Tensile Properties of Polylactide/Poly(ethylene glycol) Blends

The blends of polylactide (PLA) and poly(ethylene glycol) (PEG) with different contents (0, 5, 10, 15, and 20 wt%) and molecular weights (\( \overline{M}_{w} \) 6000, 10,000 and 20,000, called respectively as PEG 6000, PEG 10,000, and PEG 20,000) were prepared by means of melt blending method. The effects of tensile speed, content and molecular weight of the PEG on the tensile properties of the PLA/PEG blends were investigated using a universal testing machine at 24 °C. With increasing tensile speed, the tensile modulus, strength and stress at break of the PLA/PEG blends marginally increased, while the tensile modulus and stress at break declined non-linearly, and the tensile strength dropped nearly linearly with increasing PEG 10,000 content. When the PEG 10,000 content was 5–15 wt%, the tensile strain at break of the PLA/PEG 10,000 blend markedly increased, and then decreased as the PEG 10,000 content exceeded 15 wt%. With increasing the molecular weight of PEG, tensile modulus and strength increased, whereas the tensile strain at break decreased. This showed that the application of right amount of lower molecular weight PEG was more conducive to improving the tensile toughness of the PLA/PEG blends, which was attributed to its better miscibility with PLA and increased mobility of PLA molecular chains.     

Novel Tough Crystalline Blends of Polylactide with Ethylene Glycol Derivative of POSS

Blending of polylactide (PLA) with low stereoregularity and polyhedral oligomeric silsesquioxane grafted with arms of poly(ethylene glycol) methyl ether, acting as a plasticizer, allowed us previously to obtain a novel stable elastomeric-like material. The present contribution focuses on the properties of semi-crystalline PLA plasticized with this compound. Melt blends of PLA with 5–15 wt% of the plasticizer, were compression molded, quenched and annealed, which enabled cold-crystallization. The glass transition temperature of the blends and their drawability depended on their crystallinity and plasticizer content. The best ductility was reached at the plasticizer content of 15 wt%; the achieved strain at break was 6.5 (650%) and 1.3 (130%), for the quenched and annealed material, respectively. The latter value exceeded 20 times the strain at break of neat crystalline PLA. The tensile toughness of the annealed 15 wt% blend was 12 times larger than that of crystalline PLA. Moreover, annealing of 15 wt% blend improved its yield strength by 40%. Despite the two peaks of the loss modulus, indicating the two glass transitions in this blend, no heterogeneities were found by scanning electron microscopy, indicating that the plasticizer enriched phase formed instead of distinct inclusions of the plasticizer.     

Block Copolymers Containing (R)-3-Hydroxybutyrate and Isosorbide Succinate or (S)-Lactic Acid Mers

A new aliphatic block copolyester was synthesized in bulk from transesterification techniques between poly((R)-3-hydroxybutyrate) (PHB) and poly(isosorbide succinate) (PIS). Additionally, other two block copolyesters were synthesized in bulk either from transesterification reactions involving PHB and poly(l-lactide) (PLLA) or from ring-opening copolymerization of l-lactide and hydroxyl-terminated PHB, as result of a previous transesterification reactions with isosorbide. Two-component blends of PHB and PIS or PLLA were also prepared as comparative systems. SEC, MALDI-TOF mass spectrometry (MALDI-TOFMS), ¹H and ¹³C NMR spectroscopy, WAXD, solubility tests, and TG thermal analysis were used for characterization. The block copolymer structures of the products were evidenced by MALDI-TOFMS, ¹³C NMR, and WAXD data. The block copolymers and the corresponding binary blends presented different solubility properties, as revealed by solubility tests. Although the incorporation of PIS sequences into PHB main backbone did not enhance the thermal stability of the product, it reduced its crystallinity, which could be advantageous for faster biodegradation rate. These products, composed of PHB and PIS or PLLA sequences, are an interesting alternative in biomedical applications.     

Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)/Polylactide Blends: Thermal Stability,Flammability and Thermo-Mechanical Behavior

Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) with different PHBV/PLA weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) were prepared by melt compounding. Their mutual contributions in terms of thermal stability, flammability resistance, mechanical properties and rheological behavior were investigated. The study showed that the increase in PLA content in PHBV/PLA blends leads to enhanced properties. Consequently, thermal stability and flammability resistance were improved. Further, the rheological measurements indicated an increase in storage modulus and loss modulus of PHBV matrix by addition of PLA.     

