment. This investigation is straightforward and practical, and the degradable PLA-based hydrophobic melt-blown nonwovens has excellent potential for treating oil spills and industrial effluent discharges.

Ethics approval and consent to participate

Not applicable

Funding

This work was supported by the fund of the Chinese Academy of Sciences (Changchun Branch) (2021SYHZ0044), Science and Technology Bureau of Changchun City of China (21SH13), Development and Reform Commission of Jilin Province of China (2021C039-2), and the Science and Technology Development Plan of Jilin Province (20210203199SF).

Competing interests

No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Authors' contributions

Jinshuo Yu wrote the main manuscript text. Tao Zhao and Chentao Li prepared figures 1-5. Zhiyong Tan formal analysis. Hongwei Pan prepared figures 6-10. Huili Yang and Huiliang Zhang were in charge of funding acquisition and project administration. All authors reviewed the manuscript.

Availability of data and materials

All data and materials in this study are included in this article.

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No competing interests reported.

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Editorial decision: Major revision
05 Aug, 2023
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31 Jul, 2023
Reviewers agreed at journal
13 Jul, 2023
Reviewers agreed at journal
11 Jul, 2023
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Preparation and characterization of biodegradable polylactic acid/poly (butyleneadipate- co-terephthalate) melt-blown nonwovens for oil-water separation

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Version 1

Abstract

Figures

Introduction

Experimental

Materials

Preparation of melt-blown nonwovens

Differential scanning calorimetry

Scanning electron microscopy

Rheological analysis

Wide-angle X-ray diffraction

Mechanical properties of the melt-blown nonwovens

Oil/water separation experiments

Results and discussion

DSC analysis

WAXD analysis

Morphologies of neat PLA and PLA/PBAT melt-blown nonwovens

Rheological Analysis

Mechanical properties of neat PLA and PLA/PBAT melt-blown nonwovens

Oil/water separation experiments

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1