Relationship between molecular structure, crystallization behavior, and mechanical properties of long chain branching polypropylene

Long-chain branching (LCB) is known as a suitable method to increase the melt strength behavior of linear polypropylene (PP), which is a fundamental weakness of this material. This enables the modification of various properties of PP, which can then be used—in the case of PP recyclates—as a practical “upcycling” method. In this study, the effect of five different peroxides and their effectiveness in building LCB as well as the obtained mechanical properties were studied. A single screw extruder at different temperatures (180 and 240 °C) was used, and long-chain branched polypropylene (PP-LCB) was prepared via reactive extrusion by directly mixing the peroxides. The peroxides used were dimyristyl peroxydicarbonate (PODIC C126), tert-butylperoxy isopropylcarbonate (BIC), tert-Butylperoxy 2-ethylhexyl carbonate (BEC), tert-amylperoxy 2-ethylhexylcarbonate (AEC), and dilauroyl peroxide (LP), all with a concentration of 20 mmol/kg. The influence of the temperature on the competitive prevalent reactions of degradation and branching was documented via melt mass-flow rate (MFR), rheology measurements, and gel permeation chromatography (GPC). However, via extensional rheology, strain hardening could be observed in all cases and the mechanical properties could be maintained or even improved. Particularly, PODIC C126 and LP signaled a promising possibility for LCB in this study.

Download Full-text

Improving Mechanical Properties and Biocompatibilities by Highly Oriented Long Chain Branching Poly(lactic acid) with Bionic Surface Structures

ACS Applied Materials & Interfaces ◽

10.1021/acsami.9b20264 ◽

2020 ◽

Vol 12 (12) ◽

pp. 14365-14375 ◽

Cited By ~ 2

Author(s):

Jiafeng Li ◽

Qian Chen ◽

Qin Zhang ◽

Tiantang Fan ◽

Li Gong ◽

...

Keyword(s):

Mechanical Properties ◽

Lactic Acid ◽

Surface Structures ◽

Poly Lactic Acid ◽

Chain Branching ◽

Long Chain Branching ◽

Bionic Surface ◽

Long Chain

Download Full-text

Influence of molecular structure on the foamability of polypropylene: Linear and extensional rheological fingerprint

Journal of Cellular Plastics ◽

10.1177/0021955x17700097 ◽

2017 ◽

Vol 54 (3) ◽

pp. 515-543 ◽

Cited By ~ 14

Author(s):

Ebrahim Bahreini ◽

Seyed Foad Aghamiri ◽

Manfred Wilhelm ◽

Mahdi Abbasi

Keyword(s):

Molecular Structure ◽

Small Amplitude ◽

Function Model ◽

Chain Branching ◽

Small Amplitude Oscillatory Shear ◽

Long Chain Branching ◽

Molecular Stress Function ◽

Branched Polypropylene ◽

Long Chain ◽

Long Chain Branched Polypropylene

The foaming structure and rheological properties of four different isotactic homo-polypropylenes with various molecular weights and an isotactic long chain branched polypropylene were investigated to find a suitable rheological fingerprint for PP foams. The molecular weight distribution and thermal properties were measured using GPC-MALLS and differential scanning calorimetry, respectively. Small amplitude oscillatory shear data and uniaxial extensional experiments were analyzed using the frameworks of van Gurp-Palmen plot (δ vs. | G*|) and the molecular stress function model, respectively. These analyses were used to find a correlation between the molecular structure, rheological properties and foaming structures of linear and long chain branching polypropylenes. Two linear viscoelastic characteristics, | G*| at δ = 60° and | η*| at ω = 5 rad/s were used as criteria for foamability of these polymers, where decreasing of both parameters by increasing the long chain branching content results in smaller cell size and higher cell density. The molecular stress function model was able to quantify the strain hardening properties of long chain branching blends using small amplitude oscillatory shear data and two nonlinear material parameters, 1 ≤ β ≤ 2.2 and 1 ≤ [Formula: see text] ≤ 600, where the minimum and maximum values of these parameters belong to the linear and long chain branched polypropylene, respectively. Increasing the long chain branched polypropylene content of the PP blends increased strain hardening, and therefore improved the foaming characteristics significantly by suppressing the coalescence of cells. Dilution of linear PP with only 10 wt% of long chain branched polypropylene enhanced the cell density from 5.7 × 106 to 2.7 × 107 cell/cm3 and reduced the average cell diameter from 58 to 26 µm, respectively, while their volume expansion ratio remained in the same range of 2–3. Increasing of long chain branching to 50 and 100 wt% enhanced the V.E.R. to 6.2 and 7.8, respectively.

Download Full-text