PLA (grade 6252D especially for MB processing) was supplied by NatureWorks LLC (USA) & the flexible Thermoplastic Polyurethane (grade was purchased from BASF. Joncryl ADR 4400 used in this experiment were also purchased from BASF. All materials were used as received to produce biodegradable melt blown nonwoven without any further purification. The materials used in the experiment all were AR grade and used as received.

Melt compounding was carried out via a twin screw extruder (TSE-30A; Nanjing Ruiya Extrusion System Limited, China; length/diameter [L/D] = 40) at with a screw diameter of 18 mm And an L/D ratio of 40. Prior to melt compounding, the PLA & TPU were dried in a vacuum oven at 80˚C for 16 hours non-disturbed to eliminate the moisture. Figure 1 shows that, the PLA/TPU blend in a certain weight ratio of 95/5, 90/10, 85/15, 82/20 was melt mixed with Joncryl ADR 4400 (1% wt. % of the composites) in a mixer for 5 minutes. The melt blended extruder 7 chambers temperatures were set at 170˚C, 190˚C, 200˚C, 190˚C, 180˚C, 180˚C and 170˚C respectively.

The extruded blended samples was cooled in a clean normal water bath and then pelletized. The produced pellets were dried in a vacuum oven at 80˚C for 12 hours undisturbed and afterward stored in a vacuum at room temperature for further processes.

PLA/TPU meltblown nonwovens were prepared by using an experimental meltblown machine (Jiaxing Longman Measurement and Control Technology Co., Ltd., China). Before doing the meltblown process the blend PLA/TPU was kept in vacuum oven at 80˚C degree Celsius for 24 hours to remove the moisture. A typical meltblown spinning process and the fixed meltblown parameters in this study are shown in Figure 2. PLA/TPU MB nonwoven were manufactured by a laboratory scale MB nonwoven machine with a single orifice die. The diameter of the orifice was 0.3 mm; the L/D was 40. PLA and PLA/TPU

blends were extruded at 240˚C - 250˚C. Nitrogen gas was injected at a fixed pressure of 0.2 MPa to get a standard and uniform melt flow from the die orifice. The drawing hot air (0.3 MPa) was also kept at 270˚C - 280˚C. The spun PLA/TPU meltblown fiber were cooled at room temperature and collected on a stainless steel roller (collector) with a suction set; the collector speed and the Die to Collector Distance (DCD) were optimized according to the practical adjustment to get superior quality of meltblown nonwovens fabric.

DSC second heating and cooling curves of PLA/TPU blends are shown in Figure 3, and the corresponding thermal parameters are listed in Table 1. In the trace of PLA heating curve, the glass transition temperature (Tg) was 57.71˚C and the cold crystallization temperature (Tcc) at 111.89˚C was observed due to

the mobility and rearrangement of PLA macromolecules.

In Table 1, PLA displayed two obvious separated melting peaks (Tm) which could be explained by the mechanisms of melt recrystallization, multiple lamellae, or crystal structures. In the cooling process of PLA, no obvious crystallization peak (Tc) was found because of its slow crystallization rate.

The morphology of composites was observed by scanning electron microscopy (SEM). Figure 4 shows the SEM images of the cryofractured surface of neat polymers, non-compatibilized and compatibilized PLA/TPU blends with various weight compositions. Two important surface morphologies can be expected such as sea-island structure or matrix-droplet morphology and a co-continuous morphology when two or more immiscible polymers were melt blended together [21] [23]. SEM images (A-B-C-D-E) shows the morphological structure of the PLA/TPU 100/0, 95/5, 90/10, 85/15 and 80/20 respectively. The development of phase morphology significantly affects the properties of polymer blends and this morphological development was influenced by the different blend ratios and compositions. Adding an additive or compatibilizer can plays a vital role to make this change. All of the blends show a clear, phase-separated morphology with TPU dispersed in the PLA matrix. It can be seen in Figure 4 (image A) that 100% melt blended PLA has a smooth fractured and homogeneous surface comparatively to other blended polymer surfaces even after adding the compatibilizer. The phase morphology in binary PLA/TPU polymer blends was generally affected by the weight and viscosity ratios of blending components. It was obvious to find that PLA/TPU blends still presented a ‘‘sea-islands’’ structure as the blends images showed. TPU phases were uniformly dispersed in PLA (Poly (Lactic Acid)) matrix as globules shape roughly 8 - 9 mm in diameters, and some dispersed phases began to contact and even compress with each other when increasing the blending weight ratio of TPU. However, the interface between PLA and TPU phases in PLA/TPU/joncryl adr 4400 blends was effectively intensified in comparison to the PLA/TPU blends reported in previous studies [24]. It should be noted that some voids and de-bonding still existed, and the interface between PLA and TPU was not completely ‘‘wetted’’ by the compatibilizer, especially when the blending proportion of joncryl adr 4400 was low, i.e., PLA/TPU/joncryl adr 4400 (95/5/1). It was observed that, as the amount of TPU was increased in the composites, the

thermal stability and flexibility increased; on the other hand the brittleness of PLA reduced. The glass transition temperatures of the composites were increased with the addition of thermoplastic polyurethane and it could be attributed due to the decrease in the segmental motion of the polymer chains.

