Melt miscibility of blends of isotactic polypropylene and homogeneous iso-propylene-1-hexene copolymers

2016

Polymer

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The mechanical properties of binary blends of propylene-1-hexene random copolymers (with 11 and 21 mol% 1-hexene) are studied in parallel with polymorphic transformations under uniaxial tensile deformation. The modulus, yield stress, and draw ratio of the pure PH copolymers decrease with increasing 1-hexene content, while for the blends the change of mechanical properties with composition is highly non-linear. The addition of just 10 wt % PH11 to PH21 doubles the elastic modulus and yield strength of the blends in reference to the value of PH21, reaching for all blends values close to the performance of pure PH11. The elongation at break and the ultimate tensile strength increase more gradually with content of PH11. On tensile deformation, pure components and blends undergo morphological and polymorphic transformations, such as a reversible lamellar to fibrillar transformation of trigonal PH21, or an irreversible α crystal to mesophase in pure PH11 and the blends. In blends and neat PH11, a fibrillar trigonal morphology that develops under deformation is stabilized by the transformation of α to mesophase, and remains after removing the load, explaining the lower elastic recovery of the blends compared to PH21. The formation of stress-induced trigonal crystallites in PH11 and blends after strains > 150% is explained as a decrease of the free energy barrier for nucleation of a phase that requires short iPP sequences.

Section: Introductionmentioning

confidence: 99%

Mechanical properties and stress-induced polymorphic transformations of blends of random isotactic propylene-1-hexene copolymers

Janani

2016

Polymer

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“…It has been reported that melts of binary blends of i PP with random propylene ethylene copolymers are immiscible in concentrations of comonomer higher than 15 mol% . The IPC are heterophasic materials because the ethylene content in the EPR component is around 50 mol%, as seen in Table .…”

Section: Resultsmentioning

confidence: 96%

Characterization and Morphological Distribution of Ethylene Content in Impact Propylene Copolymers

Santonja-Blasco

Rungswang

Macromolecular Symposia

2018

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The effect of ethylene content, in a range between 8 and 11 mol%, and distribution on the solid-state morphology of five impact polypropylene copolymers (IPC) have been studied via SEM, fractionation and microstructural characterization via gel permeation chromatography (GPC), hightemperature thermal-gradient interaction chromatography (HT-TGIC), and differential scanning calorimetry (DSC). All copolymers display heterophasic morphology, with rubbery droplets randomly distributed in a predominant iPP matrix. While the mass fraction of amorphous ethylene-propylene rubber molecules is very similar for all IPC studied, the size of the droplets increases from 0.6 to 1.1 μm with increasing ethylene content. This change in droplet size is correlated with changes in the composition of the crystalline ethylenepropylene (CEP) component extracted via fractionation.

“…Mixtures of iPP and propylene‐1‐alkene thermoplastic elastomers, form both miscible, and immiscible (but compatible) blends . In binary blends of random atactic propylene‐butene (PB) copolymers analyzed by SANS, the melt‐miscibility increased with increasing difference in content of 1‐butene .…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, in our recent work on melt miscibility of iPP and PH copolymers we estimated a critical value of difference in 1‐hexene content for miscibility of propylene 1‐hexene copolymers of about 11 mol%. This value is close to the critical value found for miscibility of iPP/PE blends …”

Section: Introductionmentioning

confidence: 99%

“…The ability of incorporating the branches in the trigonal crystalline regions of propylene 1‐hexene copolymers (with >13 mol% 1‐hexene) opens the window to study the effect of the trigonal phase on blends of iPP and copolymers of iPP with 1‐hexene . In an earlier study, we found that blends of iPP and PH11 are miscible in the melt in the whole range of compositions . Conversely, blends of iPP and PH21 are immiscible but partially compatible.…”

Section: Introductionmentioning

confidence: 99%

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Effect of melt miscibility, polymorphism, and crystal morphology on tensile deformation of blends of isotactic polypropylene and propylene‐1‐hexene random copolymers

Janani

Polymer Crystallization

2020

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The ductile behavior of isotactic polypropylene (iPP) can be effectively increased by blending with small contents (<25%) of a random propylene 1-hexene copolymer (PH). In this work, we have studied the uniaxial tensile deformation of binary blends of iPP with PH copolymers with 11 or 21 mol% 1-hexene. Blends iPP/PH11 are melt-miscible in the whole range of composition while iPP/PH21 blends are meltimmiscible, but partially compatible. On cooling, the lamellar morphology of each type of blend differs accordingly, and impacts their mechanical deformation. Miscible iPP/PH11 blends develop inter-mixed monoclinic lamellar stacks interconnected by tie molecules of iPP and PH admixed in the amorphous phase. During deformation, the monoclinic crystals transform to oriented mesophase at low strains due to effective stress transfer through the interconnected topology. These blends display the largest strain (~800%) and low recovery. Conversely, immiscible iPP/PH21 develop a coarser morphology of monoclinic and trigonal crystallites in the iPP-rich and PH21-rich domains, respectively. Less effective stress transfer associated with the coarse iPP/PH21 morphology leads to a delayed onset of orientation and a less effective monoclinic-mesophase transformation. The PH21 trigonal crystals of the blend orient but do not undergo polymorphic transformation. At high elongations fibrillar strain-induced trigonal crystals, provide a network of stable physical junction points that relax to the random orientation upon removal of the load, thus enhancing the elastic recovery of iPP/PH21 blends. K E Y W O R D S iPP copolymers, iPP crystallization, iPP mechanical properties, iPP polymorphism 1 | INTRODUCTION The polymorphic behavior, semicrystalline structure, and mechanical properties of isotactic poly(propylene) (iPP) change when defects or a comonomer are incorporated to the chain. The addition of a suitable content of comonomer to the iPP chain enables polypropylene materials with a wide spectrum of properties ranging from rigid thermoplastics to elasto-plastomers or to elastomers. [1]Mixtures of iPP and propylene-1-alkene thermoplastic elastomers, form both miscible, and immiscible (but compatible) blends. [2][3][4] In binary blends of random atactic propylene-butene (PB) copolymers analyzed by SANS, the melt-miscibility increased with increasing difference in content of 1-butene. [5] This effect was attributed to a negative enthalpy interaction between propylene and 1-butene monomer units and to attractive entropic contributions. Based on such results, it was hypothesized that the branches longer than ethyl,