Enhanced mechanical and long-lasting antibacterial properties of starch/PBAT blown films via designing of reactive micro-crosslinked starch

A functional starch (TPS-E) was designed and constructed by incorporating epoxy soybean oil (ESO) and an antibacterial agent polyhexamethylene guanidine hydrochloride (PHMG), then the film was prepared by reaction extrusion and blow molding using TPS-E and poly(butylene adipate-co-terephthalate) (PBAT). The micro-crosslinking structure, forming through ring-opening reaction between the epoxy active site of TPS-E and the end group of PBAT, improved the compatibility of starch/PBAT blend and reduce the dispersed starch phase size, leading to significantly increase the tensile strength. Compared to starch/PBAT films, the tensile strength of TPS-E/PBAT in the longitudinal direction increase by 112% with the same starch content of 30%. Furthermore, these TPS-E/PBAT films demonstrated long-lasting antibacterial performance with a 98% inhibition ratio even after 10 cycles, without any observed leaching of the antibacterial agent, highlighting the high coupling efficiency of PHMG. TPS-E with the degradable ESO also promotes the degradation of PBAT. Thus, an important method of synergistic improving the mechanical, degradable and antibacterial properties of blown films through the design of reactive micro-crosslinked starch structures was established.

Effect of N,N'-Dicyclohexyldicarboxamide Homologues on the Crystallization and Properties of Isotactic Polypropylene

Application of nucleating agents is the most versatile and industrially applied way to manipulate the crystalline structure of isotactic polypropylene (iPP). Various materials possess a nucleating effect, but from the viewpoint of dispersibility, the partially soluble ones are the most advantageous. Our objective was to synthesize new N,N'-dicyclohexyldicarboxamide homologues and study their applicability as nucleating agents in iPP. Carbon-13 nuclear magnetic resonance (¹³C NMR) and infrared spectroscopy were used to prove that the synthesis reactions were successful. Thermal stability of the compounds was investigated with simultaneous thermal analysis. Nucleating efficiency and solubility were characterized by polarized light microscopy and differential scanning calorimetry. Polarized light microscopy was also applied to study the effect of novel additives on the morphology of iPP. The properties, important from the viewpoint of applicability, were also investigated. Tensile tests were performed to characterize the main mechanical properties, and standard haze measurements were performed to characterize optical properties. It can be concluded that the investigated compounds are partially soluble nucleating agents and influence the crystalline structure of iPP. Most of the studied compounds have a moderate nucleating efficiency, but a very interesting dendritic structure develops in their presence. Two of them proved to be non-selective β-nucleating agents, which result in a remarkable improvement of impact resistance and higher opacity.

The effects of blend ratio and storage time on thermoplastic starch/poly(butylene adipate-co-terephthalate) films

The objective of this work was to investigate blend ratio and storage time effects on the morphological, mechanical, and thermal properties of thermoplastic starch/poly(butylene adipate-co-terephthalate) (TPS/PBAT) films. TPS was prepared from plasticized cassava starch using a twin-screw extruder. TPS was subsequently melt-blended with PBAT with varied weight ratios (i.e., 20/80, 40/60 and 60/40) and blown to form TPS/PBAT films. It was found that increasing the TPS/PBAT ratio to 40/60 led to improved distributions of polymeric components and increased PBAT crystallization temperatures while reducing TPS melting transitions and tensile properties of TPS/PBAT films. After three months of storage at 30 °C, the tensile strength and secant modulus at 2% strain of TPS/PBAT films increased due to recrystallization of both TPS and PBAT. Blend ratios were the primary determinant for changes in TPS/PBAT film elongation at break with this storage time. Elongation at break decreased at low TPS:PBAT ratios (i.e., 20/80) and increased at high blend ratios (i.e., 60/40). The recrystallization of both TPS and PBAT components were observed from XRD and DSC analyses. Results obtained from both techniques confirmed the formation of additional crystalline structures of individual components during storage. The recrystallization phenomena also affected thermal transition temperatures of blend components. The crystallization temperature of PBAT-rich phase increased as starch could act as nucleating sites for PBAT. Using DMA, the tan δ curve of TPS/PBAT film exhibited two sharp individual peaks corresponding to the glass transitions of PBAT-rich and starch-rich phases. The tan δ of TPS-rich phase shifted to higher temperature due to recrystallization of TPS-rich phase.

An Effective α/β Nucleating Agent Compoundfor the Preparation of Polypropylene

The crystallization behavior and mechanical properties were investigated by mixing the traditional α-form nucleating agent (sodium benzoate, SB) and commercialized β-form nucleating agent (TMB-5) in isotactic polypropylene (iPP). Mechanical properties were evaluated by universal testing machines. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were conducted to illustrate the crystallization behavior. Polarized optical microscopy (POM) was adopted to observe the crystal morphologies. The experimental results show that the weight ratio of two types of nucleating agents determines the final crystal structure and mechanical properties of iPP. When the weight ratio of [SB] : [TMB-5] is 4 : 1, the impact strength and flexural modulus of iPP reach a maximum value. Compared with the single component β-form nucleating agent, the compound nucleating agent exhibits significant synergistic effect and shows better mechanical properties. It is expected that this new nucleation system will have potential industrial applications.

