Mechanical property and molecular weight distribution changes with photo- and chemical-degradation on LDPE films

In order to clarify the effect of photo- and chemical-degradation on the structure of polyethylene materials, the change in molecular weight distribution and mechanical properties of photo- and chemical-degraded LDPE films were investigated. The molecular weight distribution was significantly changed with photo-exposing times, and the drastic change appeared especially for 8 days-exposed samples where the molecular weight of the high molecular weight fraction increased. However, the molecular weight of the lower molecular weight fraction was almost the same for all the photo-exposed films, irrespective of irradiation time, and also for chemical-degraded films. It is suggested that the molecular chains with a certain length, which consist of a crystal lamellae in spherulites, cannot be broken by photo-irradiation. Consequently, there would be threshold for the molecular weight in terms of photo-degradation process, and almost the same threshold can be observed for the chemical-etching films. Stress-strain curves were measured for photo-degraded films and their “quenched films after remolding” and “annealed films after remolding”, and chemical-degraded films.     

Synthesis,Characterization and Application of Poly(lactic-co-glycolic acid) with a Mass Ratio of Lactic to Glycolic Segments of 52/48

Poly(lactic-co-glycolic acid)(PLGA) is one of the most representative degradable copolymers and promising drug carriers. In the current paper, the PLGAs with a lactic acid/ glycolic acid(LA/GA) molar ratio of 52/48 and various molecular weights were prepared by a melting method. The molecular weight, molecular weight distribution, and thermal stability were determined by ¹H NMR and thermogravimetric analysis methods. The results demonstrated that PLGAs with the fixed LA/GA molar ratio(52/48), different molecular weights, and narrow molecular weight distribution could be obtained by solely altering the reaction time. The PLGA films were prepared, and their properties including micro-structure, mechanical property, in-vitro cytotoxicity, and biodegradability were characterized. In combination with the homogeneous microstructures and mechanical properties, the drug-loading and releasing properties of PLGA_3.2 films were investigated. The results show that PLGA_3.2 film with an LA/GA molar ratio of 52/48 is a promising curcumin carrier.     

脂肪族水性聚氨酯的力学性能研究

考察了软段的种类、分子量大小、混合软段的组成对产物力学性能的影响作用。同时还研究了二羟甲基丙酸(DMPA)用量以及中和剂的影响作用．实验结果表明。软段结构对脂肪族水性聚氨酯成膜的力学性能影响很大，聚酯型产物具有较高的模量和拉伸强度。聚醚型产物则具有较高的伸长率．混合软段对产物力学性能的影响较为复杂，随着软段中聚醚含量的升高，产物的硬度和模量均大幅度下降，但拉伸强度和伸长率的变化并不是一个线性关系．产物的模量随软段分子量的提高而降低，但伸长率和拉伸强度却有所提高．当DMPA用量较高时。产物的模量和拉伸强度均较高：当DMPA用量较低时，产物则具有较高的伸长率．中和剂的种类对产物力学性能的影响明显，当以NaOH为中和剂时，产物具有较高的硬度、模量、拉伸强度：以三乙胺为中和剂时，产物具有较高的伸长率．     

Effect of Molecular Weight of WPU on the Heterogenic PUA Composite Latex Prepared by Soap-Free Emulsion Polymerization

Aqueous acrylic-polyurethane (PUA) composite emulsion was prepared by soap-free seeded emulsion copolymerization. Waterborne polyurethane (WPU) was used as the seeded emulsion and functioned as surfactant. The effect of molecular weight of WPU on the heterogenic was investigated. The molecular weight of WPU was controlled by varying the NCO/OH mole ratio. The GPC results confirmed that the molecular weight of WPU presented double distribution. And the molecular weight of WPU decreased with the increasing NCO/OH mole ratio. Surface tension test indicated that the molecular weight had little influence on the surface activity of WPU. However, after emulsion copolymerization of acrylic monomers, the morphology and properties of the PUA composite were impacted markedly by the molecular weight of WPU. With an increase in the NCO/OH mole ratio, the morphology of PUA composite latex changed from core-shell structures to fish bowl structure, and the mechanical properties of PUA films changed correspondingly.     

