Haining Na

Highly recoverable rosin-based shape memory polyurethanes

Improving the phase separation and stability of the hard segment domains at the same time is the novel method reported here to improve the recovery of thermoplastic shape memory polyurethanes (SMPUs) at high strain (>1000%). The shape recovery of the corresponding SMPUs with a more than 1000% strain can reach about 96% at room temperature in 3 min, the recoverable strain (emax − epermanent) is more than 960%, which is nearly 2.5 times that of the best value (400%) previously reported.

How a bio-based epoxy monomer enhanced the properties of diglycidyl ether of bisphenol A (DGEBA)/graphene composites

A bio-based epoxy monomer (GA-II) was synthesized from renewable gallic acid. The aromatic group contained made it capable of being absorbed onto the surface of graphene via strong π–π interactions, which was proven by Raman spectra and UV spectra. The GA-II anchored graphene was easily homogeneously dispersed in the epoxy resin. After solidification, the graphene/epoxy composites demonstrated superior performances in terms of good mechanical properties, excellent thermal conductivity, as well as high electrical conductivity. With the addition of only 2 wt% GA-II/graphene, the tensile strength, tensile modulus, flexural strength and flexural modulus of the composites were improved by 27%, 47%, 9% and 21%, respectively. The thermal and electrical conductivities were also improved by 12-fold (from 0.15 to 1.8 W m−1 K−1) and 8 orders (from 7.0 × 10−15 to 3.28 × 10−5 s cm−1), respectively. This work provided us with an environmentally friendly agent with high efficiency for graphene dispersion and demonstrated an efficient method for fabricating epoxy/graphene composites with superior properties.

A novel facile two-step method for producing glucose from cellulose.

A two-step acid-catalyzed hydrolysis methodology is established to effectively hydrolyze cellulose to glucose with high yield and selectivity under mild conditions. In multi-steps hydrolysis, the difficulty of cellulose can be effectively reduced under mild conditions. In the first step, microcrystalline cellulose was depolymerized in phosphoric acid to cellulose oligomer at 50°C. Then the oligomer was precipitated by ethanol and hydrolyzed with dilute sulfuric acid in the second step. 87.7% total reducing sugars and 57.8% glucose was released from the two-step hydrolysis process. In addition, with the assistance of microwave in the second step, the yield and selectivity of glucose can be improved to 73.3% and 80.1% by only 5 min hydrolysis. The two-step hydrolysis exhibits an effective process to produce glucose in cellulose hydrolysis. The enhancement of hydrolysis reactivity is considered to be controlled with the decrease of crystallinity and degree of depolymerization of cellulose.

Measurement of Adhesion Work of Electrospun Polymer Membrane by Shaft-Loaded Blister Test

The work of adhesion at the interface of electrospun membrane and rigid substrate is measured by a shaft-loaded blister test (SLBT). Poly(vinylidene fluoride) (PVDF) were electrospun with an average fiber diameter of 333 ± 59 nm. Commercial cardboard with inorganic coating was used to provide a model substrate for adhesion tests. In SLBT, the elastic response PVDF was analyzed and its adhesion energy measured. The average value of the adhesion work is 206 ± 26 mJ/m(2). Elastic modulus of electrospun membrane obtained by SLBT is found to be 23.42 ± 2.69 MPa, which is consistent with the value obtained from standard tensile tests. The results show SLBT presented a viable methodology for evaluating the adhesion energy of electrospun polymer fabrics.

Soft segment free thermoplastic polyester elastomers with high performance

A soft segment free thermoplastic polyester elastomer is fabricated by controlling the stereochemical structure of molecular chains with the utilization of the cis 1,4-cyclohexylene ring moiety (cis-CHRM) in poly(butylene 1,4-cyclohexanedicarboxylate) (PBC). PBC with 71% cis-CHRM exhibits good elasticity with shape recovery rates of 64% at 200% strain and 92% at break, tensile modulus, strength and elongation at break at 111 and 18 MPa and 1230%, respectively.

Hydrolysis behavior of regenerated celluloses with different degree of polymerization under microwave radiation

This work studied the hydrolysis behavior of regenerated celluloses (RCs) with different degree of polymerization (DP) by using the catalyst of dilute acid under microwave radiation. Results showed that the DP had a considerable influence on hydrolysis of cellulose. The reactivity of RCs was significantly improved when DP was lower than 51. The highest sugar yield of 59.2% was achieved from RC with lowest DP of 23 at 160 °C for 15 min. But the lowest yield of 32.6% was obtained when RC with highest DP of 132 was used. Recrystallization of cellulose was found to hinder the further hydrolysis particularly with the high DP. The effect of recrystallization can be reduced by the decrease of DP of RCs. This research demonstrates that the DP of RCs plays a crucial role on hydrolysis and it provides a preliminary guide based on DP to find a suitable pretreatment method for cellulose hydrolysis.

