Color and UV Stabilization in Pigmented Injection-Molded Polypropylene

Abstract

A previous application of mind by Kanu, Spotts, and Chesebrough showed that more [i]or[/i] less organic and inorganic pigments noticeably influence the tensile and impact properties of injection-molded polypropylene1 As an extension of the previous close attention this work examines the influence of the same organic and inorganic pigments upon the color and UV stabilization of injection-molded polypropylene specifically the action of these pigments as nucleating agents in the crystallization proces of the semi-crystalline polypropylene However, since organic and inorganic pigments have different chemical compositions and particle sizes, their action as nucleating agents will differ and consequently determine the stage of influence they exert upon the properties of injection-molded polypropylene

Introduction

Plastics have made significant contributions to our standard of living. In many applications, similar as in medical uses for hip bone and heart valve replacement, plastics are many times the preferred material because their inherent properties make them more suitable than traditional materials like ceramics, forest-land and metals. For example, Kevlar fibers are used in bulletproof dresss and some combat protective helmets because of their high strength-to-weight ratio, and the polycarbonate material known as Lexan is used in ophthalmic lense because it is lightweight, tough, and transparent.

While intrinsic properties make plastics attractive for many applications, the advantages of this material are single realized when the plastic resins are transformed into useful existences by primary processing techniques like as injection molding, extrusion, thump molding, rotational molding, compression and transfer molding, and thermoforming. However, if not done suitably the fabrication process that not single results in significant benefits can also diminish plastics' attractive properties. For example, an abnormally high processing temperature exerciseed in a fabrication process like as injection molding can degrade the plastic material, resulting in a finished fruits with lower mechanical properties and perhaps unacceptable visual issues such as blemishes and consume marks. Another potential disadvantage in the transformation proces is the use of additives to achieve specific features in the finished returnss For example, flame retardants are used to hinder plastic television casings from bursting into flames in the neighborhood of electrical sparks, and processing aids or lubricants similar as waxes are used to improve production of PVC pipes and vinyl sidings. In a certain quantity of cases, additives do achieve the awaited results but also cause unpredictable characteristic changes in the finished product; hence, additives may improve a product's mechanical properties while simultaneously reducing its processiblity. Given this background, the authors examined the issues of some organic and inorganic pigments upon the color and ultraviolet (UV) stabilization of injection-molded polypropylene (PP) tensile specimens.

Motivation

There are several studies that have sought to clarify the results of additives on the physical, mechanical, optical, and rheological properties of polymeric materials. Jaffe et al. investigated Theologically effective organic pigments, and Yu et al. studied the issues of carbon black dispersion upon polymer performance.2,3 Other authors like Spano and Steen examined the optical properties of pigmented polypropylene while Krisher and Marshall studied the events of pigments on the mechanical properties of polypropylene45 In another investigation Charvat et al. examined the shift in color in pigmented plastics after the injection molding of plastic parts.6 agreeing with these studies is a discussion within the plastics industry concerning the use of the pair organic and inorganic pigments in the manufacture of plastics fruitss primarily because of health and environmental concerns; inorganic pigments are known to contain traces of potentially harmful impurities of that kind as dioxins as well as heavy metals of that kind as cadmium, lead, chromium, and mercury78 To address these belong tos this study sought to examine and compare the influence of organic and inorganic pigments upon the color and UV stabilization of injection-molded polypropylene A secondary goal was to use the application of mind as a pedagogical tool to reinforce important theoretical conceptions involving pigmentation of plastics, injection molding, extrusion, reflectance spectrophotometry, and amorphous, semicrystalline, and nucleated crystallization properties.

Definitions

The following section defines a certain number of key concepts and technical terminuss used in this paper.

AMORPHOUS PLASTICS

In the amorphous state, plastics indivisible particles exhibit no definite form of order. upon a molecular scale, this state has been aptly described as resembling a goblet of cooked spaghetti.9 The nature of amorphous plastics is predominately amorphous while in the solid state, and mainly because of their irregular molecular form these materials show no bias to crystallize. Examples of amorphous plastics are poly (methyl methacrylate), commercially known as acrylics (Atohaas' Plexiglas, Id's Lucite and Cyro Industries' Acrylite); polycarbonate (GE Plastics' Lexan); and atatic polystyrene commercially known as generalpurpose polystyrene or crystal polystyrene