Synthesis and Properties of Poly(d,l-lactide-co-p-dioxanone) Random and Segmented Copolymers

Two different polymerization routes, one-step and two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (PDO) monermers using stannous octoate [Sn(Oct)₂]/n-dodecanol as the initiating system, were employed to synthesize poly(d,l-lactide-co-p-dioxanone) P(LA-co-PDO) random and segmented copolymers with different compositions and chain microstructure. For the two-step copolymers, the average sequence lengths of the lactidyl (L_LA) and dioxanyl (L_PDO) units calculated from the ¹H-NMR spectra were much longer than those values for the one-step copolymers with the same LA/PDO feed ratio. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline even when the PDO content was as low as 14.5 mol%, while the one-step copolymers were completely amorphous with PDO content below 60.6 mol%. However, irrespective of polymerization route, both types of copolymers displayed a single glass transition temperature that was in a linear relation with composition. The decrease of maximum decomposition temperature of the copolymers was in accordance with the decrease of L_PDO value. The mechanical and degradation properties of the copolymers were significantly affected by both the polymerization route and the chemical composition as well. In conclusion, the properties of P(LA-co-PDO) copolymers could be adjusted conveniently to meet specific applications by changing the composition and microstructure of the copolymers via different polymerization routes.     

Modification of Aliphatic Polyesters and Their Reactive Blends with Starch

Modified polycaprolactone was synthesized by melt reaction of PCL and reactive monomers such as glycidyl methacrylate (GMA) and maleic anhydride (MAH) in the presence of benzoyl peroxide in Brabender mixer. MAH showed a different grafting phenomenon compared to GMA. The reaction mechanism was discussed with different reactive monomers. Reactive blends of the PCL-g-GMA and the gelatinized starch with glycerin were prepared and their mechanical properties and biodegradabilities were investigated. Reactive blends of PCL-g-GMA and starch showed well-dispersed starch domain in the matrix and better mechanical strength than the unmodified PCL/starch blend. However, the reaction between PCL-g-GMA and starch induced a crosslinking during the reactive blending and this crosslinking in the blend lowered the biodegradation of the blend during the composting test. The biodegradability was investigated by the weight loss and surface morphology change of the blend in the composting medium.     

Preparation and Characterization of Xylan Derivatives and Their Blends

Although hemicellulose is found widely in nature, it is currently under-utilized as a raw material for commercial applications. It would be desirable to find new uses for hemicellulose in order to add value to this agro-based material. A common type of hemicellulose is xylan, which is found in a number of wood species and in cotton. In this work we prepared cationic and anionic xylan derivatives and characterized them by ¹³C NMR, FT-IR, size exclusion chromatography (SEC), thermal analysis, and rheology. In particular, the ¹³C NMR spectra of carboxymethyl xylan (CMX) and quaternary ammonium-adducted xylan (QAX) were fully assigned with the help of samples with different degrees of substitution. SEC indicated that the beechwood xylan showed a bimodal molecular weight distribution, but with derivatization the distribution tended to become unimodal. Thermal analysis and rheology studies did not uncover any surprises; the solution of xylan and its derivatives exhibited mostly Newtonian behavior. The blends of CMX and QAX produced a precipitate at almost all ratios, indicating the formation of a polyelectrolyte complex. When cationic and anionic xylan samples were added together to paper, the paper dry strength increased. Thus, the combination of cationic/anionic xylan may be of interest in selected applications.     

Synthesis and Characterization of Biodegradable Starch-Polyacrylamide Graft Copolymers Using Starches with Different Microstructures

The effects of starch structures, in particular amylose content, on grafting reactions were investigated using thermal gravimetric analysis (TGA), nuclear magnetic resonance, X-ray diffraction (XRD). As a model system, corn starches with different amylose contents (0, 26, 50 and 80 %) were grafted onto acrylamide to produce superabsorbent polymers (SAPs). The weight loss measured by TGA at different temperature was used to analyze the grafting ratio in quantity. In general, the grafting ratio increased (about 10 %) with increasing starch amylose content, and graft chain segment lengths were much lower for the amylopectin-rich (waxy) starch. The high molecular weight and branched structure of the amylopectin reduced the mobility of the polymer chains and increased viscosity, which resulted in resistance to chain growth. The water absorption capability was increased with increasing amylose content for the starch-based SAPs. XRD detection showed that the crystalline structure of all starches was destroyed after grafting reactions. The thermal stability of the polyacrylamide grafted onto the starches increased by about 10 °C, which could be explained by the strong bonding between the grafted polymer chains and the starch matrices.     

Processing and Thermal Behaviors of Poly (Butylene Succinate) Blends with Highly-Filled Starch and Glycerol

Fully-biodegradable and highly-filled thermoplastic starch plasticized with glycerol (GTPS)/poly (butylene succinate) (PBS) blends were prepared by Haake Mixer. Processing properties, thermal behaviors including melting and crystallization behavior, crystal structure, and compatibility of the blends were investigated using differential scanning calorimeter (DSC), wide angle X-ray diffractometer (WAXD), scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). The maximum and equilibrium torques decreased with the rising of glycerol contents and the dropping of PBS contents. GTPS30/PBS blends exhibited double melting endothermic peaks in the DSC thermograms, which related to the crystallization behavior and compatibility of the blends, but no double peaks for GTPS40/PBS. The addition of starch and glycerol could lead to higher crystallinity and lower crystallization rate of PBS, but would not change the crystal types and crystallite sizes of PBS according to DSC and WAXD analysis. SEM and DMA results gave the evidence to confirm the better compatibility of GTPS40/PBS. Besides, higher storage modulus in glassy state of GTPS/PBS blends than PBS could be seen from DMA analysis, which was the contrary in rubbery state.     