Effects of initial morphology and molecular weight on the deformability of poly(ethylene terephthalate)

Solution-grown crystal (SGC) mats and solution-cast (SC) films of poly(ethylene terephthalate) (PET) were drawn by solid-state coextrusion followed by tensile drawing of the coextrudates. Drawabilities and properties of the drawn films, such as mechanical and thermal properties, were investigated as functions of molecular weight, initial morphology, and drawing conditions. The initial morphology and molecular weight have a marked effect on the drawability and tensile properties of the resultant drawn films. The attainable maximum draw ratio increases with increasing molecular weight, and the highest draw ratio of 11.5 can be achieved by two-stage drawing of SC films prepared from pellets with an intrinsic viscosity of 1.43 dl/g. Such highly drawn films exhibit a tensile modulus of 17.5 GPa and strength at break of 400 MPa. These values are comparable to those obtained in conventional spinning of standard grade PET. At a given draw ratio, the tensile strength of the drawn films increases with increasing molecular weight, but the molecular weight dependence is not so marked in the tensile modulus as in the tensile strength. At a given molecular weight, the drawability of SGC mats is lower than that for SC films; however, the efficiency of drawing is higher for the former than for the latter. The difference may arise from the difference in crystallinity and/or crystal perfection of predrawn samples.     

Formulation and Characterization of Nicotine Microemulsion-Loaded Fast-Dissolving Films for Smoking Cessation

The present study aimed to develop a nicotine microemulsion (NCT-ME) and incorporate it into a fast-dissolving film. The NCT-ME was prepared by mixing the specified proportions of nicotine (NCT), surfactant, co-solvent, and water. The NCT-ME was measured by its average droplet size, size distribution, zeta potential, and morphology. NCT-ME fast-dissolving films were prepared by the solvent casting technique. The films were characterized by morphology, weight, thickness, disintegration time, and mechanical strength properties and the determined NCT loading efficiency and in vitro drug release. The results showed that almost all NCT-MEs presented droplet sizes of less than 100 nm with a spherical form, narrow size distribution, and zeta potentials of −10.6 to −73.7 mV. There was no difference in weight and thickness between all NCT-ME films, but significant changes in the disintegration times were noticed in NCT40-Smix[PEG-40H(2:1)]10 film. The mechanical properties of films varied with changes in type of surfactant. About 80% of the drug release was observed to be between 3 and 30 min. The drug release kinetics were fitted with the Higuchi matrix model. The NCT40-Smix[P-80(1:1)]10 film showed the highest dissolution rate. It was concluded that the developed ME-loaded fast-dissolving film can increase drug release to a greater extent than the films without ME.     

Mechanical properties of solvolysis lignin-derived polyurethanes

In order to study the tensile properties of solvolysis lignin polyurethanes, polyurethane (PU) films were prepared from the solvolysis lignin (SL)–polyethylene glycol (PEG)–diphenylmethane diisocyanate (MDI) system, and in addition to this further PU films were also prepared from the SL–MDI system. In the SL–PEG-MDI system, the SL content, the molecular weight of PEG and the NCO:OH ratio were varied in order to control the physical properties. The tensile stress and Young's modulus of the PUs of the SL–PEG–MDI type increased with increasing SL content and NCO:OH ratio. The tensile properties of the PUs from the SL–MDI system showed no NCO:OH ratio dependency; i.e. the mechanical properties of PUs are not influenced by the change in crosslinking. It is possible to control the tensile properties of PUs of the SL–PEG–MDI type by changing the content of PEG and SL at a constant NCO:OH ratio.     

Preparation of Meltable Aromatic Polyimides and Their Adhesive Properties

A series of molecular-weight-controlled aromatic polyimides based on 4,4′-oxydiphthalic anhydride (ODPA), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 3,3′-diaminodiphenylsulfone (3,3′-DDS) were synthesized in the presence of phthalic anhydride (PA) as an end-capping agent. The effect of molecular weight on the solubility, melt viscosity, thermal and mechanical properties of the polyimides was investigated. Experimental results demonstrated that the polyimides exhibit good solubility in most polar aprotic solvents and in some common organic solvents, such as DMSO and THF. Homogeneous and stable polyimide solutions with solid contents as high as 40–45 wt% were prepared. High-quality polyimide films were obtained by casting the polyimide solutions onto glass plates and baking them at a relatively low temperature. The polyimide films exhibited outstanding thermal and mechanical properties. The rheological behavior of the polyimides depends on their molecular weight. The adhesive properties of polyimide films bonded to stainless steel at different temperatures were evaluated by the lap shear strength (LSS) test. The polyimides with moderate molecular weight exhibited better adhesive properties. The LSS of polyimide films at ambient and elevated temperatures increased with increasing bonding temperature, which is attributed to the better flow and wetting of the polymer melts during the bonding process.     

