Oriented Polypropylene Tapes Research Articles

Development of drawn polypropylene-based blends and composites

We developed highly oriented polypropylene tapes with solid-state drawing, and studied the effect of additives—two grades of talc, low-density polyethylene (LDPE), and an amorphous poly-alpha-olefin (APAO). The PP compounds were prepared in a co-rotating twin-screw extruder, and sheet films were extruded. The specimens cut out from the sheet films were drawn in a tensile testing machine, and the drawing temperature of 130 °C was maintained by the heating chamber of the tensile testing machine. A draw ratio of λ=10 was set. We investigated the work of drawing and prepared DSC and tensile tests. Both types of talc acted as strong nucleating agents and increased the tensile strength and modulus of the tapes. APAO reduced the crystalline melting enthalpy only to a small extent. Both APAO and LDPE reduced the tensile strength and modulus and increased the strain at break of the tapes.

Nonlinear creep response of oriented polypropylene tapes

The creep response of a highly oriented polypropylene tape used for the manufacture of self-reinforced polypropylene or all-polypropylene composites was studied over a range of stresses and temperatures. Similar to oriented polyethylene, the creep compliance is linear viscoelastic at short loading times, whereas pronounced stress dependence is observed at longer loading times. A mathematical model is proposed, where the total deformation of the fibre is regarded as being composed of a stress-linear delayed elastic component and a nonlinear plastic flow contribution. Model predictions are in good agreement with the experimental data.

Calorimetric Investigations of Oriented Polypropylene Tapes and Self‐Reinforced Composites

SummaryDifferential scanning calorimetry (DSC) is a commonly applied method of determining various physical properties of thermoplastic polymers. Analyzing DSC melting and crystallization curves it is possible to verify whether the macromolecules orientation occurs in fibers, films and self‐reinforced polymer composites (SRC). This paper presents the comparison of the results of calorimetric investigations of polypropylene (PP) single polymer composites (SRC) with the investigations of constrained PP tape samples additionally annealed before the measurement. The program of thermal treatment resembled temperature changes in the mold during SRC production by hot compaction method. The results confirmed a substantial influence of compression molding pressure on the melting process of oriented PP reinforcement used in the production of single polymer composites.

Tensile behaviour of intralayer hybrid composites of carbon fibre and self-reinforced polypropylene

To improve the toughness of carbon fibre composites, unidirectional carbon fibre prepregs were hybridised with highly oriented polypropylene (PP) tapes. The latter tapes are used in self-reinforced PP composites (SRPPs) with high toughness, but relatively low stiffness. The tensile behaviour of intralayer hybrids of oriented PP tapes and CFPP prepreg tapes was investigated by changing the layup and weave pattern, and by adding interleaved PP films. While stiffness and strength of these hybrids was decreased compared to CFPP, their ductility significantly increased by adding oriented PP tapes. The parallel behaviour of the two constituent materials was caused by delaminations, which developed after the CFPP failure and spreads over the entire sample. This behaviour was modelled and proven to be independent of layup and weave pattern. Interleaved films, which are often necessary for thermoformability, limited the delamination development by increasing the interlayer bonding and yielded a lower ultimate failure strain.

The incorporation of carbon nanofibres to enhance the interlayer adhesion of hot compacted single-polymer polypropylene composites

The current work is a major extension of two very different studies carried out previously to investigate factors that affect the peel strength of single-polymer composites produced by the Leeds hot compaction process. First, it was found that the peel strength was significantly increased by introducing interleaved films, of the same polymer, between the layers of woven oriented tapes that make up the composite. Secondly, it was shown that incorporation of carbon nanofibres (CNF) into the oriented tapes prior to hot compaction could also increase peel strength.In the present study we have investigated the amalgamation of these two approaches, in particular to see if there are synergistic advantages in the combination. Samples were produced with and without interleaved films, and with and without carbon nanofibres, located either in the oriented polypropylene tapes, in the interleaved film or in both. Maximum peel strength was achieved with the combination of the interleaved film and the incorporated nanofibres, but importantly this could be achieved with the CNF located only in the film. This has significant processing and performance advantages as the incorporation of CNF into the oriented tapes tends to limit the drawability of the polypropylene due to internal voiding around the particles.Scanning electron micrographs of the hot compacted composites show a strong correlation between the observed damage on the peel surfaces and the measured peel loads. It is shown that the peel load is dependent on the fraction of melted matrix at the interface and hence the interleaved films give additional matrix material at this point. It is also shown that the incorporation of CNF promotes fibrillation, and so increases the amount of energy absorbed during peeling.

