• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.88-92
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• 2012

Decrosslinking of crosslinked polypropylene(XLPP) in supercritical methanol was investigated compared with that of crosslinked polyethylene(XLPE). Effect of reaction temperature and initial gel contents was studied using a batch reactor. Gel contents of samples before and after reaction were measured for quantitative analysis. As reaction temperature and initial gel contents increased, the decrosslinking rate increased. The rate of decrosslinking reaction is dependent linearly on the gel contents. Experimental results indicated that the decrosslinking of XLPP was faster than that of XLPE, and it was confirmed quantitatively by the calculation of kinetic constants. In conclusion, it is considered that XLPP has better recyclability than XLPE.

• Journal of Pharmaceutical Investigation
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• v.24 no.4
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• pp.251-256
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• 1994

Polypropylene glycol (M.W. 4000) was crosslinked and chain-extended by using triisocyanate and diisocyanate to synthesize rubbery and water swellable hydrogels. Model drugs, i.e., sodium salicylate and indomethacin were incorporated in the polymer matrices by swelling loading. The drug release rates of drugs could be regulated by varying the degrees of crosslinking and chain-extension. Whereas, no correlation was observed between the drug release profiles and the swelling behaviours of the matrices. The release of drugs from the matrices was considered to be governed by the mobility and mesh size of the polymer chains in the matrices.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.69-73
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• 2010

The melt grafting of unsaturated silanes onto polypropylene (PP) in a twin-screw extruder and crosslinking in hot water were studied to enhance impact strength of polypropylene. The influence of grafting formulations on the melt flow rates of grafted PP and the gel percentages of crosslinked PP was investigated. 3-methacryloylpropyltrimethoxysilane (VMMS) unsaturated silane monomer was used. Benzoyl peroxide, (BPO) and Dicumyl peroxide (DCP) were used as an initiator. When benzoyl peroxide (BPO) was used as an initiator, higher gel percentage and impact strength than those of DCP has been observed. The maximum impact strength was obtained with 0.7 phr of BPO and 2phr of VMMS. The value is 8.7 kgf-cm/cm and it is on a parity with the value of with 20 phr of EOR mixed to PP.

• Journal of Pharmaceutical Investigation
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• v.21 no.2
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• pp.91-95
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• 1991

Polyethylene glycol, polypropylene glycol and block copolymer of ethylene glycol and propylene glycol were crosslinked by triisocyanate to form water swellable, rubbery polymer. The equilibrium swelling of the hydrogels ranged from 3% to 60% according to the hydrophobic-hydrophilic properties of the prepolymers. Model drugs, sodium salicylate and prednisolone were incorporated in the polymer matrices by swelling loading. Physical properties of the drugs affected the drug release mechanisms due to the change in the swelling behaviors of the polymeric devices. Zero order release was observed in the case of relatively hydrophobic polymer matrices.

• Polymer(Korea)
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• v.26 no.1
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• pp.61-70
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• 2002

The effects of molecular weights and rheological properties of polypropylene (PP), on its foam structures in batch process were investigated. The effects of crosslinking process were also considered in this study. The rheological properties of polypropylene, such as storage modulus(G'), loss modulus(G"), zero shear viscosity($\eta_O$), and relaxation time($\lambda$), increased with the increase of molecular weights, and these increases in rheological properties directly affected the stability improvements of the PP foam. The increase of crosslinked PP's gel content stopped at the irradiation dose of 3.2 Mrad. The development of foam structures was more enhanced as the irradiation dose increased up to 3.2 Mrad. When the irradiation dose exceeded 3.2 Mrad, however, it negatively affected the structural development of the foam by diminishing gel contents of the foaming material, which resulted in instability of the foam structure.ture.

• Polymer(Korea)
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• v.26 no.4
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• pp.508-515
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• 2002

The effects of the crosslinking caused by irradiation dose, molecular weights of the foaming materials, and various foaming processes on the foam structure of the polypropylene (PP) were investigated. The maximum gel content of the PP was 48% when the sheet was irradiated with 3.2 Mrad. This high gel content improved the cell structures by providing high thermal stability. The increase of both the gel content and structural development were stopped at the irradiation dose exceeding 3.2 Mrad. The increase of the molecular weights served to help produce a foam with particularly fine and even cell structures, along with improved thermal stability as well.

