Properties Of Polypropylene Films Research Articles

Changes of Mechanical and Chemical Properties of PP and PC Films Due to UV-Light-Induced Degradation.

It is well known that sunlight induces the ultraviolet (UV) degradation of polymers. This paper describes the effects of UV irradiation on the change of mechanical properties of polypropylene (PP)and polycarbonate (PC) films. After the specimens were exposed to UV light from the fluorescent UV apparatus, some specimens were subjected to a dead load afterwards the exposures. Tensile tests and dynamic viscoelastic mechanical tests were conducted. In addition, infrared spectrum and molecular weight were measured in order to investigate changes in chemical properties. (1) The degradation of mechanical properties due to UV irradiation is divided into two periods, i. e., the degradation-incubation period and degradation-development period. The failure strain does not change in the first period, and gradually decreases with increase of the integrated UV irradiation energy. The applied stress during irradiation has a tendency to accelerate degradation. (2) The temperature during exposure influences degradation considerably when it is greater than the glass transition temperature. (3) The reason for the existence of the incubation period is different for two materials. PP has no active bases originally for light-induced chemical reaction, and thus a certain period is necessary to initiate scission of main chains. On the other hand, PC has active bases but the second conjugation is strong. Therefore a certain number of main chain scissions are required to decrease the failure strain.

Combined processing of polypropylene film by coextrusion and zone‐annealing

AbstractIn order to improve the mechanical properties of polypropylene film, a new processing combining extrusion and zone‐annealing has been applied. It was found that there are suitable conditions for each step in the combined processing. When the coextrusion draw ratio was low, the total draw ratio and modulus could be increased by the zone‐annealing subsequently done. The highest modulus was obtained when the film was coextruded at extrusion draw ratio 4 and then zone‐annealed at 120°C under 7 kg/mm2. The value was 12 GPa in Young's modulus or 17 GPa in dynamic modulus. The peak temperature of αc dynamic dispersion for the combinedly processed film was 109°C, which is higher by 10°C than that for the as‐coextruded film. Four drawing methods were compared in dynamic viscoelasticity. These methods are the coextrusion, zone‐drawing/zone‐annealing, two‐step coextrusion, and the combined processing by coextrusion and zone‐annealing. The highest dynamic modulus for each method was arranged in the above order. The combined processing indicated the most effective improvement in mechanical properties, because it is believed that lamellae in the original film were broken by cooperating interaction of shear stress, compression, and tension on coextrusion and then the superstructure with a high crystallinity and a high molecular orientation was formed on zone‐annealing.

Crosslink Enhancement in Polypropylene Film by Gamma Irradiation in the Presence of Acetylene

The effects of crosslink enhancement by the presence of acetylene during gamma irradiation, on the physical and mechanical properties of polypropylene film are reported. Gel contents show that crosslink enhancement is considerably greater if the sample is highly annealed (PPA) than if it is quenched (PPQ). For PPA, thermal analysis suggests only minor damage to the crystalline lamellae, but significant stabilisation of lamellae by crosslink formation in the lamellar surface regions. This is supported by an increased resistance to the yielding process observed in tensile stress/strain and creep tests. The effects in PPQ is less.

Investigation of the structure and physicomechanical properties of polypropylene film

The authors have investigated the effect of the dynamic degree of crystallinity, stereoisomeric composition, intrinsic viscosity, and other factors on the nature of the structure formed when polypropylene is made into film and on the physicomechanical properties of the film.

Structure–property relationships for liquid transport in modified polypropylene membranes

AbstractIn view of the intensifying interest in the application of polymeric membranes in mixture separation processes, the permeation and permselective properties of polypropylene films toward several candidate organic liquids and vapors were investigated. Polymer films were subjected to solvent and thermal treatments, and the effects of these treatments on film morphology and transport properties were studied. Structure–property relationships for membrane permeation were then developed. Polypropylene films were found to be selective toward toluene, relative to isooctane, and p‐xylene relative to o‐xylene. Liquid flux rates were found to depend primarily upon the solubility of the permeants in the films and the absolute difference in the solubility parameters of the polymer–liquid pair provided a good basis for correlation of this effect. Considering liquids of closely similar solubility parameters, fluxes were found to be dependent upon the apparent molecular cross sections of the permeants. Films annealed in various organic solvents at temperatures of 60–100°C exhibited enhanced permeability, with up to fifteenfold increase relative to untreated membranes, but with reduced selectivity towards the permeants. A mechanism to account for these effects through consideration of the influence of treating solvent type on polymer morphology is proposed. It postulates the formation of more open or coarser spherulitic structures as a result of recrystallization in the presence of solvent during annealing. The enhanced flux rates in the treated films are attributed to the changes in the spherulite textures and to diminished intercrystalline tie chain constrainment within the spherulitic substructure.

The dielectric properties of polypropylene with different macromolecular structure

TH~ dielectric properties of polymers are determined by the mobility of individual groups or of whole parts of the macromolecules, these properties reflecting changes in the aggregate state or state of phase. I t was stated in a series of recent papers, tha t the dielectric method could be sensitive to changes of supermolecular structure [1-4], but this aspect had not been examined to any extent. The purpose of the work reported here was to clarify the influence of supermolecular structural changes on the dielectric properties of polypropylene (PP) of trade name Moplen. This polymer had been selected because it permitted to produce PP samples of a certain structure [5], and also because some data on its dielectric properties were available [6-9]. PP films were produced by press-moulding at 10 kg/cm 2 from the melt at 200°C; the holding time of the melt was 30 rain. The films were then placed in a thermostat at T¢r=134°C for 4 hr (sample 1) or 15 min (sample 2), after which they were annealed.