The effect of processing conditions on the mechanical properties and thermal stability of highly oriented PP tapes

It has previously been shown possible to use highly oriented polypropylene (PP) tapes to create self-reinforced (all-PP) composites. It is desirable to understand the relationship between tape processing parameters and the mechanical properties and thermal stability of the tapes, as these tape properties will govern the ultimate properties of the all-PP composite. In this paper, the effects of the tape drawing parameters such as draw ratio ( λ), drawing temperature and thermal annealing on the final mechanical properties, density and dimensional thermal stability of the tapes are presented. PP tapes drawn to λ = 17 possess tensile moduli of ∼15 GPa and tensile strengths of ∼450 MPa. PP tapes with high draw ratios, λ > 9.3, show a decrease in density, a change from transparent to opaque appearance and increased dimensional thermal stability with increasing draw ratio. The results of an investigation into the effects of a thermal annealing step, targeted at improving the dimensional thermal stability of these highly oriented PP tapes, are also presented.

Fatigue Properties of Highly Oriented Polypropylene Tapes and All-Polypropylene Composites

This paper describes the fatigue behaviour of newly developed all-polypropylene (all-PP) tapes and composites, with reference to the composite processing conditions, testing temperature and making a comparison with commercial alternatives. All-PP tapes are highly oriented and their failure behaviour follows that of other highly oriented polymers. All-PP woven composites fail ultimately due to PP tape failure. However, this failure mode is accompanied by delamination of fabrics in the woven structure. Consolidation pressure plays a decisive role in controlling the interlaminar properties and hence the delamination resistance and furthermore the fatigue limit of the composite. Comparison of all-PP woven composites with commercial alternatives based on glass and natural fibres reveals the excellent relative performance of all-PP composites under fatigue loads. Fatigue properties of all-PP composites are however sensitive to the testing temperature, and elevated temperatures can lead to a rapid reduction of the fatigue resistance of these all-polymer systems.

The effect of moderate pressure on the crystalline structure of oriented polypropylene tapes using in situ X‐ray diffraction

AbstractHighly oriented isotactic polypropylene tapes were examined under moderate pressure by heating and cooling during in situ X‐ray diffraction (XRD) measurements using synchrotron radiation. The formation of γ‐isotatic polypropylene (iPP) is observed upon recrystallization under pressure from the melt. The amount of γ‐iPP formed, as a function of pressure, exhibits a minimum at about 100 MPa. Upon applying moderate pressure (up to 60 MPa) significant changes are observed in the unit cell parameters, compared to their values at atmospheric pressure. At pressures above 60 MPa only a small decrease in the b unit cell parameter is observed. Copyright © 2007 John Wiley & Sons, Ltd.

The effect of temperature and strain rate on the mechanical properties of highly oriented polypropylene tapes and all-polypropylene composites

The creation of highly oriented, co-extruded polypropylene (PP) tapes allows the production of recyclable “all-polypropylene” (all-PP) composites, with a large temperature processing window and a high volume fraction of highly oriented PP (>90%). The wholly thermoplastic nature of these ‘self-reinforced’ composites implies that the mechanical performance may vary with temperature. This paper describes the mechanical performance of all-PP composites by measuring the mechanical properties of highly oriented PP tapes and subsequent all-PP composites at a range of temperatures by static and dynamic testing methods. The time–temperature equivalence of all-PP composites is investigated by creating mastercurves of dynamic modulus and tensile strength. A comparison of the performance of these composites with commercial glass fibre reinforced polypropylene composites is included.

Interfacial properties of highly oriented coextruded polypropylene tapes for the creation of recyclable all‐polypropylene composites

AbstractThe creation of highly oriented, coextruded polypropylene (PP) tapes allows the production of novel, wholly thermoplastic, recyclable “all‐polypropylene” (all‐PP) composites, which possess both a large temperature processing window (>30°C) and a high volume fraction of reinforcement phase (highly oriented PP tapes: >90%). This large processing window is achieved by using coextruded, highly drawn PP tapes. To achieve coherent all‐PP composites the interfacial characteristics following consolidation must be understood. This article investigates the interfacial characteristics of these coextruded tapes by using microcomposite models to create interfaces between tapes of varying draw ratios, drawing temperatures, skin/core ratios, and skin layer thicknesses. The tape drawing parameters are seen to control the interfacial properties in subsequent microcomposite models. The failure mode of these specimens, and hence bond strength, varies with consolidation temperature, and a model is proposed describing and explaining this behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 118–129, 2007

The hot compaction behaviour of woven oriented polypropylene fibres and tapes. II. Morphology of cloths before and after compaction

The morphology of woven oriented polypropylene tapes and fibres has been studied both before and after processing by hot compaction. In this technique bundles of oriented tapes or fibres are subjected to suitable conditions of temperature and pressure so that just sufficient of each tape or fibre is selectively melted; on cooling, this material recrystallizes to bind the whole structure together. Three different polymers were studied, woven into various individual weave styles, in relation to optimum processing conditions. The weave style, the adhesion between neighbouring interfaces after compaction and the direction of crack propagation along the neighbouring interfaces on peeling were examined leading to clear correlations between the observed morphology and mechanical peel strength data.