ELECTRICAL AND MECHANICAL PROPERTIES OF POLYANILINE FILMS——EFFECT OF NEUTRAL SALTS ADDED DURING POLYMERIZATION*

The electrical and mechanical properties of polyaniline (PANI) films syn-thesized by the presence of the selected neutral salts in the polymerization were measuredas a function of the properties and the concentration of the selected neutral salts, andthe protonation state. It was found that both the electrical and mechanical properties ofPANI films were enhanced by adding neutral salts in the polymerization. The adding ofthe neutral salts in the polymerization resulted in extended conformation of polymer chainand increasing of molecular weight of PANI, which may be the reasons why the electricaland mechanical properties of PANI films were improved by the presence of neutral salts inthe polymerization.     

Properties of acrylic–polyurethane hybrid emulsions synthesized by the semibatch emulsion copolymerization of acrylates using different polyurethane particles

Aqueous acrylic–polyurethane hybrid emulsions were prepared by the semibatch emulsion copolymerization of methyl methacrylate and butyl acrylate in the presence of eight polyurethane dispersions. The polyurethane dispersions were synthesized with isophorone diisocyanate, 1000 and 2000 molecular weight polyester polyols, 1000 molecular weight polyether polyol, butanediol, and dimethylol propionic acid. Acrylic monomers were added in the monomer emulsion feed. We studied the effect of the use of different polyurethane seed particles and the effect of different weight ratios of methyl methacrylate to butyl acrylate on the emulsion properties, microphase structure, and mechanical properties of hybrid films. The average particle size and distribution were determined by photon correlation spectroscopy. The rheological properties of polyurethane dispersions and hybrid emulsions were tested under destructive conditions by an examination of flow curves and under nondestructive conditions of oscillatory shear in a range of linear viscoelastic responses. Differential scanning calorimetry was performed to characterize the thermal‐response properties of polymeric films. The relative average molecular weights were determined by gel permeation chromatography. The interactions between the acrylic and polyurethane components in hybrid particles and particle structure were studied with infrared spectroscopy and nuclear magnetic resonance spectroscopy. Mechanical properties such as the Koenig hardness, tensile strength, elongation at break, and Young's modulus were measured. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4050–4069, 2005     

Solid state characterization of the structure of chitosan films

Films of chitosan, prepared by different fabrication processes, were examined at several structural levels, from the molecular to the macroscopic. This revealed the presence of polymorphic crystal forms, which varied with film treatment. Similarly, morphological structures varying from spherulites to rods were formed, depending on film processing conditions. The effect of structure on the mechanical properties, as well as the orientability of the films, were also investigated.     

Synthesis and characterization of semicrystalline cycloaliphatic polyester/poly(dimethylsiloxane) segmented copolymers

High molecular weight poly(dimethylsiloxane)/semicrystalline cycloaliphatic polyester segmented copolymers based on dimethyl-1,4-cyclohexane dicarboxylate were prepared and characterized. The copolymers were synthesized using a high trans content isomer that afforded semicrystalline morphologies. Aminopropyl-terminated poly(dimethylsiloxane) (PDMS) oligomers of controlled molecular weight were synthesized, end capped with excess diester to form a diester-terminated oligomer, and incorporated via melt transesterification step reaction copolymerization. The molecular weight of the polysiloxane and chemical composition of the copolymer were systematically varied. The polysiloxane segment was efficiently incorporated into the copolymers via an amide link and its structure was unaffected by low concentrations of titanate transesterification catalyst, as shown by control melt experiments. The homopolymer and copolymers were characterized by solution, thermal, mechanical, and surface techniques. The segmented copolymers were microphase separated as determined by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and by transmission electron microscopy (TEM). It was demonstrated that relatively short poly(dimethylsiloxane) segment lengths and compositions were required to maintain single phase melt polymerization conditions. This was, in fact, the key to the successful preparation of these materials. The copolymers derived from short poly(dimethylsiloxane) segments demonstrated good mechanical properties, melt viscosities representative of single phase polymer melts, and were easily compression molded into films. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3495–3506, 1997     

