Jeanette González

Polypropylene/wood flour composites: treatments and properties

In this research, the variations produced on the mechanical, morphological and thermal properties and on the melt index (MI) of a composite of polypropylene and wood flour (WF) by the modification of the filler were studied. The filler was treated with sodium hydroxide at different immersion times and with vinil-tris-(2-metoxietoxi)-silane. Polypropylenes functionalized with maleic anhydride (maleated polypropylene, MAPP) were also used as compatibilizers. All the treatments showed the same tendency to slightly increase tensile modulus and tensile strength of the composites, but they did not affect their MFI. Morphological studies showed that the MAPP and silane improve the polymer–WF adhesion and the dispersion of the particles, while the alkaline treatment only improves the dispersion. The silane-modified samples and the use of MAPP produced samples with lower water absorption than those of untreated WF composites. The addition of the filler and the treatments carried out on it caused an increase in the crystallization temperature.

Thermal stability of blends of polyolefins and sisal fiber

Abstract This paper deals with the effect of acetylated and non-acetylated fiber on thermal degradation of blends of PP and polyolefins, specifically: PP/HDPE, PP/HDPE/functionalized EPR and PP/HDPE/non-functionalized EPR. To determine activation energy, the thermograms were analyzed through the Horowitz–Metzger (H–M), Coats–Redfern (C–R), and Reich–Stivala (R–S) integral methods. The studies have shown that the starting temperature of the decomposition of the fiber, whether treated or not, is maintained almost at the same level. Acetylated fiber stability was also found to increase, because activation energy ranged between 119 and 171 kJ/mol, depending on the method used; for non-acetylated fiber it was between 98 and 148 kJ/mol. This could be attributed to the fact that the fiber was fibrilized when it was treated with alkali, which resulted in a rough surface. This phenomenon can be the result of the substitution of OH groups by more voluminous ones, which brings about restrictions in the segmental mobility, thus increasing rigidity in the main cellulose chain. Activation energy of PP and PP/HDPE and PP/HDPE/functionalized and non-functionalized EPR blends ranges between 250 and 180 kJ/mol. When they are mixed with treated and non-treated fiber, a sudden decrease in activation energy is observed and this effect is slightly clearer with the untreated filler. This could be explained because mixing acetylated fiber with polymers results in higher polymer-filler interaction, which favors thermal stability of the compounds. These results let us infer that a satisfactory profit/cost relation justifies treating fiber for adding it to PP and to PP/HDPE and PP/HDPE/EPR blends.

Effects of coupling agents on mechanical and morphological behavior of the PP/HDPE blend with two different CaCO3

Abstract The main purpose of incorporating fillers, such as calcium carbonate, into blends of polyolefins is to decrease costs and change tensile and impact properties. Structural differences between both components give rise to the formation of large filler agglomerates in the polymer matrix, which influence the mechanical response of the material. Therefore, the coupling agents of the Lica 12 type at various concentrations was used to facilitate the link between filler and matrix (the latter consisting of PP/HDPE 80/20 wt). Filler was added to the PP/HDPE blend at a 30 wt.% concentration. Two types of calcium carbonate (CaCO3) were used. These have different average sizes (3.0 and 1.8 μm) which were determined by means of laser diffraction techniques. In addition other coupling agents of the titanate type, such as Lica 09, Lica 01, zirconates ZN 12, and a 1:1 mixture of Lica 12 and Lica 01, were used. This study clearly demonstrated that the addition of the coupling agent to CaCO3 modifies the mechanical properties of the PP/HDPE/CaCO3 composites. Values of the mechanical properties indicate that due to its characteristics, each coupling agent gives rise to increases in a particular mechanical property. In the case of Lica 01 an increase was verified in Young’s modulus at 0.7 wt.% and in elongation at break at both concentrations (0.3 and 0.7 wt.%), whereas ZN 12 brought about an increase in elongation at break. The 1:1 mixture of Lica 12 and Lica 01 caused impact resistance of the blend of PP/HDPE with CaCO3 to increase considerably.