Effects of UV/Photo-Initiator Treatments on Enhancement of Crystallinity of Polylactide Films and Their Physicochemical Properties

Effects of UV/photo-initiator treatments on crystal formation and properties of polylactide (PLLA) films are investigated. Camphorquinone and riboflavin photo-initiator solutions in methanol are employed in the treatment of amorphous quenched PLLA films. Results from FTIR, ATR-FTIR, DSC, XRD, and SEM show evidence of crystalline domain formation dispersed throughout the film. ¹H NMR and GPC results suggest that the molecular weights of the polymer slightly decrease after the treatment. This indicates that the treatment leads to a diffusion of the photo-initiators molecules through the film matrix, resulting in a low degree of PLLA chain scissions, and formation of carboxylic acid and hydroxyl polar end groups. This, in turn, induces PLLA crystallization, which imposes profound effects on surface wettability and physical and mechanical properties of the samples. The process can be applied in optimizing properties of PLLA films with shorter treatment times, compared to other methods, which is suitable for use in various fields; especially those that require specific characteristics like biomedical, packaging and environmental applications.     

Mechanical Properties and Morphology of Polypropylene/Poly(ethylene-co-octene) Blends

The polypropylene (PP)/poly(ethylene-co-octene) (POE) blends was prepared by means of a twin screw extruder in a range of temperature from 185 to 195 °C. The mechanical properties including tensile, flexural and impact of the PP/POE blends were measured at room temperature to identify the effect of the POE content on the mechanical properties. It was found that the Young’s modulus, tensile strength and tensile elongation at break decreased nonlinearly with increasing the POE weight fraction. While the V-notched and unnotched impact fracture strength increased nonlinearly with an increase of the POE weight fraction. The flexural modulus and strength decreased roughly linearly with increasing the POE weight fraction. Furthermore, the impact fracture surface of the blends was observed by using a scanning electronic microscope and the toughening mechanisms were discussed.     

Biodegradable Poly(lactic acid) Blends with Chemically Modified Polyhydroxyoctanoate Through Chain Extension

Poly(lactic acid) (PLA) was blended with chemically modified Polyhydroxyoctanoate (mPHO) using a Haake twin-screw mixer. Due to the melt viscosity disparity between the two components, PHO was reacted with Hexamethylene diisocyanate (HDI) used as a chain extender to produce high molecular weight for improving compatibility and processability with PLA. The number average and weight average molecular weight of the PHO, reacted with 0.55 wt% HDI, were increased 314 and 275%, respectively, compared with those of the unmodified PHO. The blends were characterized for rheological, thermal, and mechanical properties. Infrared spectra confirmed the formation of the urethane linkages in mPHO. The shear viscosity, as a function of shear rate or shear stress, decreased with an increase in mPHO content, indicating that the PLA/mPHO blends show shear-thinning behavior along with the power-law model. DSC thermograms showed that the two components in the blends were found with two crystalline phases and two amorphous phases confirming the coexistence of two immiscible components. Tensile results indicated that tensile strength for blends decreased with increasing mPHO content up to 80%. A decrease in elastic modulus, as well as an increase in elongation at break, was seen as a function of mPHO content. Results of aging tests showed that the mechanical properties of the blends also dropped more at a higher PLA level when compared with those of the unaged samples.     

Starch, Poly(lactic acid), and Poly(vinyl alcohol) Blends

Research on biodegradable materials has been stimulated due to concern regarding the persistence of plastic wastes. Blending starch with poly(lactic acid) (PLA) is one of the most promising efforts because starch is an abundant and cheap biopolymer and PLA is biodegradable with good mechanical properties. Poly(vinyl alcohol) (PVOH) contains unhydrolytic residual groups of poly(vinyl acetate) and also has good compatibility with starch. It was added to a starch and PLA blend (50:50, w/w) to enhance compatibility and improve mechanical properties. PVOH (M_W 6,000) at 10%, 20%, 30%, 40%, 50% (by weight) based on the total weight of starch and PLA, and 30% PVOH at various molecular weights (M_W 6,000, 25,000, 78,000, and 125,000 dalton) were added to starch/PLA blends. PVOH interacted with starch. At proportions greater than 30%, PVOH form a continuous phase with starch. Tensile strength of the starch/PLA blends increased as PVOH concentration increased up to 40% and decreased as PVOH molecular weight increased. The increasing molecular weight of PVOH slightly affected water absorption, but increasing PVOH concentration to 40% or 50% increased water absorption. Effects of moisture content on the starch/PLA/PVOH blend also were explored. The blend containing gelatinized starch had higher tensile strength. However, gelatinized starch also resulted in increased water absorption.     

