Weld-line strength

PP/HDPE= 1 1 processability, weld-line strength. Moorwessel a/., 1974... 

Blends of PC/PET/TPU with EVAc-GMA and optionally MBS or ABS, have good flexural modulus, strength, weld line strength, solvent resistance, and impact behavior [Laughner, 1994]. PC blends with a polycaprolactone-polyurethane resin, TPU Pellethane , and either MBS or MBA showed similar behavior [Henton et al., 1993]. 

An alloy made from hquid crystal polyester and PPS can be used in electrical and electronics connectors, thin walled parts, and multi-gated parts. The two materials complement each other, as the LCP offers good reinforcing strength and allows for good flow into thin sections without flash. The PPS reduces the alloy s cost, cuts warpage, and increases weld line strength. Also, the material can be processed in LCP molds. 

Figure 6.9 Weld line strength of PS and PMMA vs. melt temperature, with predictions from a diffusion model (Gao, S. et o/.. Polymer, 45, 2911, 2004) Elsevier.

Chookaew et al described the effects of filler types and contents on the weld line strength of NBR, suggesting that an increased amount of CaCOs has little effect on the weld line strength, whereas in the case of Si02 the weld line strength of NBR is far lower than the values obtained for the samples absent of... 

An important application for polybntylene is plumbing pipe for both coimnercial and residential use. The exceUent creep resistance of polybntylene aUows for the manufacture of thiimer wall pipes compared to pipes made from polyethylene or polypropylene. Polybutylene pipe can also be used for the transport of abrasive fluids. Other applications for polybutylene include hot melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybntylene is also used in pack aging applications. 

Figure 8.24 Weld line strengths of unfilled and filled Thermx LCP at two different conditions. HIGH means high temperature, high pressure, and high injection speed LOW means low teinter-ature, low pressure, and low injection speed [100].

The entanglement of the polymer chains at the weld line is related to their diffusion rate, which is a function of temperature and melt viscosity of the polymer [95]. The holding pressure in the cavity and the injection speed can also affect the weld line strength [96]. Many predictive models for the weld line strength of thermoplastic amorphous polymers in relation to the viscoelastic properties and processing conditions such as the melt temperature, the mold temperature, and the holding time, have been proposed [97-99]. 

In these blends, ABS s role is to improve flowabihty and reduce cost, while that of PSF is to improve the shape retention at high temperatures. ABS/PSF blends are compatibilized either by phenoxy, EVAc-GMA, or SMA copolymers. They have good processability, high notched Izod impact strength, plateability, hydrolytic stability, and economy. However, they may show poor surface and weld-line strength. Arylon and Mindel A are examples of the commercial ABS/PSF alloys, while Ucardel is an example of PSF blends with SAN. Evolution of ABS/PSF blends technology is summarized in Table 1.19. 

HDPE was blended with 50 wt% PP, having matched melt flow index, to give good flowability, weld-line strength, surface quality, and low-temperature impact strength... 

These unique combinations of transparency, hydrolytic, and heat resistance of polysulfones would be lost if other polymers are blended. Hence, there has been very little commercial incentive for blends of polysulfone. Nevertheless, in the early days of polysulfone commercialization, some blends with ABS and PET were developed primarily to lower the cost but also to improve selected properties such as plateability or chemical resistance. A PSU/ABS blend (Mindel A) was commercially offered for some time but is now no longer available. Additives such as phenoxy resins, styrene-maleic anhydride copolymers have been claimed to improve the compatibility and weld-line strength of the PSU/ABS blends (Robeson 1985). The blend was evaluated for selected appliance, plumbing, and sterilizable equipment plated parts. This blend lacked the heat resistance needed for the vapor phase solderability in electronic applications. 

A new approach to increase weld line strength of incompatible polymer blend composites selective filler addition. Polymer, 45, 1243. 

The multiple functions of mica have been outlined in Chapter 1 of this book, along with an example of its role in the search of multifunctional fillers for polypropylene compounds for automotive applications. Mica-reinforced thermoplastics such as polypropylene, polyethylene, nylon, and polyesters are now established in a variety of automotive applications and consumer products where mica supplements or replaces glass fibers and other mineral fillers. The wider use of mica in many applications has been limited by low impact strength and low weld-line strength in certain plastics. These issues are the focus of continuing R D efforts by materials suppliers and compounders/molders. 

Polycarbonate (PC) 15-40 Automotive exterior body applications (i.e.. fascia and side cladding parts) Improved weld-line strength Improved flex modulus Low CLTE Improved siuface appearance... 

Internal lubricants typically reduce bulk viscosity by being partially compatible with the polymer, with the lubricant s soluble component helping to open the polymer chain, and the less soluble portion of the lubricant molecule providing intermolecular lubrication (e.g., fatty alcohols, esters, ethylene-vinyl acetate waxes). They promote flow with a reduction in die swell. In injection moulding, the provide improved weld line strength, clarity, die filling and rate of production. In extrusion it reduces head and back pressure while affecting paintability. However, an increase in internal lubricants lowers heat distortion. 

External lubricants typically provide lubrication between the polymer and the metal surface of the processing equipment, and include PE homo polymers, paraffins, esters, metallic soaps, amides, fatty acids and oxidised PE. In injection moulding they help with mould release and reduce the process temperature. However, an excess of external lubricants can promote plate out, cause delamination, lower weld line strength and cause surging with slow fusion. 

Other applications include hot-melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybutylene is also used in packaging applications. 

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