As PLA is a semicrystalline polymer, and its mechanical properties strongly depend on its crystallization behavior. Biodegradable polymers such as PLA, poly- caprolactone, polybutylene succinate, polybutylene succinate adipate, etc. are generally displayed poor thermal stability, which affected the processing and properties of end product [11]. Polymeric and composite materials properties such as thermal stability and glass transition temperature (Tg) are very important parameters for the composite materials applications. Figure 5 shows the weight as a function of temperature for PLA/TPU blends with and without compatibilizer. A single thermal degradation stage was observed in both PLA and TPU.

Figure 5 showed that, the initial thermal decomposition temperature (T_initial) of PLA was about 280.31˚C, and the practical MB processing temperature was generally < 250˚C. In comparison with PLA, TPU displayed higher thermal stability with the (T_initial) of 333.6˚C. The thermal degradation of PLA and TPU took place via different mechanisms, since two obvious decomposition stages could be observed in PLA/TPU blends. Both non-free and free radical theories were adopted to explain the thermal degradation of PLA [11] [22]. The glass transition of Poly (Lactic Acid) (PLA) is considerably affected by the addition of TPU and on the other hand glass transition of TPU phase changes very little with the addition of PLA.

To investigate the effect of TPU on the crystalline structure of PLA, the WAXD patterns of TPU with and without modification and PLA/TPU MBs were determined, as shown in Figure 6. The XRD graph shows that all the base lines of the melt blended pure PLA and PLA/TPU were nearly the same. Only two major pea k s found in the XRD graph. The main two peaks of PLA blend were found at 2θ (theta) angle of 16.64˚ and 18.94˚ which corresponds to 110 & 203 lattice plane respectively and another two peak s found at 14.75˚ & 22.31˚ which corresponds to (010) & (15) lattice plane respectively [25]. Adding TPU in the PLA there were no significant differences in the peak values, suggesting that TPU did not affect the basic structure of PLA [26].

The low crystallinity degree of Poly (Lactic Acid) (PLA) MBs could be attributed to two main reasons such as: 1) the crystallization rate of PLA was inherently low at room temperature; and the 2) PLA meltblown fibers did not have enough time to be crystallized during the rapid production process of melt blowing because it requires lower temperature to be melted [27].

The tensile mechanical properties of PLA/TPU meltblown nonwovens are shown in Figure 7. Basically the meltblown is an advanced process that can produce high quality nonwovens fabric with porous and fluffy structures (nanofiber)

fiber), consist of many superfine fibers and cohesive points which provide the mechanical strength in the fabric. When the meltblown nonwovens started stretching, generally the tensile force first makes the nonwoven fabric get narrower and gradually the fiber’s strength falls down at a n equilibrium stage. The addition of TPU at 15% and 20% could generate a noticeable improvement in the toughness of the poly (lactic acid), as figured out in the figure above in accordance with enhanced elongation at break especially, at 15 wt% content. In the above figure, it showed that PLA/TPU 85/15 linear curve 0.40 Mpa exhibits higher tensile strength compared to pure PLA or others blend. This means that with the addition of TPU, even though only 5%, the spinnability and tensile properties of the material is obviously decreased. Beside the last composite 80/20 although streng- th is higher but the durability and elongation at break point very closer to low amount of TPU added percentages. In this research it found that inappropriate amount of adding TPU or an additive resulting in poor or irregular tensile strength.

Based on the two curves above it has been seen that the viscosity is increasing gradually as the amount of TPU is increasing in the PLA blend. The rheological properties of PLA/TPU blends are investigated at 200˚C and 210˚C temperatures. Capillary Rheological Characterization melt blended at a certain shear rate dynamic apparent viscosity size. In this study, small amplitude oscillatory shear rheological experiments were conducted to compare the melt viscoelastic behaviors of the neat PLAs and the blends and to assess the compatibility between the PLA and TPU phases.

Figure 8(A) and Figure 8(B) show PLA/TPU apparent viscosity of the melt blended material shear rate increases and decreases. When the shear rate is near the 0 rad/s, at the beginning the apparent viscosity of the melt with the rise in

the mass ratio of TPU is slightly increased. Due to the TPU the viscosity of the blends increases which may be ascribed to the higher viscosity of TPU than that of PLA under the processing temperature. However, the range of blend viscosity increase is still limited. At the same time, the addition of catalyst has no obvious influence on the apparent viscosity of blends. Overall at two different temperatures are used to understand the PLA/TPU blends rheology properties. As the temperature increases the apparent viscosity of the sample has decreased. With the change in the shear rate the apparent viscosity curve substantially similar for all samples. The increasing of temperatures the shear viscosity decreased because of macromolecules chain movement enhanced so that apparent viscosity is also decreased. Increasing the rate of apparent viscosity is because of the entanglement PLA and TPU chains molecules. The entanglement between molecular chains of PLA and TPU is reduced which cause the reduction of the apparent viscosity.