Miscibility and Biodegradability of Poly(Butylene Succinate)/Poly(Butylene Terephthalate) Blends

As one of the biodegradable polymers, the blend of poly(butylene succinate) and poly(butylene terephthalate) is dealt with in this study. In our previous work, it was demonstrated that PBS and PBT are immiscible not only from the changes of T _g but also from logG–log G plots. It is expected that the biodegradability of the blends could be improved by enhancing the miscibility. We tried to induce the transesterification reaction between two polyesters with various time intervals to enhance the miscibility of the blends. The extent of transesterification reaction was examined by ¹H-NMR. We utilized a dynamic mechanical thermal analyzer and a rotational rheometer to investigate the changes in miscibility. We also verified the biodegradability of PBS/PBT blends after the transesterification reaction by the composting method.     

Synthesis, Characterization, and Hydrolytic Degradation of Copolymers of 2-Methylene-1,3-dioxepane with Ethylene and with Styrene

2-Methylene-1,3-dioxepane (MDP) was copolymerized with ethylene (E) at a pressure of approximately 1000 psi and a temperature of approximately 70°C with AIBN as the free radical initiator. The copolymers obtained, poly(MDP-co-E), were characterized by elemental analysis, IR, ¹H-NMR and ¹³C-NMR spectroscopy, DSC, and GPC. The copolymers contained 2–15 mol% ester units. MDP was also copolymerized with styrene (S) at 120°C with di-t-butyl peroxide as the initiator to prepare the copolymer, poly(MDP-co-S). The number-average molecular weights of both types of copolymers were in the range of 6000 to 11,000, and the weight-average molecular weights were in the range of 9000 to 17,000. The melting temperatures of poly(MDP-co-E) decreased with increasing ester unit content in the copolymer. For the MDP-S copolymers, the glass transition temperatures decreased with increasing ester unit content. Both poly(MDP-co-E) and poly(MDP-co-S) were degraded by methanolysis, and their molecular weights decreased by the expected amounts based on the ester unit content.     

Biodegradable Poly(butylene succinate) and Poly(butylene adipate-co-terephthalate) Blends: Reactive Extrusion and Performance Evaluation

Two biodegradable polyesters, poly(butylene adipate-co-terephthalate) (PBAT) and poly(butylene succinate) (PBS) were melt-compounded in a twin screw extruder to fabricate a novel PBS/PBAT blend. The compatibility of the blend was attributed to the transesterification reaction that was confirmed by Fourier transform infrared spectroscopy. The Gibbs free energy equation was applied to explain the miscibility of the resulting blend. Dynamic mechanical analysis of the blends exhibits an intermediate tanδ peak compared to the individual components which suggests that the blend achieved compatibility. One of the key findings is that the tensile strength of the optimized blend is higher than each of the blended partner. Rheological properties revealed a strong shear-thinning tendency of the blend by the addition of PBAT into PBS. The phase morphology of the blends was observed through scanning electron microscopy, which revealed that phase separation occurred in the blends. The spherulite growth in the blends was highly influenced by the crystallization temperature and composition. In addition, the presence of a dispersed amorphous phase was found to be a hindrance to the spherulite growth, which was confirmed by polarizing optical microscopy. Furthermore, the increased crystallization ability of PBAT in the blend systems gives the blend a balanced thermal resistance property.     

Synthesis and Characterization of Bio-Based Amorphous Polyamide From Dimethyl furan-2,5-dicarboxylate

Journal of Polymers and the Environment - In this research, bio-based polyamide (bio-PA) was synthesized from dimethyl furan-2,5-dicarboxylate and 1,3-cyclohexanedimethanamine by melt...     

Natural Weathering of Polypropylene and Waste Tire Dust (PP/WTD) Blends

Three series of polypropylene and waste tire dust (PP/WTD) blends using three different WTD sizes were prepared, compression-molded and cut into dumbbells. The specimens were exposed to natural weathering in the northern part of Malaysia for a period of 6 months. The results show that at the same blend composition, blends with fine WTD size exhibit higher mechanical properties than that of blends with coarse WTD after exposure to natural weathering. Regardless of WTD size, the retention of tensile strength and elongation at break, E_b increases with the increase in WTD content. From the exposed surface morphology, it is apparent that the blends with fine WTD and WTD-rich blends were able to withstand weathering better than blends with coarse WTD and PP-rich blends. The DSC thermograms suggest that the overall drop in melting temperature (T_m) of the exposed blends decreases as the WTD content increases.