• Journal of Adhesion and Interface
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• v.20 no.2
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• pp.66-70
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• 2019

The surface of hydrophobic polypropylene (PP) fibers (spun-bonded fabric) was treated by an atmospheric plasma treatment method. These pre-treated hydrophilic PP fabrics were dip-coated in the aqueous poly(N-vinyl pyrrolidone) (PVP) solution. PVP layers on the surface of PP fiber were crosslinked by an irradiation of electron beam. The thickness of PVP hydrogels coated on the surface was easily controlled by changing the concentration of PVP in coating solution. The stepwise surface treatment, PVP coating, and hydrogel formation via electron beam irradiation were analyzed by the measurement of contact angle, scanning electron microscopy, and optical microscopy.

• Elastomers and Composites
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• v.52 no.1
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• pp.35-47
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• 2017

A comprehensive survey of the available literature showed that in the last few decades, there has been a growing interest in the use of thermoplastic vulcanizates (TPVs). TPVs are the second largest group of soft thermoplastic elastomers (TPEs) after styrene-based block copolymers, and offer a wide range of potential and proven applications, including in mechanical rubber goods, under-the-hood applications in the automotive field, industrial hose applications, electrical applications, consumer goods, and soft touch applications. Over the last two decades, TPVs have shown a strong and steady market growth (~12% per year). Commercialized TPVs are commonly based on blends of ethylene propylene diene monomer (EPDM) rubber and polypropylene (PP), and to a lesser extent on combinations of butyl or nitrile rubber with PP. EPDM/PP TPVs are characterized by finely dispersed crosslinked EPDM rubber particles (particles size varying between 0.5 and $2.0{\mu}m$) distributed in a continuous thermoplastic PP matrix. If the rubber particles of such a blend are small enough and if they are vulcanized well enough, then the properties of the blend are generally improved. This review article introduces various topics and aspects relevant to EPDM/PP TPVs. The development of TPVs, the use of various types of crosslinking systems and co-agents as crosslinking agents for PP/EPDM blends, the morphology and rheology of TPVs, and their typical end-use applications are also reviewed.

• Advances in materials Research
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• v.4 no.3
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• pp.145-164
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• 2015

Biodegredable and injectable nanocomposites based on polypropylene fumarate (PPF) as unsaturated polyester were prepared. The investigated polyester was crosslinked with three different monomers namely N-vinyl pyrrolidone (NVP), methyl methacrylate (MMA) and a mixture of NVP and MMA (1:1 weight ratio) and was filled with 45 wt% of hydroxyapatite (HA) incorporated with different concentrations of chemically treated natural bone powder (NBP) (5, 10 and 15 wt%) in order to be used in treatment of orthopedics bone diseases and fractures. The nanocomposites immersed in the simulated body fluid (SBF) for 30 days, after the period of immersion in-vitro bioactivity of the nanocomposites was studied through Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy dispersive X-ray (EDX) in addition to dielectric measurements. The degradation time of immersed samples and the change in the pH of the SBF were studied during the period of immersion.

• Elastomers and Composites
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• v.32 no.3
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• pp.157-165
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• 1997

The morphology of the thermoplastic vulcanizates prepared from ethylene-propylene-diene terpolymer, polypropylene and high density polyethylene(HDPE) or ethylene based ionomer were studied. Blends were prepared in a laboratory internal mixer where EPDM was cured in the presence of PP and HDPE or ionomer under shear with dicumyl peroxide(DCP). The effects of DCP concentration and rubber/plastics composition were studied. In the morphological analysis by scanning electron microscopy (SEM), a small amount of EPDM acted as a compatibilizer to HDPE and PP. It was also revealed that the dynamic vulcanization process could reduce the domain size of the crosslinked EPDM phase. When ionomer was added to EPDM/PP blend, the thermoplastic vulcanizate showed typical ductile fracture topology and the trend was more clearly observed when DCP contents and ionomer contents are higher.