Analysis of the mechanical, thermal and morphological behaviour of polypropylene compounds with sisal fibre and wood flour, irradiated with gamma rays

Abstract We report a study of the mechanical, thermal and morphological behaviour of blends of polypropylene filled with wood flour and sisal fibre (at 60/40 and 80/20 compositions, respectively), subjected to different doses of gamma irradiation (10, 25, 30, 50, 60 and 70 kGy), at room temperature and in the presence of oxygen. In addition, studies were carried out by infrared spectroscopy and electronic paramagnetic resonance to analyse the formation of radicals or functional groups influencing the behaviour of the irradiated compounds. Low irradiation doses improve the mechanical behaviour of the compounds under study (PP/wood flour, PP/sisal fibre). Thermal stability is acceptable and radical concentration in these materials is low. It was also demonstrated that it is possible to use low irradiation doses to modify the characteristics of PP and filler, which means a number of advantages: no chemical reagents are required and there are no residual polluting by-products or tedious post-treatment. Gamma-irradiation, therefore, is a promising technology to modify these composites in industry.

Effects of filler treatments on the mechanical and morphological behavior of PP+wood flour and PP+sisal fiber

Abstract Composites were prepared from waste wood flour, sisal fiber and polypropylene (PP). The surface of the filler was modified to enhance the chemical affinity between hydrophilic cellulosic and hydrophobic polymer. The treatments studied were: a) The addition of a coupling agent; b) chemical treatment with NaOH; and c) the addition of functionalized polypropylene (Polybond 3150 and 3200). After treatment, mixtures of PP with 40% and 20% of the filler, wood flour and sisal fiber respectively, were extruded and injection molded. In the case of wood flour, a mixture of two particle sizes (mesh 20 and 40, 50% each) was used, and in the case of sisal, 10 mm long fibers were selected. Results showed that, regardless of the treatment to which the filler was previously submitted, Young’s modulus was always higher for mixtures prepared with wood flour, with values varying between 2839 and 3150 MPa. Whereas for mixtures with sisal fiber, the modulus’ values varied between 1704 and 2220 MPa. Values of breaking strength, elongation at break and impact strength for PP mixtures with treated sisal fiber were always higher than those for mixtures of PP with wood flour. Based on these results, we can conclude that sisal fiber is an organic filler which, due to its mechanical and morphological characteristics, has a reinforcing effect higher than that of wood flour.

Grafting of polyethylenes by reactive extrusion. I. Influence on the molecular structure

Grafting of polyethylenes is an important method used in the modification of polyolefins with functional groups. Lately, the use of extruders as polymerization reactors has increased considerably. However, knowledge of the details of the reaction in the extruder is still limited. In this investigation, the grafting of various commercial polyethylenes, high-density polyethylenes (HDPEs), and linear low-density polyethylenes (LLDPEs) with diethyl maleate (DEM) was carried out in two corotating twin-screw extruders with different screw configurations and extrusion conditions. Two initiators at different concentrations were used. It was found that when the initiator level was raised in the LLDPEs the grafting degree increased and the molecular weight distribution of the grafted LLDPE2 did not show appreciable differences when they were compared to the virgin resin. On the other hand, the terminal vinyl group concentrations decreased at the expense of increasing the trans unsaturation concentrations. This last result is consistent with the formation of long-chain branching. Additionally, the weight-average molecular weight of grafted high-density polyethylene (HDPE1-g-DEM) decreased. The grafting efficiencies were consistent with the attained residence times and also with the kinetics of the decomposition of the peroxides.

Mechanical, thermal and morphological behaviour of the polystyrene/polypropylene (80/20) blend, irradiated with γ-rays at low doses (0–70 kGy)

Abstract The effect of low doses (0–70 kGy) of gamma irradiation on the mechanical, morphological and thermal behaviour, at room temperature and in the presence of oxygen, of a polystyrene/polypropylene (PS/PP) blend (80/20) with and without compatibilizer (block SBS) at 7.5 wt.% has been studied, to solve different problems related to the radiation stability of polymeric articles and purposeful radiation-induced modifications of polymeric materials. The effect of gamma irradiation on the tensile behaviour of the PS/PP blend (80/20) with and without SBS indicates that the blends present a high irradiation resistance at low doses (⩽70 kGy); this implies that adding PP to PS to modify its mechanical behaviour is a proper procedure, since PS is one of the most stable polymers regarding radiation, and very large doses are required to produce any noticeable change. Therefore, with an irradiation dose ranging between 0 and 70 kGy, PP is protected against a strong oxidative degradation (chain scission), which coincides with the values of the relative concentration of radicals obtained through EPR. In addition, according to the thermal studies, T g shows no variations which could point to changes in the PS structure in the blends; however, variations in T f of PP of the blends were detected, which lead us to conclude that PP shows chain scission degradation. It can be inferred that this decrease in fusion temperature occurs in the blends at irradiation doses (⩾50kGy) higher than that of non-compatibilized PP (⩾10kGy).

