Biomimetic, stimuli-responsive nanocomposites were made using either poly(styrene-co-butadiene) (SBR) or polybutadiene (PBD) as the hydrophobic, low-modulus matrix and hydrophilic cellulose whiskers isolated from tunicates (TW) as the high-modulus filler. These materials were prepared using a template approach, which involves the formation of a percolating TW network and filling this template with either of the matrix polymers. Dynamic mechanical analysis (DMA) studies of the dry nanocomposite films reveal that the incorporation of TWs into the rubbery polymers increases the tensile storage modulus E′ significantly. The reinforcement is attributed to the formation of a three-dimensional TW network within the SBR and PBD matrices. The incorporation of the TWs did not affect the main relaxation temperature of the matrix SBR polymer, suggesting weak nanofiller− polymer interactions. Thus, the reinforcement is primarily on account of the nanofiller−nanofiller interactions, which involve hydrogen bonding. Interestingly, submersion of these hydrophobic matrix nanocomposites in water results in dramatic softening, consistent with disengagement of the TW network as a consequence of competitive hydrogen bonding with water. The kinetics of the modulus change and the amount of water uptake were shown to depend on the TW content. Given the hydrophobic nature of the matrices, it is proposed that the TWs create a percolating network of hydrophilic channels within the hydrophobic SBR and PBD matrices.

Biomimetic, stimuli-responsive polymer nanocomposites based on a hydrophobic styrene-butadiene rubber (SBR) matrix and rigid, rod-like cellulose nanocrystals (CNCs) isolated from cotton were prepared by three different approaches, and their properties were studied and related to the composition, processing history, and exposure to water as a stimulus. The first processing approach involved mixing an aqueous SBR latex with aqueous CNC dispersions, and films were subsequently formed by solution-casting. The second method utilized the first protocol, but films were additionally compression-molded. The third method involved the formation of a CNC organogel via a solvent exchange with acetone, followed by infusing this gel, in which the CNCs form a percolating network with solutions of SBR in tetrahydrofuran. The thermomechanical properties of the materials were established by dynamic mechanical thermal analysis (DMTA). In the dry state, all nanocomposites show much higher tensile storage moduli, E', than the neat SBR or the SBR latex. E' increases with the CNC content and depends strongly on the processing method, which appears to influence the morphology of the SBR nanocomposites produced. The highest E' values were observed for the solution cast samples involving an SBR latex, where E' increased from 3 MPa for the neat SBR to ca. 740 MPa for the nanocomposite containing 20% v/v CNCs. Upon submersion in deionized water, a dramatic reduction of E' was observed, for example from 740 to 5 MPa for the solution-cast nanocomposite containing 20% v/v CNCs. This change is interpreted as a disengagement of the percolating CNC network, on account of modest aqueous swelling and competitive hydrogen bonding of water molecules with the CNCs. It is shown that the method of preparation also influenced the swelling behavior and kinetics of modulus switching, consistent with different arrangements of the CNCs, which serve as channels for water absorption and transport within the hydrophobic SBR matrix.

BACKGROUND: The thermomechanical performance of poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is associated with its crystallization. Enhanced nucleation using a stearate-functionalized synthetic layered double hydroxide (LDH) presents a potential solution. RESULTS: PHBV crystallization varied with concentration of LDH. At lower LDH concentration, thermal history-induced coldcrystallization was present. The extent of this order-disorder transition decreased with increasing LDH concentration and was completely eliminated at 7 wt% LDH. PHBV did not have a melt recrystallization peak but the introduction of LDH resulted in an increasingly pronounced melt recrystallization with increasing LDH concentration. Polarized optical microscopy coupled with differential scanning calorimetry and wide angle X-ray diffraction (WAXD) analysis indicated increased lamella thickness in the nanocomposites compared to pure PHBV. WAXD and transmission electron microscopy showed that the nanocomposites had an intercalated but aggregated dispersion. CONCLUSION: The concentration of nanofiller provides unique effects in PHBV. Mechanical performance was found to scale with composition as determined using dynamic mechanical analysis and tensile testing.

ABSTRACT:The detrimental effect of cell adhesion on polymer surfaces has been a limiting factor in the medical deployment of many implants. We examined the potential to decrease cell proliferation while simultaneously increasing mechanical performance through Zn-Al layered double hydroxide (LDH) organically modified with ibuprofen dispersed in poly(L-lactic acid) (PLLA). These composites are commonly referred to as nanocomposites. The thermophysical and mechanical properties of the hybrids were studied with wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. The WAXD and TEM results indicated that intercalated and exfoliated nanocomposites were obtained. The storage modulus, tensile modulus, and ultimate tensile strength were improved. The LDH affected the cold crystallization and reduced the thermal stability of the neat PLLA. Smooth muscle cells were used for in vitro studies of the nanocomposites. It was found that the hybrids reduced cell proliferation, and the amount of cell reduction was related to ibuprofen release.

Conductometric titrations of the carboxylated CNCs with different charge density.From the conductometric titration plot, the difference between the points where the trend lines intersect is taken, representing the amount of 0.01 M NaOH used between these points. This value is