In this article, a kind of degradable composite was prepared from bamboo fiber (BF), poly lactic acid (PLA), and polypropylene (PP). The mechanical and thermal properties were characterized by the universal testing machine, thermogravimetric analysis, differential scanning calorimetry. In order to improve the compability between BF and polymer matrix several modification on the surface of BF were explored and compared. Moreover, a compatibilizer (maleated PP) was applied to further increase compatibility between the fiber and matrix. It is found that the thermal stability of BF/PP/PLA composites decreased with the increase of maleated polypropylene (MAPP) content. When 5% MAPP was used the tensile strength, flexural strength, and impact strength of composites reached 33.73, 47.18 MPa, and 3.15 KJ/m2, with an increase by 13, 11.7, and 23.5%, respectively, compared with the composites without MAPP. The improvement of mechanical properties is attributed to the fact that irregular grooves and cracks induced by the modification of BF facilitate the infiltration of polymer into fiber due to the strong capillary effect. Furthermore, BF/PP/PLA composites are potential to be used in 3D printing. POLYM. ENG. SCI., 59:E247–E260, 2019. © 2018 Society of Plastics Engineers

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The phase behavior of binary blends of a long symmetric AB diblock copolymer and a short asymmetric AB diblock copolymer is studied using the self-consistent mean-field theory. The investigation focuses on blends with different short diblocks by constructing phase diagrams over the whole blending compositions and a large segregation regime. The influences of the chain length ratio (R) of the long and short diblock copolymers on their miscibility and on the stability of various ordered structures are explored. The theoretical results reveal that the blends have a much more complex phase behavior than each constituent copolymer. With the increase of the volume fraction of the short diblocks in the blends, multiple transitions from a long-period lamellar phase to phases with nonzero interfacial curvatures including cylindrical and spherical phases, and finally to a short-period lamellar phase or disordered phase, are predicted. In particular, consistent with experiments, the theory predicts that the cylindrical phase is stabilized over a wide blending compositions region in the strong segregation region, even though the two constituent diblock copolymers are both lamella-forming. When the ratio R is large enough, macrophase separation occurs over a wide range of blending compositions in a relatively strong segregation regime. Various coexisting phases, including those of lamellar and disorder, lamellar and cylindrical, cylindrical and cylindrical, cylindrical and disorder, spherical and disorder, and cylindrical and spherical, are predicted. In addition, the density profiles of the typical ordered structures are presented in order to understand the self-organization of the different copolymer chains.

Phase behavior of blends of two AB diblock copolymers, with the long one at relatively strong segregation, is studied using the selfconsistent field theory, focusing on the effect of compositions of the two block copolymers and their length ratio. In order to carry out extensive calculations on the large parameter space, a unit-cell approximation is employed, in which the mean-field equations are solved using a Bessel function expansion. Phase diagrams are constructed for four typical series of blends by comparing the free energies of the different ordered phases including lamellae, cylinders, and spheres. The results reveal that the competition between macro-and microphase separation leads to complex phase behavior. When the length ratio of the two block copolymers is small, the short copolymers tend to segregate to the A/B interfaces, inducing multiple order-order phase transitions including reentrant phase transitions in some blends. When the length ratio of the two diblock copolymers is sufficiently large, macrophase separation may take place. The predicted phase diagrams are compared with available experiments. Density profiles of typical ordered structures are presented to understand the self-organization of the polymer chains. The energetics of the blends is introduced to account for the appearance of the macro-and microphase separations.

The bamboo fiber (BF)-reinforced polylactic acid (PLA) composites were prepared using the twin-screw extruder and injection molding. Thermal gravimetric analyzer results indicated the thermal stability of BF/PLA composites decreased with increasing BF content. Differential scanning calorimeter and X-ray diffraction curves showed that BF played a role as a nucleating agent, but the crystallinity of composite materials decreased with the increasing BF content. The melt flow rate of composites reduced with the increase in BF content, resulting in a poorer processing property. The processability of the composites was improved with the addition of high molecular polyethylene glycol (PEG). Mechanics performance test showed that tensile strength and bending strength of composites increased at low loading with the BF content increased then decreased when the loading continued to increase. The tensile strength of the composite materials reached 65.46 MPa when alkali-treated BF (ABF) content was 20 wt %. The flexural strength of the composites reached 97.94 MPa when ABF content was 10 wt %. Impact performance has also been improved. PEG-20000 was the best plasticizer among the PEG-6000，PEG-10000, and PEG-20000. When the component of PEG was 10 wt %, the elongation increased by 56%. The scanning electron microscopy (SEM) result showed that the fracture of the composites was smooth, most ABF were wrapped in matrix and distribution of ABF in PLA matrix was more uniform. It means that interfacial compatibility of bamboo fiber and PLA improved after BF modified by alkali. High molecular weight PEG enhance melt flow ability of polymer, result in fibers were further enclosed in the PLA matrix and increase properties of composites.