Polyamide 6 was modified with lithium chloride (LiCl) salt and N‐butyl benzenesulfonamide (N‐BBSA) plasticizer (additives). The modification was done in order to develop an environmentally friendly composite, composed of wheat straw (WS). A 15 wt% of ground WS was compounded with Polyamide 6 along with the additives. Addition of LiCl decreased the melting point of the matrix, allowing for a lower compounding temperature. However, a pseudo‐crosslinking formation upon addition of salt limited the polymer chain movement and restricted the processing temperature. LiCl addition increased the tensile and flexural modulus of the composite, but decreased the tensile and flexural strength. Decrease in the strength was found to be related to the increase in the residence time of material during extrusion causing severe WS thermal degradation. Addition of N‐BBSA eased the processing due to lubrication effect, however, when used in excess, lowered the flexural modulus and strength. Addition of WS to Polyamide 6 increased the modulus of the matrix. Matrix tensile modulus and flexural modulus were enhanced by 27%; however, a decrease in strength of the matrix was obtained. Addition of WS, LiCl, and plasticizer lowered the impact properties of Polyamide 6. It was concluded that combination of 2 wt% LiCl and of 2 wt% N‐BBSA gives the best mechanical properties. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

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Linear polypropylene (PP) was modified using UV radiation in the presence of 0.5 wt % of benzophenone photoinitiator to introduce long chain branching (LCB) to the PP backbone. Irradiation was carried out in the solid state and the temperature level was kept below 60°C. The effects of radiation duration and sample thickness on the extent of these branching modification reactions were investigated. Viscoelastic properties, molecular weight, molecular weight distribution, and gel content were determined and compared for runs having different sample thicknesses, irradiated for different times. Comparisons were also conducted with the parent PP and the PP mixed with photoinitiator. It was found that LCB decreased by increasing the thickness of the samples. Conversely, an increase in radiation duration resulted in enhanced LCB but also led to larger gel content in the samples. Based on all these measurements and observations, a mechanism was suggested to explain formation of long chain branches (LCBs) in PP in the solid state via photoinitiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41021.

A twin screw extruder was used for continuous modification of polypropylene (PP) via UV radiation. Long chain branches were incorporated in the PP backbone to modify its rheological properties. Benzophenone (BPH) as photoinitiator and trimethylolpropane triacrylate (TMPTA) as coagent were utilized during PP photomodification. Radiation was carried out after mixing in the extruder on solid stretched strands with approximately 0.3 mm thickness. The effects of photoinitiator concentration, radiation time and coagent presence were studied via a replicated two-level full factorial design of experiments. It was shown that photomodification of PP can be done continuously. Formation of long chain branches (LCBs) in the experimental runs was confirmed via rheological measurements. Gel content of the samples was also measured. It was found that long chain branches can be formed in PP with and without TMPTA at certain processing conditions. The amount of gel in the samples prepared with TMPTA was higher; however, the gel content could be controlled by manipulating BPH concentration and radiation time.

Degradation kinetics of ground wheat straw (WS), polyamide 6, and a WS‐polyamide 6 composites obtained from extrusion were investigated. 15 wt% of ground WS was melt blended with other additives naming; lithium chloride salt (LiCl) and N‐butylbenzenesulfonamide plasticizer (N‐BBSA) as matrix treatments. The additives were added to reduce the melting point of polyamide 6 and ease of composite processing (reduction in processing temperature and time). Two commonly used non‐isothermal kinetic models were used to investigate the degradation kinetics of WS and the composite. Thermal gravimetric analysis was utilized to measure the thermal stability and degradation kinetics of different composite formulation. The activation energy of WS was identified by iso‐conversional Friedman kinetic method. Through this method, WS activation energy was found to be around 141.4 kJ/mol. Composite kinetic studies were based on the Coats and Redfern procedure. It was concluded that the composite activation energy was correlated to the residual weight percentage of the composite at the maximum thermal degradation temperature. The onset of degradation of WS was dictated by the thermal stability of its lignin content and was found to be around 188°C. WS, however, did not go through a major degradation up to 245°C at which drastic decomposition starts. This temperature range overlaps with processing temperature of Polyamide 6 and required matrix/WS treatments. Addition of salt and plasticizer individually or with each other at any level decreased the onset of degradation temperature. Addition of plasticizer at 4 wt% level, however, shifted the degradation peak to higher temperature representing a more thermally stable composite. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Summary: UV radiation with a photoinitiator has been utilized to modify polypropylene (PP). Factors affecting solid state photomodification were studied and the optimal processing conditions for formation of three different structures (degraded, long chain branched and crosslinked) in PP were determined. A long radiation time (more than 5 minutes) is required to form long chain branched PP (LCBPP) and this exposure time is even higher for production of crosslinked PP (XPP). Trimethylolpropane triacrylate (TMPTA) was utilized to decrease UV radiation duration. Optimal concentrations of TMPTA and photoinitiator for formation of long chain branched and crosslinked PP were determined. Finally, a setup was suggested for continuous photomodification of PP using a twin screw extruder. In this design, PP strands are irradiated directly after the die. Optimal photoinitiator (benzophenone) concentration, coagent (TMPTA) concentration and radiation time required to form controlled rheology (CRPP) or long chain branched PP or crosslinked PP were identified.

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