Responsive behavior of regenerated cellulose in hydrolysis under microwave radiation

This work studied the responsive behavior of regenerated cellulose (RC) in hydrolysis under microwave radiation. Four types of RC with different crystallinity (Cr) and degree of polymerization (DP) are produced to evaluate the reactivity of RC by step-by-step hydrolysis. Results show Cr is the key factor to affect the reactivity of RCs. With hydrolysis of amorphous region and the formation of recrystallization, the Cr of RC reaches a high value and thus weakens the reactivity. As a result, the increment of cellulose conversion and sugar yield gradually reduces. Decrease of the DP of RC is helpful to increase the speed at the onset of hydrolysis and produce high sugar yield. But, there is no direct influence with the reactivity of RC to prolong the time of pretreatment. This research provides an accurate understanding to guide the RC preparation for sugar formation with relative high efficiency under mild reaction conditions.

Role of cis-1,4-cyclohexanedicarboxylic acid in the regulation of the structure and properties of a poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) copolymer

A unique non-planar ring structure 1,4-cyclohexanedicarboxylic acid (CHDA) is introduced to synthesize a poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) (PBAC) copolyester. The impact of the stereochemistry of CHDA on the structure and properties of PBAC, especially the role of cis-CHDA in tuning the thermal, tensile and elastic properties of PBAC is explored in depth. Instead of considering PBAC as a diblock random copolymer consisting of poly(butylene adipate) (PBA) and poly(butylene 1,4-cyclohexanedicarboxylate) (PBC), our results reveal that PBAC can be considered as a random copolymer consisting of actually three blocks, namely PBA, a PBC unit with only trans-CHDA (trans-PBC), and PBC unit with only cis-CHDA (cis-PBC). The role of cis-CHDA is found to be rigid which initiates a high modulus and strength, and soft which results in a decreased melting temperature and increased elongation at break and elasticity.

Incorporation of 1,4-cyclohexanedicarboxylic acid into poly(butylene terephthalate)-b-poly(tetramethylene glycol) to alter thermal properties without compromising tensile and elastic properties

Thermal and tensile properties of thermoplastic elastomers (e.g. poly(butylene terephthalate)-b-poly(tetramethylene glycol) (PBT–PTMG)) are usually tuned by changing the composition of hard and soft segment parts. Simply increasing the amount of soft segment results in a lower melting temperature and better elastic properties, but the thermal stability and tensile properties are inevitably sacrificed. In this work, by incorporation of an aliphatic ring structure (i.e. 1,4-cyclohexanedicarboxylic acid) (CHDA) to partially replace the aromatic ring (i.e. terephthalic acid) in PBT-PTMG, the properties of the material can be tuned in such a way that the melting temperature decreases, while the thermal stability, tensile and elastic properties are not compromised. Moreover, manipulation of the stereo-chemistry of the CHDA unit discloses the “elastic” nature of the non-planar ring structure. Samples with a greater amount of cis-CHDA tend to have better tensile and elastic properties compared with their trans-CHDA counterparts.

Synthesis of poly(butylene terephthalate)-poly(tetramethylene glycol) copolymers using terephthalic acid as starting material: A comparation between two synthetic strategies

Poly(butylene terephthalate)-poly(tetramethylene glycol) (PBT-PTMG) copolymer is prepared with terephthalic acid (PTA) rather than its dimethyl ester (DMT) as starting material by a two-step melt polycondensation. This process includes the synthesis of PBT prepolymer from PTA with 1,4-butanediol (BDO) in the first step, followed by the synthesis of PBT-PTMG copolymer from PBT prepolymer with PTMG in the second step. The molecular weight, composition as well as thermal and mechanical properties of the products from the two-step melt polycondensation are compared with the properties of the PBT-PTMG from the traditional one-step melt polycondensation. When the PTMG content is low, there is only slight difference in molecular weight, composition, thermal and mechanical properties among PBT-PTMG copolymers obtained from these two methods. However, when the PTMG content is high, only the two-step strategy is able to give high molecular weight products, and the products have comparable thermal and mechanical properties with those from traditional one-step strategy using DMT as starting material.