The influence of carbon black on properties of oriented polypropylene 3. Thermal degradation under applied stress

Extending previous studies of the effect of carbon black variables on thermal degradation of oriented polypropylene tapes, it has been shown that level of applied stress and characteristics of carbon black influence the thermal oxidative stability of polypropylene. In particular, retained breaking strain exhibits a higher sensitivity to levels of applied stress than other measurable parameters. No change in carbonyl index occurs throughout the exposures even up to rupture points. Crystallinity values obtained from FTIR crystallinity index measurements are shown to be more reliable than those obtained from DSC and confirm that the applied stress has an orienting effect during oven-ageing. Relative to unfilled tapes, low particle size and low structure appear to enhance oxidation resistance while increased volatiles content reduces oxidation resistance of filled tapes. Even so, all carbon black-filled tapes, especially at ultimate stress loadings >10% showed superior performance to unfilled analogues. These effects and that of black concentration are interpreted in terms of the possible physical and chemical changes occurring.

The influence of carbon black on properties of orientated polypropylene Part I Tensile and physical properties

A series of oriented polypropylene tapes each containing carbon black having defined properties and at a specified concentration were produced and tested for their tensile and physical behaviours at 20 and 130 °C. Tenacities at 20 °C decreased as carbon black concentration increased from 2.5 to 5% (w/w) and with increasing particle size. At constant particle size and concentrations, tape tenacities were also inversely dependant on carbon black structure. The observed effects were expressed in terms of occlusion of polymer within carbon black aggregates having high structures thereby increasing the pigment particles effective volumes. When tested at 130 °C, variation in tape tenacities were less, probably as a consequence of the reordering effects of annealing. DSC and IR measures of crystallinity showed that the presence of carbon black and variations in particle properties influenced the character of the crystalline regions.

Influence of Waste Polymer Inclusion on the Performance of Oriented Polypropylene Geotextile Tapes

Part I of this series demonstrated the effects of recycled polymer inclusion on the tensile properties of oriented polypropylene tapes. Part II describes the effects of re cycled waste on structure and morphology. Under constant conditions of tape extrusion and drawing, the IR crystallinity of orientated tape shows a U-shaped relationship with waste concentration. There is a sudden drop of crystallinity at low waste concentration, which passes through a minimum with increasing waste content, and then gradually rises to the lower crystallinity value of the tape containing 100% waste. Sonic modulus and birefringence values decrease with increasing waste concentration. These changes in tape crystallinity and orientation, along with decreasing molecular weight, explain the loss of tape tenacity owing to the introduction of waste polymer during extrusion. Improved molecular orientation is evident in the presence of additional antioxidant stabilizer, because polymer chain degradation during processing is reduced.

Influence of Waste Polymer Inclusion on the Performance of Oriented Polypropylene Geotextile Tapes

Changes occurring in the tensile properties of oriented polypropylene tapes have been investigated following the addition of recycled process waste at various concen trations. In addition, the effects on resulting tape properties of adding stabilizers to blends of virgin polymer and waste prior to extrusion are determined. A significant loss in tape strength occurs when recycled or waste polypropylene is added because of thermooxidative degradation, as indicated by MFI and GPC studies. Our results demonstrate that useful tapes with acceptable tenacities in excess of 0.5 Ntex-1 can be achieved using up to 25% w/w of some recycled waste polymers in the absence of stabilizers. However, simultaneous introduction of a specified antioxidant system per mits waste polymer additions as high as 75% while maintaining acceptable tensile properties.

The effects of stress, environment and polymer variables on the durabilities of oriented polypropylene tapes

The combined roles of temperature, applied stress, relative humidity and exposure time have been investigated with respect to the degradation and changes in properties of a selection of oriented polypropylene tapes. Tapes were studied, having a range of average molecular weights and antioxidant types and one commercial sample contained carbon black. After ageing under ambient and elevated temperatures (90–130°C) and selected loads, for periods up to and including their failure, tapes were analysed for changes in tensile physico-chemical and thermal analytical property changes. Results are explained in terms of oxidative scission of polymer chains, which caused subsequent physical structural reorganisation. While application of low and medium stresses had little effect on these changes, stresses above 10% breaking stress seriously enhanced physico-chemical deterioration and shortened the times-to-failure. The effects of relative humidity were similar to those of increased temperature in that rates of degradation were enhanced. The presence of carbon black reduced stress sensitivity of tapes to degradation when loaded below 10% stress levels, and improved creep resistance, but showed poorer ageing performance at higher stress levels.