MECHANICAL AND MORPHOLOGICAL BEHAVIOR OF POLYOLEFIN BLENDS IN THE PRESENCE OF CACO3

Abstract The aim of the present work is to study the properties of blends of Polypropylene (PP) with virgin and recycled high density polyethylene (r-HDPE) (80/20), functionalized and non-functionalized EPR (5 wt%), and calcium carbonate (30%) as it is untreated or treated with a 1% by weight of coupling titanate agent. The mechanical behavior of PP/HDPE/EPR blends showed that functionalization was not effective. When blends of PP/HDPE/EPR with treated or untreated filler were compared to the equivalent ones, but with recycled HDPE and untreated filler, a slight increase was observed in elongation at break and a decrease in Young’s modulus and impact strength. This behavior may suggest that recycled HDPE and EPR together act as a plastifier in these blends. It was also found that the use of treated calcium carbonate did not contribute to obtain better mechanical properties. From these results it can be concluded that it is possible to recycle HDPE in blends with PP and non-functionalized EPR (nf-EPR), using untreated calcium carbonate as a filler, and that this offers economic advantages and produces a material with mechanical properties comparable to those of the compounds of PP with filler.

Analysis of thermogravimetric data of blends of polyolefins with calcium carbonate treated with Lica 12

The objective of this work was to determine the kinetic parameters and the possible reaction mechanism in the polymer thermal decomposition using the software TGAnalyzer and analyze the effect of a titanate coupling agent (Lica 12) on thermal degradation of polyolefin blends, specifically polypropylene/high-density polyethylene (PP/HDPE), polypropylene/high-density polyethylene/ethylene-propylene copolymer (PP/HDPE/EPR) with 30 wt.% of calcium carbonate (CaCO3) untreated and treated with 1% Lica 12. Recycled high-density polyethylene (r-HDPE) was also included in the aforementioned blends. Dynamic thermograms were obtained for each blend so that different methods could be applied for determining activation energy, reaction order and possible mechanism of decomposition. According to the results obtained for the activation energy (Ea), the addition of CaCO3 to the PP/HDPE/EPR blends does not significantly influence their thermal stability. The results showed that the optimum filler concentration was 30 wt.%. Blends of PP/HDPE with treated CaCO3 exhibit Ea values higher than those of the blends containing EPR, which means that Lica 12 has an accelerating effect on the decomposition of these blends with EPR. In addition, the recycled material was found to decrease activation energy of the blends. Morphological observations help us determine that Lica 12 influences thermal stability, by increasing activation energy, with a better dispersion of the blend components. For all the samples studied in this work, the reaction mechanisms are diffusion and Limiting surface reaction between both phases, in three dimensions and three ways (D3 and R3).

Dynamic thermal decomposition of blends of polyamide 6 with functionalized and non-functionalized PP

Abstract The processes of thermal degradation taking place in polyamide 6 (PA6) blends with functionalized (PP1-g-DEM) and non-functionalized polypropylene (PP2) have been studied by thermogravimetric analysis. Coats–Redfern, Van Krevelen and Horowitz–Metzger integral methods were used to determine kinetic parameters. It was observed that the starting temperature of the decomposition of the blends decreases from 380 to 340°C when increasing the concentration of functionalized polypropylene. When non-functionalized polypropylene is used, the decrease is from 360 to 300°C. On the other hand, although the activation energy of the functionalized polypropylene is smaller than that of the non-functionalized, it was demonstrated that the thermal stability is bigger for the mixtures of PA6 with PP1-g-DEM, the latter being at 30 wt% composition of PP. Also, the use of functionalized polypropylene in the blends with polyamide evidences a better dispersion and a smaller particle size; this behavior positively influences the thermal stability of these blends.