Process for fabricating polypropylene sheet

Abstract

A process for production of a monolithic article from a web of fibres of oriented polypropylene polymer, comprising the steps of subjecting the web to elevated temperature and pressure sufficient to melt a proportion of the polymer and compact it, and then cooling the compacted web, wherein an accelerated rate of cooling is employed down to 100° C. The process is of particular benefit when the weight average molecular weight (M w ) of the fibres is 250,000 or below. The resultant articles have good stiffness and strength, yet with reasonable ductility. Similar articles cooled slowly are brittle.

1 . A process for production of a monolithic article from a web of fibres of oriented polypropylene homopolymer or copolymer, comprising the steps of subjecting the web to elevated temperature and pressure sufficient to melt a proportion of the polymer and compact it, and then cooling the compacted web, wherein an accelerated rate of cooling is employed down to a lower temperature and in which said lower temperature is a predetermined amount below the recrystallisation temperature of the fibres.  
     
     
         2 . A process for production of a monolithic article from a web of fibres of oriented polypropylene homopolymer or copolymer, comprising the steps of subjecting the web to elevated temperature and pressure sufficient to melt a proportion of the polymer and compact it, and then cooling the compacted web, wherein an accelerated rate of cooling is employed down to 100° C.  
     
     
         3 . A process as claimed in  claim 1  wherein the compacted web is cooled at a mean rate of at least 10° C. per minute, down to 100° C.  
     
     
         4 . A process as claimed in  claim 2  wherein the compacted web is cooled at a mean rate of at least 30° C. per minute, down to 100° C.  
     
     
         5 . A process as claimed in  claim 1  wherein the compaction pressure does not exceed 10 MPa.  
     
     
         6 . A process as claimed in  claim 1 , wherein the fibres are melt formed fibres.  
     
     
         7 . A process as claimed in  claim 1  wherein the weight average molecular weight (Me) of the fibres is in the range 100,000 to 800,000.  
     
     
         8 . A proccss as claimed in  claim 7  wherein the weight average molecular weight (M w ) of the fibres is in the range 100,000 to 250,000.  
     
     
         9 . A process as claimed in  claim 8  wherein the weight average molecular weight (M w ) of the fibres is in the range 150,000 to 220,000.  
     
     
         10 . A monolithic article manufactured by a process as claimed in  claim 1 , having a matrix phase of polymer which was produced by selective melting of the oriented phase during the process and an oriented fibre phase a fraction of which was melted during the process.  
     
     
         11 . A monolithic article as claimed in  claim 10  wherein the Young's modulus of the matrix phase is at least 0.9 GPa.  
     
     
         12 . A monolithic article as claimed in  claim 10  wherein the failure strength of the matrix phase is at least 20 MPa.  
     
     
         13 . A monolithic article as claimed in  claim 10 , wherein the failure strain of the matrix phase is at least 5%.  
     
     
         14 . A monolithic article as claimed in  claim 10  wherein the Young's modulus in the longitudinal direction of the oriented fibre phase is at least 4 GPa.  
     
     
         15 . A monolithic article as claimed in  claim 10  wherein the failure strength in the longitudinal direction of the oriented fibre phase is at least 250 MPa.  
     
     
         16 . A monolithic article as claimed in  claim 10  wherein the failure strain in the longitudinal direction of the oriented fibre phase is at least 5%.  
     
     
         17 . A process of fabricating a monolithic article comprising polypropylene polymer or copolymer, or a monolithic article thus formed, substantially as hereinbefore described with particular reference to the accompanying examples.