A biobased aliphatic polyester derived from 10-hydroxydecanoic acid: Molecular weight dependence of physical properties

Poly(10-hydroxydecanoate) (PHDA) is of interest as a new-type aliphatic polyester due to its bioresource and flexible mechanical property. A series of PHDAs with varied molecular weights (M_n from 27 kg/mol to 74 kg/mol) were prepared by optimized melt polycondensation of 10-hydroxydecanoic acid (HDA). Through DSC, WAXD, POM and tensile tests, the effects of molecular weight on the physical properties, including thermal properties, crystallization behavior, crystal morphology, rheological behavior and mechanical properties of PHDA were studied in detail. The results demonstrated that the physical properties of PHDA largely rely on the molecular weight. In particular, the brittle-ductile transition of PHDA occurred when the molecular weight increased up to 55 kg/mol. With the increase of molecular weight, the elongation at break was largely improved and finally exceeded 1400%. The ultimate tensile strength kept about 20 MPa. Hence, PHDA has a PE-like mechanical property. Our work highlights that PHDA is a polymer with excellent performance, which provides an alternative to durable petroleum resourced packaging materials.     

Fractionation of Regenerated Silk Fibroin and Characterization of the Fractions

The molecular weight (MW) of regenerated silk fibroin (RSF) decreases during degumming and dissolving processes. Although MW and the MW distribution generally affect polymer material processability and properties, few reports have described studies examining the influences of MW and the distribution on silk fibroin (SF) material. To prepare different MW SF fractions, the appropriate conditions for fractionation of RSF by ammonium sulfate (AS) precipitation process were investigated. The MW and the distribution of each fraction were found using gel permeation chromatography (GPC) and SDS-polyacrylamide electrophoresis (SDS-PAGE). After films of the fractionated SFs formed, the secondary structure, surface properties, and cell proliferation of films were evaluated. Nanofiber nonwoven mats and 3D porous sponges were fabricated using the fractionated SF aqueous solution. Then, their structures and mechanical properties were analyzed. The results showed AS precipitation using a dialysis membrane at low temperature to be a suitable fractionation method for RSF. Moreover, MW affects the nanofiber and sponge morphology and mechanical properties, although no influence of MW was observed on the secondary structure or crystallinity of the fabricated materials.     

Synthesis of Poly(1,3-cyclohexadiene) Containing Star-Shaped Elastomers

The synthesis of high molecular weight star-shaped polymers comprising poly(1,3-cyclohexadiene-block-isoprene) diblock arms coupled to a divinyl benzene (DVB) core is reported. The number average molecular weights of the diblock arms were varied from 30000 to 50000 and the ratio of DVB to n-butyllithium (nBuLi) was systematically varied from 3:1 to 12:1. Size exclusion chromatography coupled with light scattering detection was utilized to detect the formation of star-shaped polymers and the presence of star-star coupling. The molecular weight distribution (<M_w>/<M_n>) of the star polymers ranged from 1.25 to 1.50. The effect of poly(1,3-cyclohexadiene) content on the mechanical properties of these novel elastomers is reported. The elastic modulus, elongation at break, and tensile strength of these elastomers were all found to be a function of the percentage of poly(1,3-cyclohexadiene). The glass transition temperatures were determined using both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Atomic force microscopy was performed in the tapping mode (TMAFM) to verify the presence of microphase separation.     

Aromatic copolyimide–amides II

Six thermally stable polyimide-co-amides have been synthesized from sulfurylbis[N-(4′-phenylene)-4-(chloroformyl)-phthalimide] and various aromatic diamines. Linear, high molecular weight final polymers were obtained by one step low-temperature solution condensations in dimethylacetamide. Thermal properties such as glass transition and polymer decomposition temperatures and solution properties such as viscosities and solubilities varied significantly with polymer structure. Tough, flexible films of these polymers were cast from solution. The thermal-oxidative stabilities of films were strongly dependent on structure, solvents used, and impurities present.     