Effects of isomorphic poly(butylene succinate-co-butylene fumarate) on the nucleation of poly(butylene succinate) and the formation of poly(butylene succinate) ring-banded spherulites

The composition of isomorphic PBSF can dramatically affect the nucleation efficiency, the formation temperature of ring-banded spherulite and the band spacing of the PBS.

Facilely assess the soluble behaviour of the β-nucleating agent by gradient temperature field for the construction of heterogeneous crystalline-frameworks in iPP

Nucleating agent (NA) species with solubility and self-assembly abilities can readily and effectively manipulate the crystalline morphology of semicrystalline polymers through the construction of heterogeneous frameworks prior to the primary crystallization of basal resins. However, the solubility of NA species is difficult to assess by the current traditional methods. In this study, gradient temperature field (g-T field) was utilized for the first time to ascertain the dissolution and self-assembly behaviors of β-NA in the melts of isotactic polypropylene (iPP). The g-T field technique can facilely assess the soluble behavior of β-NA by determining the transformation between several NA frameworks, namely the needle-, flower- and dendrite-like supramolecular structures. Clarifying the soluble behavior of β-NA is of great significance to guide the formation of various crystalline frameworks under the homo-temperature fields and control the resultant crystalline morphology of β-modified iPP. Some interesting findings are summarized as follows: (1) an in situ observation under the g-T field clearly indicates the sequential occurrence of various nucleation and crystallization events in the same observed window, and proves the migration of well molten β-NA, (2) the exact correlation between Tf and framework type reveals that an abrupt transformation (over the narrow temperature range of 1 °C) occurred between needle-like and dendrite-like frameworks, (3) the primary crystallization of iPP is strongly dependent on the construction mode of the β-NA framework.

Enhanced nucleation of polypropylene by metal–organic frameworks (MOFs) based on aluminium dicarboxylates: influence of structural features

Metal–organic frameworks (MOFs) based on aluminium dicarboxylates having butterfly-like structure and hydrophobic interaction offers a new platform for the enhanced nucleation of isotactic polypropylene (iPP).

The role of the molecular structure of carboxylate-alumoxanes in the enhanced nucleation of polypropylene

The unique, butterfly-like structure of carboxylate-alumoxanes offers polypropylene segments a shape selective cavity to fit in and facilitate a favourable interaction for enhanced nucleation.

Thermal Properties and Morphology Characteristics of a PP Mono-Filament and its Foam

The polypropylene (PP) mono-filament is an alternative material that can be used for insulation, packaging, and polymer composite applications. In this study, PP mono-filaments were prepared by extrusion free-fall at temperatures of 190, 200, and 210°C through a micro extrusion die with a diameter of 900 μm. The free-fall speeds of the filament were controlled by a gear pump driving at speeds ranging from 12.5 to 20.0 min−1, and the extrudates were cooled at room temperature. The PP mono-filaments were subsequently foamed by a batch foaming process with sc-CO2 as the blowing agent at foaming temperatures of 165, 170, 175 and 180°C. The thermal properties and crystallinity of the prepared filaments and their foams were investigated using a DSC. The foam morphology and isotropic foam properties were characterized by SEM micrographs. The results show that the various morphologies of the PP mono-filament foams deviated from the isotropic foam behavior and had isotropic foam index values in the range of 1.1 to 2.3. In addition, the PP mono-filament that was foamed at 175°C expanded in the longitudinal direction and exhibited the highest expansion ratio, but its degree of crystallinity decreased compared to the mono-filaments. PP mono-filament foam represented a narrow crystallization temperature range and crystallization time than mono-filament and tended to a faster crystalline growth.

Effect of the molecular structure of the polymer and nucleation on the optical properties of polypropylene homo- and copolymers

Two soluble nucleating agents were used to modify the optical properties of nine PP homo- and random copolymers. The ethylene content of the polymers changed between 0 and 5.3 wt %. Chain regularity was characterized by the stepwise isothermal segregation technique (SIST), while optical properties by the measurement of the haze of injection molded samples. Crystallization and melting characteristics were determined by differential scanning calorimetry (DSC). The analysis of the results proved that lamella thickness and change in crystallinity influence haze only slightly. A model was introduced which describes quantitatively the dependence of nucleation efficiency and haze on the concentration of the nucleating agent. The model assumes that the same factors influence the peak temperature of crystallization and optical properties. The analysis of the results proved that the assumption is valid under the same crystallization conditions. The parameters of the model depend on the molecular architecture of the polymer. Chain regularity determines supermolecular structure and thus the dependence of optical properties on nucleation.