Swelling of polyethylene

Similarly, swelling of polyethylene filled with 35 and 50 wt% calcite was reduced. T able 5.13 gives equilibrium swelling of polyethylene in different solvents. 

Extrudate Swell The extrudate swell of wood-filled plastics typically increases with the flow rate (shear rate), decreases with filler loading, and practically does not depend on the melt temperature. A nonfibrous filler, such as calcium carbonate, also suppresses swell of polyethylene, and in the case of medium-density polyethylene, a swell suppression was maximal at 30% of calcium carbonate (0.4 (xm particles) [32]. A similar effect was shown using HDPE filled with rice hulls (Table 17.13). 

F. Mijangos-Santiago and J.M. Dealy. Effect of filler content and additives on the extru-date swell of polyethylene pipe resin. Polym. Eng. Sci. 1991,31(16), 1176-1181. 

An Important observation recently made concerning acid and salt effects In UV and radiation grafting to polyethylene Is that In Che swelling of polyethylene In Che presence of methanolic solutions of styrene, partitioning of styrene Into polyethylene Is significantly Improved by the Inclusion of mineral acid or lithium salt In the grafting solution. Styrene labelled with tritium was used for these sophisticated experiments which Indicate chat most swelling occurs within Che first few minutes of exposure of backbone polymer... 

Bagley E B, Storey S H and West D C (1963), Post extrusion swelling of polyethylene , Journal of Applied Polymer Science, 7,1661-1672. 

In the case of crystalline polymers better results are obtained using an amorphous density which can be extrapolated from data above the melting point, or from other sources. In the case of polyethylene the apparent amorphous density is in the range 0.84-0.86 at 25°C. This gives a calculated value of about 8.1 for the solubility parameter which is still slightly higher than observed values obtained by swelling experiments. 

The Acid Effect. The possible mechanistic role of hydrogen atoms in the current radiation grafting work becomes even more significant when acid is used as an additive to enhance the copolymerisation. At the concentrations utilised, acid should not affect essentially the physical properties of the system such as precipitation of the polystyrene grafted chains or the swelling of the polyethylene. Instead the acid effect may be attributed to the radiation chemical properties of the system. Thus Baxendale and Mellows (15) showed that the addition of acid to methanol increased G(H2) considerably. The precursors of this additional hydrogen were considered to be H atoms from thermalised electron capture reactions, typified in Equation 5. 

Three processes are used commercially to make linear polyethylene-solution, slurry, and gas phase. All are called low-pressure processes (< 50 atm) to distinguish them from the free radical or high-pressure process that makes highly branched polyethylene. In the solution mode a hydrocarbon solvent at 125-170°C dissolves the polymer as it forms. The reaction usually slows as the solution becomes viscous because it becomes difficult to stir ethylene into the liquid phase. In contrast, The slurry process uses a poor solvent and low temperature (60-110°C) to prevent dissolving or even swelling of the polymer. Each catalyst particle creates a polymer particle several thousand times larger than itself. There is no viscosity limitation in the slurry method the diluent serves to transfer heat and to keep the catalyst in contact with ethylene and other reactants. Finally, the gas-phase process is much like the slurry method in that polymer particles are formed at similar temperatures. A bed of catalyst/polymer is fluidized by circulating ethylene, which also serves as a coolant. 

In another part of this study we wished to see the effects of post-modification treatments on the properties of the modified LDPE surface. Polyethylene samples were photosulfonated for different periods of time. Afterwards they were subjected to an after-treatment by conditioning in an electrolyte solution (aqueous KC1, 10-3 M) for 48 hours and then characterized by zeta potential measurements. This conditioning process resulted in a shift of f to even less negative values (see Fig. 8). This finding may be explained by the swelling of the polymer samples (water adsorption) in water that causes a shift of the shear plane of the electrochemical double layer into the liquid phase. This effect demonstrates that storage conditions and pre-conditioning may exert a pronounced influence on the zeta potential recorded for surface-modified polymers. Phenomena of this kind have already been described in previous literature [26,27],... 

In situ polymerisation does not however guarantee homogeneous blends as two phase regions can exist within the polymer/polymer/monomer three component phase diagram. In the case of vinyl chloride polymerisation with solution chlorinated polyethylene, the vinyl chloride has limited solubility in both poly(vinyl chloride) and chlorinated polyethylene. The phase diagram has the form shown in Fig. 3 The limit of swelling of vinyl chloride in the chlorinated polyethylene is A and the highest concentration of PVC prepared by a one-shot polymerisation is B. 

Figure 1 Swelling capacity of polyethylene oxide (Polyox WSR).

Table 5.13. Equilibrium swelling of calcite-filled polyethylene. Data from...

The value of maximum swell and the location on the curve relative to ethanol concentration depend on the type of polymer (Figure 2). The fluorocarbon elastomer exhibits low swell In ethanol. In Indolene, and In the mixtures. For polyurethane and chlorosulfonated polyethylene the polymers swell slightly to moderately In Indolene and ethanol. The maximum swell of these polymers In mixtures of ethanol and Indolene Is moderate (40-56%) and occurs In a mixture containing 15% ethanol. For acrylate elastomer the swell In Indolene Is moderate (44%) but the swell In... 

Qualitatively MTBE Is estimated to have an overall solubility parameter value close to that of Indolene, but has higher polar and hydrogen bonding forces. As a result polar polymers such aa fluorocarbon, epichlorohydrin homopolymer and chlorosulfonated polyethylene tend to swell to a greater extent In MTBE rich mixtures, while nonpolar EPDM elastomer swells to a lesser extent In these mixtures. The very large swell of the fluorocarbon In MTBE Is not surprising since other ethers such as diethyl ether and dioxane are known to swell the fluorocarbon to a large extent [3]. 

Li D, Flan BX. Impregnation of polyethylene (PE) with styrene using supercritical CO2 as the swelling agent and preparation of PE/polystyrene composites. Ind Eng Chem Res 2000 39 4506 509. 

It is advisable to use a stainless steel, glass or wood spatula and a clean working area (glass, aluminum foil) or a disposable plastic cup for the mixing of adhesives (preferably polythylene or polypropylene since plastics like polystyrene, polycarbonate or polyvinyl chloride may swell due to components of the adhesive). Tip For frequent bonding processes with low adhesive consumption, even so-called pill cups (content approximately 20 ml) of polyethylene or polypropylene are suitable, which are available in drug stores. 

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