Viscoelastic properties of heterogeneous network polymers from poly(D-glutamic acid) and poly(oxyethylene glycol)

A series of five heterogeneous network polymers was prepared from poly(D -glutamic acid) (PDG) and poly(oxyethylene glycol) (PEG), and their dynamic mechanical properties were studied. The content of PDG was fixed at 60% by weight, and the molecular weight of PEG was changed to obtain networks with various crosslink densities. An increase in the PEG molecular weight from 330 to 880 caused considerable broadening of tan δ and E″ curves, and peak temperatures for tan δ and E″ decreased slightly. Curves of tan δ and E″ for PDG–PEG 4000 (indicating a PEG component of molecular weight 4,000) were much broader and the existence of two peaks was recognized. These findings and x-ray photographs suggest that PDG–PEG 330, 570, and 880 give films of fairly uniform phase, but that PDG–PEG 1830 and 4000 give films with two-phase structure. The factors influencing the dynamic mechanical properties in decreasing order of effectiveness are found to be the proportions by weight of PDG and PEG, the compatibility of PDG with PEG, the crosslink density, and the concentration of free carboxyl groups. The infrared spectra of these polymers indicate that at least part of the PDG component retains the α-helix conformation.     

Evaluation of methoxy polyethylene glycol‐polylactide diblock copolymers as additive in hypromellose film coating

This paper deals with a new application of diblock methoxy polyethylene glycol‐polylactide block copolymers, a class of synthetic biomaterials largely studied in the pharmaceutical and biomedical fields owing to their favorable properties such as biocompatibility, biodegradability, low immunogenicity, and good mechanical properties. In this work, these materials were evaluated as additives for gastro‐soluble pharmaceutical coating aimed to reduce film stiffness and water permeability. Two copolymers with different polylactide chain lengths were synthesized and characterized in term of molecular weight and solid‐state properties. A series of free films with different hypromellose/copolymers ratio were prepared and characterized in terms of appearance, components miscibility, plasticity, and water vapor permeability. The obtained results demonstrate that copolymers effectively influence hypromellose film properties according to their concentration and molecular weight. Specifically, the addition of the copolymer with a molecular weight of 6.5 kDa in a ratio hypromellose:polymer 5:1, allowed to obtain films with good appearance, improved plasticization, and water permeability properties. For higher molecular weight, copolymer or different ratios was not possible to observe the improvement of all the properties at the same time. The results also make possible to define the critical features to improve in order to use block copolymers as additive in hypromellose film coating. The availability of new water‐soluble additives able to work as plasticizer and moisture sealer in polymeric films represents an important progress not only in the field of pharmaceutical coating but also in that of food coatings, as for example in the formulation of edible films. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn,ultrahigh-molecular-weight polyethylene cast from solution. II. Drawability and mechanical properties

The effect of molecular weight distribution (MWD) on the ultradrawability and mechanical properties of solution-cast films of ultrahigh-molecular-weight polyethylene (UHMW-PE) has been investigated using tensile and dynamic mechanical measurements. The MWD has a marked effect on ultradrawability and thus on the ultimate mechanical properties such as the tensile modulus. It is proposed that UHMW-PE with a narrow MWD(N-PE) attains the ultimate structure at a lower draw ratio than UHMW-PE with a broad MWD(B-PE) because of the existence in the latter of less fully extended intercrystalline tie chains. It is found that, at the same drawing temperature (100°C), N-PE shows a higher modulus than B-PE at draw ratios up to 150 x, which is assumed to be the ultimate value for N-PE.     

Synthesis of hydroxyl-terminated polybutadiene possessing high content of 1,4-units via anionic polymerization

<正>The hydroxyl-terminated polybutadiene(HTPB) possessing high content of 1,4-units was synthesized by anionic polymerization of butadiene,using alkyllithium containing silicon-protected hydroxyl group as initiator and cyclohexane as solvent.The polymers were characterized by GPC,IR and ~1H-NMR.The mechanical properties of cured films were also evaluated.The results show that the content of 1,4-units for HTPBs made by anionic polymerization reaches up to 90%.The molecular weight distribution is very narrow(≤1.05).The functionality of hydroxyl groups approaches 2.Compared with free radical HTPB,the elongation at break of anionic HTPB films increased by 70%,while the tensile strength remained nearly unchanged.This new HTPB can be very useful in solid propellant.